Monday, March 17, 2014

Climbing the Geology and Tectonics of Katahdin: An Exhumed, Glacially Sculpted, Devonian-Age Pluton

“The tops of mountains are among the unfinished parts of the globe,
whither it is a slight insult to the gods to climb and pry into their secrets,
and try their effect on our humanity.
Only daring and insolent men, perchance, go there.
Simple races, as savages, do not climb mountains,
their tops are sacred and mysterious tracts never visited by them.
Pamola is always angry with those who climb to the summit of Ktaadn.”
The Maine Woods by Henry David Thoreau, 1864
who employs a phonetic spelling of Katahdin.

We're facing east from Baxter Peak at 5,269 feet, the ultimate summit of Katahdin's five peaks and the highest point in the State of Maine. The afternoon sun is casting long October shadows into the semi-circular abyss of glacial ice-gouged South Basin. A vertiginous 2,000 foot headwall of erosion-resistant Katahdin granite rises to the top of Pamola Peak across the cirque. To the right of Pamola and running to the summit on which we're standing is a daring traverse called the Knife Edge. It's a two-foot wide boulder-scramble on the apex of a glacial arête that is both famous and revered throughout the northeast. 
Textbook glacial tarns, hummocky moraines and serpentine eskers lie on a heavily forested, boulder-strewn outwash plain across the valley floor. Welcome to Katahdin!

Classic Glacial Features From Atop Baxter Peak
This two-photo panorama was taken from the summit of Baxter Peak, one of five satellite peaks that lie on Katahdin's horseshoe-shaped rim. In the middle distance bask North and South Turner Mountains, and beyond the horizon lies the Bay of Fundy of Nova Scotia. Please click for a larger view.

Pronounced "kuh-TAH-din", it's a Penobscot word of Maine Native Americans that means "the greatest mountain", so the need for "Mount" is redundant. Katahdin and its features harbor geological secrets of their past that have plagued geologists for over a century.

What is the tectonic relationship of Katahdin to the Appalachian Mountain chain along North America’s eastern margin? By what tectonic design did Katahdin's granitic core emplace? How did did Katahdin come to be positioned within a middle Paleozoic “sea” of metasedimentary rock? Katahdin's calderic-appearing profile resembles that of Mount St. Helens. Do they share a common volcanic geo-genesis? Why does Katahdin’s granitic core become redder and more resistant to erosion with elevation?

The granites of Katahdin and the rhyolites of nearby Traveler Mountain exhibit a remarkable chemical homogeneity and time of emplacement. In fact, a contact exists where one intrudes the other. Is there a geological association between Katahdin and Traveler Mountain? By what process did Katahdin’s subterranean magma chamber become "the greatest mountain" towering above the others in the region? 

Great Basin by American landscape oil painter Frederic Edwin Church (1826-1900), 1852.

Why is Katahdin’s western flank an upward slope to a high plateau, while its east side is a steep, glacier-sculpted collection of cirques? Did the Laurentide ice sheet of the Pleistocene carve all of Katahdin’s features or did alpine glaciers contribute to the job?

Penobscot mythology exalts Pamola - part moose and part eagle - as the prisoner-taking spirit of thunder and supreme protector of “K’taadn.” Our fervent hope on this near-freezing Columbus Day weekend, the last of the hiking season in Baxter State Park of Maine, was that the mysterious winged deity would hold mountain storms, lightning strikes and high winds at bay, and repress his anger long enough for us to ascend his granite fortress, observe its geology - and return safely.  

Baxter Peak and the Knife Edge from Atop Pamola Peak
This view faces west from Pamola Peak toward Baxter Peak, the opposite perspective from the photo above. The hikers at the left are on a section of the mile-long Knife Edge Trail. Notice the rubble that litters the summit. This is a Wikipedia photo.

About 90 miles upstream from Penobscot Bay in mid-coastal Maine, the Penobscot River divides into a West and East Branch. Between the two branches is the edifice of Katahdin in north-central Maine, near its geographical center at: 45º 54’ 16.07” N, 68º 55’ 18.75” W. If you plug the co-ordinates into Google Earth, it will take you there.

Bangor is 75 miles to the southeast, and Boston is another 225. Nova Scotia and the Bay of Fundy are a good 200 miles to the east, and the Canadian border is 60 miles to the northwest towards Quebec.

In 1836, C.T. Jackson began what would become the first field season of what was to become the first report on the geology of Maine. He ascended to the summit of Katahdin and noted that the mountain was comprised completely of granite, and that, based on the erratics on the mountain, believed it was evidence of the Biblical Deluge that had covered the mountain. Water certainly did but not in its aqueous form. Using barometric observations, he calculated the altitude above sea level to be 5,300 feet - only 31 feet off!
From the Maine Geological Survey

Using the simplest definition possible, Katahdin is a steep and tall mountain composed of a large mass of granite that has weathered to the surface over time. Its granite core formed within a cooled magma chamber or batholith below the earth's surface. It's also a pluton - an encompassing term that includes other intrusive (also called plutonic and means formed into older rock below ground) igneous bodies such as stocks, dikes and sills.

When molten magma reaches the surface, it may extrude and flow as lava, or in the case of Katahdin, violently eject outward under tremendous pressure. Small particles of ash blasted aloft and settled on the landscape in the form of a rock called welded tuff when solidified. Rhyolite is the extrusive counterpart of its parent intrusive granite. Thus, rhyolite-tuff describes its chemical composition and genesis-rock, Katahdin granite.

These volcanic events are the result of tectonic plate convergence on the earth's surface, a process that forms continents, closes intervening ocean basins and builds lofty mountain ranges. The tectonic collision that created the magma chamber of Katahdin also built the Appalachian Mountain chain. Of course, this is a basic interpretation. In order to better understand the topography, we must gain an appreciation for the geologic processes that have shaped the region and the east coast of North America for that matter.

Katahdin is Maine’s highest mountain and lies at the northern terminus of the 2,178-mile Appalachian Trail that starts on Springer Mountain in Georgia. A trek on the meandering AT parallels the strike of the Appalachian orogen through 14 states and includes many terrains familiar to historians and terranes to geologists alike - the Cumberlands, the Blue Ridge, Shenandoah, and the Green and White Mountains of New England.

The footpath of the Appalachian Trail from Springer Mountain in Georgia to Mount Katahdin in Maine
follows the strike of the Appalachian orogen.
Map from
Katahdin is the undisputed centerpiece of Baxter State Park - an over 200,000-acre preserve of mountains and valleys generously established by donations of land beginning in 1931 from Percival P. Baxter, a two-time governor of Maine. To protect the area from logging, he personally purchased the land from logging companies and deeded it to the state.

The stipulation was that it remains “forever…in the natural wild state…as a sanctuary for wild beasts and birds that no roads or ways…be constructed therein or thereon.” In Governor Baxter's own words: 

"Man is born to die. His works are short-lived.
Buildings crumble, monuments decay and wealth vanishes,
but Katahdin in all its glory forever shall remain the mountain of the people of Maine."

