Geology is all around us, scarcely thought of as we go about our lives. Yet, it affects everything we do as a civilization, as a society and as individuals. While barely appearing to change from day to day, it works to alter the course of evolution. Preserving a record of creatures and landscapes both ancient and forgotten, the story of our past is written in stone and waiting to be read. I offer a view of how I see our world and its inhabitants, both past and present, as seen through my lens.
Friday, September 30, 2011
Flight Plan: Part II – Geology of the Circle Cliffs Uplift and the Waterpocket Fold at Capitol Reef National Park
The Waterpocket Fold is the centerpiece of CapitolReefNational Park in Utah.
This post is the second in a series of three on my recent aerial investigation of the geology of the San Rafael Swell, the Circle Cliffs Uplift at CapitolReefNational Park, and the HenryMountains, all in southeastern Utah. The first two landforms are massive, domal uplifts that formed during the Laramide Orogeny. The HenryMountains are a laccolithic complex of mountains that formed later during the Oligocene and Early Miocene.
TAKING TO THE SKIES TO STUDY THE GEOLOGY ON THE GROUND
In May, I traveled through Utah’s backcountry to investigate the geology with my friend, geologist and author Wayne Ranney (WayneRanney.com). It’s difficult to fully appreciate the scale and geological relationships of many of the Colorado Plateau’s massive landforms on the ground. An aerial view of the landscape provides an unparalleled, big picture-perspective and some beautiful photos as well.
OUR FLIGHT PLAN
Our roundtrip flight began in Price, Utah, and followed CastleValley to the south between the Wasatch Plateau to the west and the San Rafael Swell to the east. Eventually, turning to the east, we traced the course of the San RafaelRiver as it dissected its way though the canyons of the Swell directly across its domal crest. We emerged at the Swell’s monocline, the San Rafael Reef, and again turned south to follow its strike, Part I of our flight. Continuing southward, we pursued the Circle Cliffs Uplift and its monocline, the Waterpocket Fold at CapitolReefNational Park. Our plan was to investigate Capitol Reef in the same manner by flying west to east across the uplift and then turning south to follow its monocline, the subject of this, Part II of our flight.
AN INCREDIBLY ABBREVIATED GEOLOGICAL BIG PICTURE OF SOUTHEASTERN UTAH
The geological history of the Circle Cliffs Uplift and the Waterpocket Fold essentially encompasses that of southeastern Utah, as well as much of the Colorado Plateau. Regional stratal differences in the vicinity of Capitol Reef exist, many of which were identified during our flight. In all, Capitol Reef has experienced seventeen formations (and almost as many members) ranging in age from Permian in the west to Cretaceous in the east.
Ron Blakey’s fantastic paleomaps (http://cpgeosystems.com/index.html) are a tremendous help in understanding and visualizing the Southwest’s complex depositional environments. His book co-authored with Wayne Ranney, Ancient Landscapes of the Colorado Plateau, “brings the past alive like never before.” This book is an indispensible reference in my library.
PRECAMBRIAN FOUNDATIONS, ANCIENTPALEOZOICSEAS AND ANCESTRAL MOUNTAIN RANGES Numerous Precambrian continental accretionary events assembled the basement rocks on which subsequent early and middle Paleozoic marine sedimentary units were deposited in western North America, on the Colorado Plateau, and in the region of the Capitol Reef. In