Baxter Park Rangers fastidiously preserve and protect the park and its hikers, watching the weather closely for safety and disallowing ascents in storms and high winds. The number of climbers are regulated by the number of cars allowed to enter Baxter, so arrive early with an online registration (here). During the recent federal government shutdown, my confirmation call to the park was proudly answered, “Of course we’re open! We’re a state park and independently funded at that!”

Northern Appalachians Ablaze with Color
Beneath overcast skies on our approach to Baxter State Park from the southeast the day before our climb,
Katahdin's summit and those of its neighbors were shrouded in mist. Salmon Stream Lake is in the foreground. 

Recording a billion years of orogenesis, the once Himalayan-comparable Appalachian orogen
extends 2,000 miles from Georgia to Maine and as far as Newfoundland, Canada with buried components beneath the Atlantic and Gulf coastal plains, and the Atlantic continental shelf. Named by the Spanish in the 1500’s for a Native American tribe – the Apalachis - it is an eroded, accretionary orogen and represents the site of long-vanished ocean basins consumed in a collision of a mosaic of terranes with Laurentia - the core of ancestral North America.

Traditional descriptions of the evolution of New England and its Northern Appalachian section include a succession of Paleozoic tectonic events: the Penobscottian, Taconic, Salinic, Acadian and Alleghanian orogenies. The landscapes that these mountain-building events created are manifested by a geological zonation across the strike of the orogen in the direction of their tectonic migration onto and across Laurentia (below).

Unravelling the tectonic history of Laurentia's eastern plate margin has been an arduous and complicated work in progress. That said, let's briefly summarize the orogenic events in order to put Katahdin's regional emplacement into perspective (red dot).

Regional Geologic Map of the Northern Appalachian Orogen from New York to Newfoundland
For orientation, identify the states of New England and New York outlined with a dashed line (also inset lower right). Locate New York State on the far left with its upstate Grenville-age Adirondack Massif and downstate Acadian-age Catskill Delta. The Taconic Queenston Delta lies beneath and imprinted by the Acadian. To the east lies the Appalachian front and the many terranes that were accreted and deformed during the Paleozoic. 
The red dot is the location of Katahdin in north-central Maine within the Piscataquis magmatic belt, an assembly of mafic and igneous rocks of Early Devonian-age (407 Ma). The belt is closely associated with coeval sedimentary rocks of Emsian age.
Modified from Rankin et al, 2007

In the earliest Paleozoic, the fragmented Late Proterozoic supercontinent of Rodinia is represented largely by the megacontinents of equatorial Laurentia, South Hemispheric Gondwana and the micro-continent of Baltica - all sharing the waters of the Iapetus Sea. This was a pivotal interval in the Earth’s history – a time of worldwide orogeny, proposed "snowball" glaciations, rapid continental growth, profound changes in ocean geochemistry, and an explosion of biological activity and early animal radiation (Visit here).

Rodinia's rifted continental elements would re-assemble in succession throughout the Paleozoic and eventually form the supercontinent of Pangaea, create the Appalachian Mountain chain and emplace Katahdin in the process.

Rodinia Shortly After its Fragmentation ~750 Ma
The megacontinent of Laurentia is positioned equatorially. The recently rifted continents, by and large, have not yet reassembled at ~550 Ma australly as Gondwana. Orange represents 1300-1000 Ma mountain belts; green represents continents with paleomagnetic data.

Torsvik, 2003

Equatorial-positioned Laurentia and South Hemispheric-positioned Gondwana in the Middle Cambrian
Laurentia, Baltica, Gondwana and sundry microplates are separated by the Iapetus Ocean. It is at this time that Avalon terranes are rifting from Gondwana.

The Pebobscottian orogeny is in part coeval (time equivalent) with the early phases of the Taconic orogeny (below). It was caused by a collision between the Penobscot arc and the terrane of Ganderia, a widely misunderstood microterrane situated in the periphery of Gondwana across the Iapetus Ocean. It involved back-arc ophiolites that were obducted onto the Gander margin. The composite terrane trends northeast from Northern New Hampshire, across west-central Maine and into New Brunswick, Canada. This subduction-obduction tectonic event occured in the Late Cambrian to Early Ordovician and preceded the Taconic orogeny, whose arc rocks locally overlie it.

After some 150 million years following Rodinia's fragmentation, the world's continental plates began to converge in the early Paleozoic, driven by the incremental closure of their interposed ocean basins. The first was the Late Ordovician Taconic orogeny from Newfoundland to New York. It i
nvolved Laurentia’s collision with an island arc complex upon closure of the intervening Western Iapetus Ocean.

The Taconic allochthon that formed signifies the earliest recognition of the Northern Appalachian Mountains in western New England and southeastern New York State, while a massive clastic wedge was shed westward into a developing foreland in New York, Pennsylvania and beyond called the Queenston delta.

This was the beginning of the replacement of the open seas of the Western Iapetus off the coast of Rodinia with "exotic" continental crust, a process that would end in the northeast with the formation of New England, Maine and the emplacement of Katahdin. 

The Taconic Orogeny
In the Late Cambrian (500 Ma), the elongate Taconic magmatic arc (red arrow) converges on the Laurentian plate's passive eastern shore at the expense of the Western Iapetus Ocean. To the east, the Eastern Iapetus awaits closure with the convergence of the Avalon micro-continent. Note the Panthalassic Ocean (proto-Pacific Ocean) enveloping the remainder of the globe. The State of Maine is somewhere out on Laurentia's continental slope, and Katahdin has not yet formed.
Modified from Colorado Plateau Geosystems. Inc.
From Time Slices of North American Geologic History DVD

The tectonic history of New England during the Paleozoic has been dominated by discussions of island arcs, exotic terranes and compressional events. Recently, an event of crustal extension has been elucidated - the Salinic orogeny. Replete with sedimentation and a mafic intrusive complex, it developed within elements of the Taconic event in central New England to the west during the Silurian. It includes deep-water strata of four basins, two of which are relevant to our discussion of Katahdin: the Connecticut Valley-Gaspe synclinorium and the Central Maine trough in New England and eastern Quebec.

A boundary within the basins implies a change in the depositional setting from an intercontinental backarc extensional setting to a foreland basin as the Acadian wedge approached from the east (black arrow). Other tectonic models have been proposed, but regardless of the process, the Salinic involved rifting or crustal divergence followed by Acadian deformation and metamorphism. 

On the "Regional Geologic Map" above (red dot) and the map below (red circle), note Katahdin within the Piscataquis magmatic (volcanic) belt AND within the CVG and Central Maine basins. Outboard in the direction of the Acadian front to the southeast (diagram below is a rotated perspective) lies Avalon's coastal volcanic belt "proper" of the orogen.

Principal Tectonic Features Map of Maine, Eastern Quebec and Parts Vermont and New Hampshire
Katahdin's location is within the Piscataquis volcanic (magmatic) belt amongst the Lower Devonian flysch and molasse of the CVG and Central Maine basins. Note also the location of Avalonia's coastal volcanic belt.
The direction of migration of the Acadian front is from southeast to northwest (black arrow).
Modified from Bradley and Tucker, 2002.

The third event to shape northeastern Laurentia was the Middle Devonian Acadian orogeny with the closure of the Eastern Iapetus Ocean. It involved the collision of Avalonia – a peri-Gondwanan, rifted terrane - with Laurentia's east margin. It too built a large clastic wedge and foreland called the Catskill delta. In reality, the accretion of the Avalon arc involved several composite subduction zones. The details of its superterranes and geometries of the Acadian event are only partially understood and beyond the scope of this post.   

Convergence of the Avalon Arc
With the Taconic orogen fully developed during the Late Ordovician (450 Ma), the Avalonian and Baltican micro-plates converge upon Laurentia at the expense of the Eastern Iapetus Ocean. With each collision, mountains were built and crust was added to Laurentia - the expanding proto-North American continent. Also note the relative tectonic quiescence on Laurentia's west coast. Its marginal passivity will end when the east coast's tectonic activity ceases. Our planet is a sphere of fixed dimension. Two massive oceans (such as the Atlantic and the Pacific) can not form simultaneously. One forms at the other's expense.
Modified from Colorado Plateau Geosystems. Inc.
From Time Slices of North American Geologic History DVD

The Acadian orogeny finalized the northern Appalachians from the Canadian Maritimes into New England (and the central and southern Appalachians into the Carolinas), and penetrated into, deformed and imprinted the previous Taconic orogen and its foreland. In Maine, it formed the state's highest mountains in a belt that runs from the New Hampshire border on the west through Katahdin and beyond to the northeast, a distance of 150 miles. In New Hampshire, the range continues through the White Mountains to Mount Monadnock in the southwest part of the state. Thus, the Maine Appalachians are mostly Devonian in age - initially Taconic but deformed and elevated in the Acadian orogeny.

Katahdin emplaced during the Acadian orogeny as deformation migrated from the southeast to the northwest. What's more, its curious locus of emplacement relevant to the Acadian subduction zone was within the flysch and molasse of the Acadian foreland, which will be investigated on our climb of Katahdin.   

The Acadian Orogeny
Fully developed by the Late Devonian (375 Ma), the Acadian orogen accreted to Laurentia and deformed the eastern flank of the Taconic orogen. Likewise, Baltica has merged with Avalonia to its south. By this time, the Northern Appalachians have formed and Katahdin has emplaced within northern Maine. Notice Gondwana  (lower right) draws near signalling the formation of the supercontinent of Pangaea.
Modified from Colorado Plateau Geosystems. Inc.
From Time Slices of North American Geologic History DVD

Lastly, the Pennsylvanian-Permian Alleghanian orogeny (Ouachita orogen in southern and eastern Mexico, and Hercynian-Variscan in southern Europe) finalized the Central and Southern Appalachians and overprinted the Acadian orogen by deforming and metamorphosing parts of New England.

The Acadian involved a largely translational, highly oblique, continent-continent collision that closed the Rheic Ocean, sutured western Gondwana to Laurussia (Laurentia and Baltica), completed a Wilson cycle (here), produced the Appalachian Mountain chain and finalized the formation of Pangaea. The multi-phasic, Taconic through Alleghanian, Paleozoic-spanning event is summarily called the Appalachian orogeny.

The Alleghanian Orogeny
By the Early Jurassic (180 Ma), the Rheic Ocean between Laurentia and Gondwana had closed, and Pangaea, having fully formed, had initiated its fragmentation apart. Within the developing rift between North America, and Africa and South America, the waters of the Atlantic Ocean filled the growing void. Roughly concomitant with the initiation of a passive continental margin on Laurentia's east coast, active tectonics initiated on Laurentia's west coast. Rifting apart of Pangaea gave birth to the Atlantic and Pacific Oceans, the modern continents of the Cenozoic including North America, and the Appalachian Mountain chain along the east coast. The red arrow identifies Katahdin within the Northern Appalachians.
Modified from Colorado Plateau Geosystems. Inc.
From Time Slices of North American Geologic History DVD

Following Pangaea's breaking apart, the familiar continents of our modern world took their places across the globe. The Panthalassic Ocean would become the Pacific. Laurentia's east coast became a passive margin, while its west coast became active - the site of convergence. Pangaea's fragmentation left the Katahdin pluton within the region of the Northern Appalachians of Maine, a hundred or so miles from the sea. Voila!

Our plan was to climb Katahdin from the east, where the bedrock is well exposed for observation. It's also one of the best places to view glacial features both on Katahdin's slopes and the valley floor, so we didn’t want to miss the opportunity after having driven over 300 miles from Boston on the previous day. The entire month of October experienced heavy rain in New England, but the forecast for our climb was blue sky. We were elated.

Katahdin from the east
Katahdin looms large from all directions, here from the east outside of nearby Millinocket.
High Dynamic Range photo contributed by resident Mainer FL Doyle III (

Visitors to Baxter State Park are regulated by the number of cars that are allowed to enter. Unfortunately, having arrived only minutes late, the gate attendant gave away our reserved parking space, the last one on Katahdin’s east side. He offered parking on the west side, not our preference, which we readily accepted. Our passing thought (which eventually became our plan) was to ascend from the west and descend to the east. The problem was that it would put us over 20 miles from the car after dark.

Before driving away from the gate, the attendant asked us a curious question, "Got a flashlight?" "Yes", we answered. More on that later. A word to the wise – don’t be late at the gate, or better, camp at the base of Katahdin the night before your climb. And don't forget that flashlight!

Topographic Map of Katahdin
Our route (red arrows) on Katahdin was an 11-mile, west-to-east traverse. Beginning at the trailhead at Katahdin Stream Campground, the progression was up Hunt Trail, across the summit and down by the Saddle Trail to Roaring Brook Campground via the Chimney Pond trail. Click on the photo for a larger view.

At 5,267 feet, Katahdin is the highest mountain peak in Maine, yet it has a local relief of 4,700 feet making it one of the largest massifs (a massive mountain formed of basement or plutonic rocks) in the Appalachian Mountains. There are many routes to the summit of Katahdin, all of which involve some degree of scrambling (using all fours) and all of which are steep and challenging.

We headed out on the Hunt Trail, a popular ascent with outstanding features (far right on Google Earth below). Notice the flat plateau on Katahdin's west side (right), and the collection of cirques on the east side (left). Download trailmaps of Katahdin here.

Google Earth View of Katahdin Looking South

The trailhead is at Katahdin Stream campground, elevation 1,075 feet. It follows the stream on a persistent upslope built on talus through a mixed boreal forest of hardwoods such as white birch and red maple, and evergreens such as balsam fir, red-black spruce, hemlock and white cedar. The ground flora was rich in mosses, ferns, bunchberry and hobblebush. This is an alpine temperature ecosystem of great diversity.

Virtually all of the granite bedrock is related to the time of Katahdin's emplacement - Early, possibly some Middle, Devonian age, although a small region in the park’s southwest corner is Late Devonian. Older Cambrian and Silurian rocks surround the park within the aforementioned basins, attributable to the tectonic and emplacement regime of the Katahdin pluton, of which less than half is within Baxter State Park.

The Ascent Team
Our "ascent team" included my son Will (left) and his friend Leo, both fit as a fiddle and seriously pumped to climb - as one can plainly see. The Hunt Trail is crossing Katahdin Stream on a bridge of logs. Massive boulders of Katahdin granite are everywhere. As the grade increases, the boulders will stack into a near-vertical wall.

The cold October night created a temperature inversion in the valleys around Katahdin. Looking like a large lake off to the west, trapped cold air created a thick foggy blanket that quickly burned off in the sun. Still near freezing, we immediately began shedding layers as the pitch and our efforts increased.

Temperature Inversion Fog

Picturesque Katahdin Falls, at an elevation of about 1,600 feet, spills over a wall of Katahdin granite. The bedrock is homogeneously granitic on the Katahdin pluton, so the knickpoint didn't form on strata of varying lithologies with differing erosion-resistance typical of a sedimentary rock-dominated terrain. Instead, the falls is a consequence of the varying glacial landscape and mass-wasting that was rendered to the region after 12,000 years of erosion. At this elevation, the forest is predominantly red-black spruce and balsam fir that provides a veneer of aromatic and spongy, orange-brown needles everywhere.

Katahdin Falls
The calmness bequeathed here is in contrast to the arduous climb that awaits above.

The boreal forests of Baxter State Park began to develop about 12,000 years ago with the regression of the Laurentide ice sheet. The land retained its tundra ecology for at least 1,000 years as the first human inhabitants left evidence of their presence. As the climate gradually warmed, it had a profound effect on the resident animal population. Northern forests of spruce and fir support relatively little herbaceous vegetation, offering little subsistence for gregarious herbivores like musk ox and caribou that gradually drifted northward out of the region.

Today, 8,000 or so years later, the forests of northern Maine changed from boreal to spruce and fir-dominated. The regional soil is generally poorly to moderately drained over compressed glacial till or areas of shallow soil clinging to the bedrock. A great many of the forests have been harvested for logging, but Baxter is a "gem in the woods" - literally.

Upon gaining altitude, the terrain began to unfold. It was even more clear that Katahdin is situated in an extensive forest of the Maine Wilderness. The stands and bands of bright-orange Sugar Maples in the valleys are growing on alluvially-enriched soils generated by huge glacial meltwater channels from the Pleistocene. As we progressed upslope, the soil-till-talus mix gave way to talus-dominated, and ultimately bedrock sprinkled with weather-fractured blocks of granite. The mosaic of hardwoods and softwoods is evident with the change in autumnal color.

The mountains immediately off to the west of Katahdin have names such as Squaws Bosom, Tabletop, Barren, The Owl and the Brothers. Every one is cored with intrusive granite of the Katahdin pluton. That's not the case north of Katahdin where Traveler Mountain is composed of bluish-gray extrusive rhyolite, yet it's part of the same pluton, or better stated, volcanic complex - a hint at the co-magmatic regime of Katahdin. By the way, Traveler got its name from the early explorers that boated down the East Branch of the Penobscot River since the mountain seemed to travel with them.

Macrolichens of New England
A foliose (leafy) and a fruticose (shrubby) lichen - two of the main types - germinate on a hardwood branch. Exposed rocks, particularly at higher elevations, are covered with the third lichen-type - crustose (crusty).

To the west, beyond the composite of summits of the Katahdin pluton and those of the Piscataquis belt, lies the aforementioned sedimentary, Salinic basin of the Connecticut Valley-Gaspe synclinorium. The extensional trough formed in the Middle Silurian within previously-accreted magmatic arcs of the Taconic orogeny (the Shelburne Falls and Bronson Hills arcs) that separated them. The sediments that accumulated within the trough were overlain by those derived from the foreland of the encroaching Acadian orogen. 

The Migration of the Acadian Front
Map of Maine showing sequential positions of the Acadian deformation front in its migration from the southeast to the northwest. The region of the Katahdin pluton is encircled. Note the time stamps. 
Modified from Bradley and Tucker,2001. 

With the convergence of the Avalon terrane in Late Silurian to Middle Devonian time upon Laurentia’s eastern margin and the trough, the Acadian front and foreland basin migrated northwestward across Maine, adjacent areas of New England, and New Brunswick and eastern Quebec of Canada. With the orogen's advance, it overrode and deformed the earlier Taconic-modified margin and inundated its migrating Acadian foreland basin with clastic successions of Devonian flysch and molasse and blanketed some of the deep-water Silurian sequences that accumulated within the synclinorium.

The landscape we see today records these Silurian and Devonian sedimentary deposits and retains the barely perceptible, synclinal geomorphology of the extensional tectonic regime. But by what tectonic design did Katahdin and the Piscataquis volcanics emplace?

View West from the below the Hunt Spur
The bare granite cliffs to the right are on The Owl. Notice the rockslides on the slopes beyond. Heavy rains saturate the thin cover of soil on steep slopes that are poorly retained on the smooth granite. When they catastrophically fail, steep treeless scars record the event, never to reforest. Also, notice the enigmatic bands of "patterned growth" (Caldwell) or mortality patterns of the spruce and fir in front of the Owl to the far right. Except for elevation, topographical factors are not consistently related to the mortality. A budworm outbreak that reaches epidemic proportions about every 35 years has been implicated. Other hypotheses for the banding include host trees overtopped by hardwood canopies and factors relating to drainage and soil-type.

Volcanic rocks within the Acadian orogen occur in two broad belts: a Coastal belt that erupted into the basement of the Avalon terrane and a second belt of Silurian-Devonian volcanic rocks – called the Piscataquis magmatic (or volcanic) belt within the foreland of New England (and the Tobique volcanic belt in Canada).

Plutonic activity in this part of the orogen was produced by Acadian deformation and falls within a narrow range of the Emsian age of the Devonian (400-410 Ma.). The actual deformation front was south of the Katahdin pluton - placing it within the foreland basin, a location of emplacement that departs from the conventional tectonic norm.

In addition, the ash-flows of Traveler rhyolite on Traveler Mountain to the north of Katahdin AND Katahdin itself are regarded as the volcanic and plutonic parts of the SAME igneous complex. In fact, the granite intrudes the rhyolite (on the north ridge of Wassataquoik Mountain and on the southern slope of South Traveler Mountain both to the north of Katahdin). The rhyolite-granite contact has been Zircon dated at 406.9 ± 0.4 Ma, which sets the maximum age for the granite. 

The emplacement of the Katahdin pluton likely occurred at shallow depths because of the presence of the granophyric phase of granite and because the granite intruded its cover-carapace of rhyolite. Violent, successive eruptions at the surface spewed thick volcanic ash that flowed over the region preserved in the welded tuff of Traveler Mountain. If the carapace of Traveler rhyolite that once covered the likely caldera of Katahdin (formed when the volcano's magma chamber collapsed within itself), then the Katahdin volcanic complex would qualify as among the largest volcanic features known in the world (Hon, 1976). One can only imagine what this place was like during the Early Devonian!

Geologic Map of the Katahdin Region
Less than half of the Katahdin pluton is within Baxter State Park. Oval in outline and elongated in a NE-SW direction, it is roughly 40 X 22 miles and perhaps 3 miles thick. To the north the pluton is overlain by the Traveler rhyolite.
Modified from Bradley and Tucker, 2001.

Dating and geologic mapping have arrived at the conclusion that the upper parts of the Katahdin pluton are close to the roof of the magma chamber of the Katahdin granite and that the roof or carapace slopes north toward Traveler Mountain. We will see this in the phases of granite that crops out at various elevations on our climb. Where's the ash that we assume once covered Katahdin? It eroded away in the roughly 400 hundred million years since it blanketed the region, at a rate estimated at 20-100 feet per million years (Judson and Ritter, 1964). What's left of the ash comprises the rhyolite-tuff in the region of Traveler Mountain to Katahdin's north, all that's left of Katahdin's carapace.

An Emsian-age transect (below) through the orogen in the Katahdin area shows the plutons emplaced into already-deformed Devonian rocks at a depth of 6.5 km. At this time, Katahdin is envisioned to entertain both "volcanism at the surface and plutonism at depth." (Bradley and Tucker, 2001). Emsian magmatism originated within and beneath the orogen BUT were extruded across the deformation front into the foreland. According to Bradley and Turner, "Although these younger plutons are commonly referred to as "Acadian," they postdated the documented cratonward advance of the deformation front and so cannot be linked to Acadian plate convergence."

Nonpalinspastic Map of Maine
Sequential positions of the Acadian deformation front are shown with dates as it migrated (arrow) across Maine (find borders of the state for orientation). In the Early Emsian (~407 Ma), the Katahdin pluton emplaced within the Acadian foreland. During this ~40 million year interval, the front is thought to have advanced some 240 km cratonward.
Modified from Bradley and Tucker, 2001.

The calc-alkaline, subduction-related granites likely possess a mantle component. The magmatism "cannot be solely a consequence of collision-induced thickening of continental crust" (Bradley and Tucker). One interpretation of the Katahdin-Traveler system is that mafic magma, generated deep within the mantle, ascended perhaps 20 miles from the surface beneath the crust (diagram below). Heat from the ponded magma partially melted the crust, generating a granitic magma. As the magma continued its buoyant ascent, it cooled and crystallized, accumulating gases within the upper chamber. The gas-rich magma escaped to the surface in a series of violent eruptions generating the
successive ash flows of the Traveler rhyolite.

Cross section through the Acadian Deformation Front during Early Emsian Time in the Katahdin Region
From Bradley and Tucker, 2001.

The volume of rhyolite that was produced is estimated to have been 80 cubic miles 
compared to less than 1/10th of a cubic mile in the devastating 1980 eruption of Mount St. Helens. Typically, large extravasations of rhyolite lead to caldera formation with a rapid evacuation or pressure release within the magma chamber. It's likely that Katadin experienced some caldera formation, since some components of the Traveler rhyolite (Black Cat Member) demonstrate compaction foliation and faulting. Clearly though, the caldera-like geomorphology of Katahdin is the product of erosion following its exhumation.

Unfortunately, I have no photos taken from within the Spur - a hundred feet or so of near-vertical, jointed granite. I admit that I was more concerned with safety than photography. However, I borrowed this photo from the web to illustrate my point.

"What am I doing up here?" nicely sums up the Spur

Leo and Will rejoice from the top of the Spur. Notice the Katahdin granite is now pinkish and blanketed by a black and yellow-iridescent lichen, largely Lecidea geographica. Eight distinct lichen habitats of almost 300 species have been found on Katahdin from its subalpine forests through the krummholz to the exposed alpine tundra at the summit. Lichens are sensitive to elevation, climate and air pollution. Bryophytes (liverworts and mosses) are also abundant - over 200 species.

In the distance, the chain of post-Pleistocene lakes are within the Maine Wilderness Area. In the lowlands, orange Sugar Maples are sharply demarcated against evergreens that are thriving on nutrient-rich alluvium deposited during glacial melt.

Atop the Spur
Leo and Will rejoice at the top of the Spur.

At about 3,850 feet, we're entering the Gateway - a ridge of boulder-strewn bedrock that leads to the flat plateau of the Tableland. Having negotiated the Spur we expected to have a glimpse of the summit but were surprised by the size of the Gateway. We were amused by descending climbers who exclaimed, "You're almost there!" - when in reality, there's another 4 miles to the ultimate summit of Katahdin! 

We're clearly above the treeline. At this elevation, growing conditions have become increasingly severe with scarce nutrients, poorly drained, thin residual soils, wind, exposure and prolonged cold. Mineral soils have given way to organic soils. Most 
herbaceous plants and tall trees can't tolerate these conditions. This is the sub-arctic krummholz or "crooked-wood" zone, dominated by tangled and stunted balsam fir, many in close stands that are almost impenetrable.  The krummholz transitions to the alpine zone once on the Tableland.

At first glance, the plantscape appears uniform, but close observation shows a mosaic of 
mosses, lichens and dwarf shrubs of fir, juniper and spruce. Microclimates and flora vary with the topography - expanses of bare bedrock, areas with thin soil and sheltered depressions out of the wind. You can tell the prevailing direction of the wind by the distorted shrubs that draw to the left.

The Gateway to the Tableland
The Gateway is a huge boulder-strewn ramp to the flats of the Tableland. That's Will, now wearing green, and Leo in black above him. The clouds are rolling in from the southeast (right) and dropping down into the cirque to the northwest. We experienced a sense of climbing into the "unknown." Further off to the right is the dangerous, steep and loose trail of Abol Slide, which also summits Katahdin from the west. 

Katahdin's granite occurs in two phases. The variety that forms the core and most of the pluton is the granitic phase. Largely light gray and homogenous, its an equigranular (uniform), medium-grained granite. Compositionally, the granite is 33% quartz, 33% alkali feldspar, 25% plagioclase, 5-10% biotite and accessory minerals.

As one ascends Katahdin, a gradual transition occurs from the light gray granitic phase at lower elevations, through mottled white and pink to salmon, and finally to brick red of the granophyric phase near the top of the pluton. The red comes from grains of hematite (iron oxide) contained within crystals of alkali feldspar. The color change is accompanied by higher percentages of fine-grained quartz and alkali feldspar that surround larger crystals with interlocking crystals. The geometric patterns one sees are typical of porphyritic igneous rocks and also contain small vugs (cavities).

The coarser-grained granitic phase is thought to have cooled more slowly allowing for crystal growth, being closer to the interior of the magma chamber, than the granophyric phase, that cooled more rapidly being closer to the colder bordering rock. Water-rich gas bubbles near the roof of the chamber were trapped by the rapidly cooling granophyric phases.

The Two Phases of Granite within the Katahdin Pluton - Granitic and Granophyric
In these specimens photographed on Katahdin, one can readily identify white feldspars,
black biotites and gray quartz.

Parallel sets of through-going planar cracks or joints that develop in the granite fuel the mass wasting process that sends boulders downslope. It will eventually level Katahdin to a peneplain - the fate of all mountains in time. On the Tableland and scattered across Katadin's summit, the bedrock is broken into scattered boulders on the summit.

The body of granite can also form joints from contractional cooling and from the strain induced by continent-deforming tectonic processes. Exfoliation or sheet joints are found on steep planar surfaces such as found on the walls of glacial cirques. They are formed more recently by unloading as the weight of the overburden is removed by erosion and the melting of glacial ice. Once formed, granite sheets can be further truncated by erosion as freeze-thaw cycles and gravity pry off the surface and fill the floor with talus debris.

Transitioning from the Granitic to Granophyric Phase of the Katahdin Granite on the Gateway
White blazes of paint and small cairns mark the trail. Notice the blanket of black and green lichens that cover the granite and its increasingly salmon color.

Higher on the Gateway, Will forges ahead into the clouds that are streaming up from the cirque on the south face of Katahdin. Rainbow-colored curtains of water vapor shimmer in the wind. A gauntlet of lichen-speckled boulders are thrown everywhere in contrast to the tundral vegetation displaying fall colors. Incredibly beautiful. You want to stay, but the summit beckons. So does nightfall, as we carefully watch the time.

Halfway up the Gateway
Massive boulders litter the bedrock of the Gateway. "Almost on the plateau!"

Off to the right are Mount Coe and South Brother. The lowlands to the left (west), 
blanketed in colorful hardwoods, drape away from the Katahdin pluton onto till-covered Early Devonian, Ordovician and Silurian sedimentary rocks.

Will clears the Spur onto the flat of the Tableland

The southern region of the Katahdin massif is a broad, open, treeless, weather-exposed, gradually sloping plateau to the peaks that lie on the edge of the cliff-rimmed basins. Weathered blocks of bedrock were strewn everywhere, virtually coated with iridescent green-yellow lichen illuminated by the sun.

The plants of this arctic zone at this altitude have evolved to tolerate the extreme environmental conditions. Grow low is the dominant survival tactic, but everything from shallow root systems to desiccation-resistant leaves contribute to their ability to thrive in this fragile habitat. Although alpine grasses exist, most herbaceous grass can't survive at this elevation and are mostly sedges. Lichens and mosses are also found in abundance. Climbing a high peak such as this is equivalent to traveling north to the arctic in terms of both the flora and fauna encountered. Many of the plants here are rare or endangered, and are protected by a cobble-lined trail to prevent trampling.

View to the northwest from the Tableland
The sign welcomes hikers to the Tableland.

From the same location in the above photo on the Tableland, we're facing north. The peaks of Katahdin's summit appear to be nothing more than a long trek that ends on a plateau, which is what it is. But looks are deceiving in that the east face, which we can't yet see from here, is sculpted beyond anything imaginable. Also blocked from view, rhyolite-built, co-magmatic Traveler Mountain is 13 miles due north beyond Katahdin. We're nearing the top of the magma chamber that is Katahdin!

From the Tableland, we're looking due north across a deep ravine that is the Katahdin Stream watershed. The flat-appearing, bare summit to the far right is Hamlin Peak, one of five that comprises Katahdin.

Looking down from the Tableland to the Gateway, here's a last look at the tabular 
landscape to the west. The "cloud factory" on Katahdin's south slope is still highly productive as the cool rising valley air meets the warmer air aloft. Our climb that began just above freezing is now a balmy 60 degrees.

Several theories have been offered to explain the origin of the broad upland surface of the Tableland including erosional peneplanation and bevelling by glacio-peneplanation. The Tableland consists of resistant granophyric granite identical to that of Katahdin's summit. This resistant caprock in many ways is analagous to a sandstone overlying an erodable shale. Thus, the granophyre "holds up" or protects Katahdin. Once removed, rapid slope retreat occurs and decline into the hills and lowlands of the granitic phase around the pluton.

From the same perspective looking due north (below), we're viewing Hamlin Peak (4,751 feet) to the right across the Northwest Plateau and Basin at the summit of Katahdin. Typical of glaciated terrain in the north, notice the glacial plucking on the south, leeward outcrop of granite. Viewed from the west, the plateau has a roche moutonnee or "sheep-back" configuration with a gently sloping, north face. Our view of Traveler Mountain is blocked by Hamlin peak. To the right are Fort Mountain and North Brother. Our destination of Baxter Peak is to the right (out of view) about 1.4 miles.

We're near Thoreau Spring. Whether or not he actually reached this area is unknown. It is known from his journal that he never reached the summit of Katahdin, having been determined by bad weather. The Tableland is notorious for high winds and pelting rain and snow.

In 1924, Governor Baxter lost his Republican party's nomination to Owen Brewster. While in office, Governor Brewster climbed and erected a plaque at the site of the spring as the first "sitting" governor to climb the edifice. Called Governor's Spring, he used photos of his climb to promote his proposal to convert the region to a national park. Baxter defeated the proposal and in 1933 purchased the first parcel of land of what would eventually become Baxter State Park. Of course the Governor's Spring plaque was replaced with one that reads Thoreau Spring - whether or not he was actually there. So the story goes. 

After 5 hours of climbing, our efforts were rewarded with an unmatched view from the east side of Katahdin. Everything in sight is a compendium of a billion years of geological evolution - Rodinia's fragmentation, Paleozoic plate convergence, the closure of two oceans, Acadian deformation, Katahdin emplacement, the rifting apart of Pangaea, hundreds of millions of years of landscape erosion and exhumation, and finally, Pleistocene glaciation.

Facing northeast from Baxter Peak, the glacial tarn of Chimney Pond lies 2,775 feet at the foot of the ice-carved, semi-circular cirque of South Basin - formed by erosion of an alpine glacier. With the cessation of glaciation, erosion has continued the process of excavation via mass-wasting and repetitive freeze-thaw cycles. Further out on the forest floor of glacial outwash and till, North and South Basins, also tarns, have been impounded by the Basin Ponds end moraine. In the middle distance, North and South Turner Mountains are separated by a glacial U-shaped valley. Rhyolite-composed Traveler Mountain, the co-magmatic partner of Katahdin, is in the clouds at the extreme left.

Photographic documentation of our ascent to the summit of Katahdin! We're standing on weathered blocks of granite, although bedrock crops out just below the summit. On the far side of the sign is a 2,000 foot drop off to the valley below.

Well done, Will!

Leo and Will's turn in front of the lens!

This photo says it all.

This tablet on the summit of Mount Katahdin was placed on March 16,1932 to record the "gift and conveyance" of nine square miles of land to the State of Maine by former Governor Percival P. Baxter, made upon the express condition that the tract "forever be left in the natural wild state."

Notice the salmon color of the granite. It is estimated that the roof of the pluton was only a few hundred feet above this spot. Also, observe the weather fractured cobbles, boulders and grus (coarse-grained sand and gravel resulting from the granular disintegration of the granite from mechanical and chemical weathering) that cover the summit. Even lichens contribute to the insidious dissintegration of the granite by secreting organic acids.

The Knife Edge Trail (blue paint blazes) traverses the apex of a serrated arête that runs the mile or so between Baxter and Pamola Peaks. The north side of the ridge is formed by the glacial cirque of South Basin, while the south side, which likely was sculpted by the Laurentide ice sheet, doesn't bear the classical cirqued-features of alpine glaciation. The south side of the arête may be a greater victim of mass wasting and frost-shattering. Therefore, calling it an arête, which technically requires carving from alpine glaciers on both sides, may not be totally correct.

That said, nothing detracts from the massivity of the ridge and the focus climbers must maintain while negotiating its exposed sections that are merely two feet wide in some areas and plummet some 2,000 feet in either direction. This is probably the most spectacular mountain trail in the East. High winds can be unpredictable and extremely menacing here. The Baxter State Park website posts the warning "Not for the faint of heart!"

This photo faces east from Baxter and illustrates how the Knife Edge curves to meet Pamola Peak. If you click on the image to enlarge it, you'll see numerous hikers balancing their way across it.

The Knife Edge

From the same perch on Baxter Peak, we're looking south into the "cloud factory" of Katahdin's south face that we experienced earlier on the Gateway and the Tableland, which slopes off to the right. The Knife Edge begins off to the left. Notice the extent of weather-pulverized rock that litters the summit that completely blankets the bedrock.

South-facing view from Baxter Peak

The Knife Edge is rather blunted in this early section and covered by large boulders of Katahdin granite. At the far left in the sun, heavily-jointed, granophyric Katahdin bedrock is exposed at the top of South Basin's headwall and throughout most of the arête. Again, notice the climbers for scale. I counted 11 in the photo.

The Knife Edge as it strikes east from Baxter Peak

The Pleistocene epoch began in North America about 2.58 million years ago - traditionally referred to as the first of the Quaternary Period. Over this relatively short span of time geologically, the landscape of North America in Canada and the United States was dramatically altered by at least four phases of glaciation by an up to two-mile thick, slow-moving ice sheet called the Laurentide. Driven by vacillations in the climate, a multitude of glacial advances and regressions (glacial and interglacial episodes) occurred, the most recent of which is the Wisconsinan that extended to about 38 degrees latitude.

Extent of Pleistocene glaciation at 18,000 years ago.
Note the depth of the continental ice sheet in meters. Katahdin is at the red dot.
Modified from A. McIntyre, CLIMAP Project, Lamont-Doherty Earth Observatory, 1981.

Following Katahdin's emplacement in the Early Devonian, hundreds of millions of years of erosion worked to remove nearly two miles of overburden that buried the pluton. Looking back about 10 million years, we would likely see that the general features of the landscape in Baxter State Park were likely already fashioned. Once exhumed, Pleistocene glaciers began to sculpt Katahdin's modern landscape out of its granite.

The Laurentide ice sheet flowed southeast across Maine and terminated at Georges Bank (a submerged area of the sea floor between Cape Cod and Nova Scotia) at a time when the level of the seas was 300 feet below present during glacial maximum. The oceans reached their modern level about 3,000 years ago and of course are on the rise - this being an inetrglacial epoch of warming called the Holocene - the most recent time frame of the Quaternary.

Enough water was held in continental ice sheets during the Pleistocene to lower sea level worldwide by about 150 meters. When deglaciation and the ice age finally ended about 12,000 years ago, the ice sheet left the landscape of Katahdin and the surrounding lowlands with a distinctive array of erosional and depositional landforms in what is a textbook study in glaciomorphology. Few places in the northeastern United states offer a chance to see these features in such an unspoiled setting. Some 400 million years of surface erosion and post-glacial isostatic rebound have allowed the landscape to assume its present attitude almost a mile above sea level. 

Sandy Stream Pond and Katahdin
Sandy Stream Pond is one of the best places to see moose at sunrise or sunset. In the distance, Katahdin’s four cirques and five summits are dusted in late October snow. The low, elongate ridge beyond the treeline is the Basin Pond moraine that dams the Basin Ponds.
Panorama contributed by resident Mainer Donny Doyle (

North view of the Basin Ponds and the Basin Ponds moraine
The Google Earth vertical exaggeration is greatly increased in order to visualize the Basin Ponds moraine that impounds three tarns at the foot of Great and South basins.

Perhaps the most puzzling question concerning Katahdin’s glacial history was whether there was cirque glaciation on Katahdin following the retreat of the continental ice sheet of late Wisconsinan time or perhaps even whether alpine glaciation preceded the arrival of the ice sheet. A second question is whether Katahdin was a nunatak (an Inuit word) with its summit remaining isolated from glaciation.

Glacial erratics found on Katahdin in addition to polished bedrock and striations indicate that Katahdin was in fact once covered by the last advance of the Laurentide ice sheet during Late Wisconsinan glaciation between about 25,000 and 12,-13,000 years ago (Davis, 1989). That disproves the hypothesis that Katahdin remained a nunatak during continental glacial advance (at least during the late Wisconsinan glacial maximum). On the other hand, arguements against the nunatak explain why the serrate topography such as the Kinfe Edge appears so fresh. The controversy that remains is whether the alpine glaciers persisted in the cirques after the ice sheet retreated to the north.

I photographed this quartz-veined metamorphic rock high on the slopes of the Hunt Trail of west Katahdin. This small erratic is a confirmation of the glaciers that once covered at least a portion of Katahdin.

In the past, many (including Caldwell, 1959) felt the cirques and arêtes were too fresh to have been ice sheet overridden and therefore shaped by alpine glaciers. More recently, it has been suggested that the continental ice sheet covered Katahdin but post-glacial mass wasting controlled by vertical jointing of the bedrock shaped the cirques and arêtes (Davis).

Two scenarios are being entertained today. Caldwell envisions a "two-glacier" history - ice sheet followed by alpine glaciers. He interpreted the Basin Ponds moraine to be a medial moraine between alpine glaciers flowing from the east-side cirques and a tongue of the ice sheet flowing between Katahdin and the Turner Mountains to the east. Davis, on the other hand, hypothesized the continental ice sheet was the final glacial activity on Katahdin and interpreted the Basin Ponds moraine to be a recessional-lateral moraine of the waning ice sheet between Katahdin and the Turner Mountains. Clearly, the Basin Ponds moraine is the most controversial glacial feature in Baxter State Park.

As we descended from Baxter Peak across the Tableland, the Saddle Trail can be seen below winding along on the low-lying, flat-topped ridge called the Saddle. The Saddle Trail traces the rim of the Great Basin before abruptly heading down the cirque on a precariously steep and loose rock slide from an avalanche that occurred during the winter of 1898-1899. Avalanche scars are common on Katahdin's steep slopes such as the Y-shaped one in the photo. Rockfalls are common as well on the cirque walls, weakened by joints and freeze-thaw action. 

The Saddle
Coming off the rubble-covered Tableland from Baxter Peak, the Saddle Trail dips into the Saddle.

The surface leading to the Saddle is literally covered with weather-pulverized cobbles of granite with larger boulders peppered here and there.

Weathered and frost-shattered granite literally painted with lichen on the Saddle

Bright yellow-green and black lichens on the red granophyric phase of Katahdin granite were a feast for the eyes.

We're looking back at Baxter Peak from the beginning of the Saddle, as we entered the densely packed and stunted trees of the krummholz zone. There are almost 50 people celebrating their ascent on the summit of Baxter, but you'd never know it from here. One group opened a bottle of champagne to toast their accomplishment.

Glancing back at Baxter Peak, once we cometh, from within the krummholz

The Saddle Trail strikes a rock-hopping path through the krummholz on large boulders of weathered granite. That's Will in the green shirt picking his way down. The landscape pitches to the right in the direction of the cirques.

Krummholz zone of the Saddle

The first portion of the Saddle Trail is appropriately called the Slide on the start of Great Basin's headwall. The going is slow on thin, steep ledges and loose slide material. Cathedral Ridge and Trail are in the middle distance - an arête that separates Great Basin from South Basin. The three knobs on the trail are the "cathedrals" formed by the erosion of porphyritic granite that has been sectioned by vertical joints. Triangular-shaped Chimney Pond is at the base of South Basin at the foot of the headwall that rises to Pamola Peak in the clouds. As one progresses downslope, the red granophyric phase of granite gradually transitions back to the light gray granitic phase, the reverse of what we saw on our west side ascent.

By way of review, every feature in immediate view is composed of intrusive, Devonian-age Katahdin granite with the exception of the more easily eroded sedimentary rocks of the lowlands. The volcano's carapace of extrusive tuff-rhyolite has been eroded away in the process of its exhumation with the exception of Traveler Mountain.

Surprisingly, the majority of the granites in Maine don't form mountains. The multi-phasic structure of the Katahdin granite - the granophyric phase in particular - is responsible for building the high mountain edifice, or better stated,  preventing its erosion. Finally, glaciers of the Pleistocene are responsible for the extreme topography, and its erosional and depositional features and landforms.

For another perspective of South Basin, here's a Google Earth view from the middle of the Saddle Trail, which we descended in the above photo. The caldera-like morphology of Katahdin is a consequence of glacial erosion, mass wasting and freeze-thaw action, although some calderic collapse was a likely occurence during Katahdin's post-emplacement history. The U-shaped bowl of South Basin is framed by the arêtes of Keep Ridge on the left and Cathedral Ridge on the right - created by the action of alpine glaciers excavating both sides of the ridges. At the top of the headwall, the Knife Edge runs from Pamola to Baxter Peak.

In the distance (below), Upper and Lower Basin Ponds are dammed by the Basin Ponds moraine just beyond them - the puzzling feature that we discussed. The moraine stretches nearly three miles and has as much as 50 feet of relief. Its largely consists of granite in all sizes, some up to 20 feet  across. It's noteworthy that Davis (mentioned earlier) found that 10-44% of its rocks were non-granitic - in keeping with his only an ice-sheet-conclusion. Davis further pointed out that the ridge of the moraine is convex westward - a curvature opposite to what one would expect from alpine glaciers that might have originated from the west on Katahdin. What's your interpretation? No Biblical Flood theories please.

The ephemeral Dry Pond in the foreground is water-filled. Beyond, Whidden and Sandy Stream Ponds are almost hidden in the forest before the slopes of South Turner Mountain.

Subglacial sediment transport as debris-rich ice were deposited as meltout till, but other depositional landforms exist as well in Baxter State Park. While a large drumlin-field exists in southern Maine, the Katahdin esker system consists of a sinuous, branching network of poorly-sorted sand, gravel and boulders that stretches 150 km from its source near the entrance to Baxter State Park just south of Katahdin to its terminus at Pineo Ridge near the Maine coast. These glacio-depositional landforms were left in the wake of the receding ice sheet.

Eskers are constructed by subglacial streams and rivers flowing within ice-walled tunnels along the glacier bed. Their resemblance to long-abandoned railway embankments led Maine old timers to humorously refer to them as "Indian railroads." In fact, some rural roads in the area are built along the crest of an esker.      

The Basin Ponds, Dry Pond and the Basin Ponds moraine
The setting sun on the opposite side of Katahdin is casting long shadows across the valley.

Perched on a thin ledge of the Saddle Trail, the view was unmatched. That's Katahdin Lake in the middle distance. The Canadian border between eastern Maine and the province of New Brunswick lies 55 miles due east, and Nova Scotia and the Bay of Fundy is another 160 miles.

For the record, the Bay of Fundy lies in a rift valley called the Fundy Basin. The rift began to form when Pangaea began to break up in the Late Triassic. The formation of the Atlantic Ocean placed Katahdin and the entire Appalachian Mountain range within reach of the sea along North America's east coast.

View from the Saddle Trail of the glacial valley at the merging of the foot of the cirques

Vertical-jointed granite on the knobs of Cathedral Trail stand out in profile. Beyond, Pamola has briefly emerged from the clouds. The notch to the right of the peak is the ridge-crest manifestation of the Chimney, a northwest-trending fault zone of highly fractured rocks that continues to the foot of the cirque as a steep, narrow gully or couloir. The Chimney is a popular challenge for technical climbers heading to the Knife Edge.

Pamola Peak and the Cathedral Ridge in profile from Saddle Trail

From the Ranger Cabin at Chimney Pond, the impressive semi-circular headwall of South Basin dominates the frame. The sun was very low on the horizon on the far side of Katahdin. You can make out curtains of granite that are exfoliating from the headwall.

Eight or nine recognizable cirques surround Katahdin with the exception of its south flank. The three largest are on the east side of the mountain. Why are the east-facing cirques larger than the others? One explanation is that prevailing northwest winds blow snow to the largely sun-sheltered east-side cirques. A similar prevailing climate during the Pleistocene would have encouraged the cirque-size disparity.

The sheer headwall of South Basin

From the water-filled Dry Pond seen from above, we're looking back at the base of the Cathedral and Great Basin beyond. Wet Pond is an ephemeral tarn that is subject to the whim of precipitation from the watershed of South Basin. Outwash deposits from meltwater streams blanket the region as do erratics of all shapes and sizes.

A not-so-dry Dry Pond

Pamola, the bad-tempered, winged deity of Katahdin, was good to us. Our west-to-east traverse was a resounding success and an invigorating experience in terms of the geology and the fun we had. Our 10-mile expedition took 11 hours to complete. The only problem was that our car was over 20 miles away on the opposite side of the mountain. Having arrived in the valley and forest wilderness after dark, we more fully appreciated why the gate attendant asked if everyone was carrying a flashlight. Fortunately for us, it was a brilliant full moon, and we didn't even need one.

Our plan to hitch to our car was totally unsuccessful in that virtually none were leaving the Roaring Brook campground. Fortuitously, a conversation we struck up with a Search and Rescue Ranger on the trail resulted in him radioing ahead to the Park Ranger, unbeknownst to us, who picked us up on the forest road and gave us a lift back to our car.

That's Leo and Will in the back of the Ranger's pickup. Thank you Baxter Park Rangers and Governor Percival Baxter for making it all happen. What a great day!

"What you get by achieving your goals is not as important as what you become by achieving your goals."
Henry David Thoreau

A Guide to the Geology of Baxter State Park and Katahdin by Douglas W. Rankin and Dabney (Dee) W. Caldwell, Maine Geological Society, 2010.
Baxter State Park and Mount Katahdin - Trails Illustrated Topographic Map, National Geographic, 2011.
Emsian Synorogenic Paleography of the Maine Appalachians by Dwight Bradley and Robert Tucker, The Journal of Geology online, 2001.
Foreland-forearc Collisional Granitoid and Mafic Magmatism Caused by Lower Plate Lithospheric Slab Breakoff: The Acadian of Maine, and Other Orogens by A. Schoonmaker et al, Geological Society of America, 2005.
Guidebook for Field Trips in North-Central Maine, 105th Annual NEIG Conference, 2013.
The Geology of Baxter State Park and Katahdin, Bulletin 43, Plate 1 - Bedrock Geology and Plate 2 - Surficial Geology, 2010.
Roadside Geology of Maine by D.W. Caldwell, 1998.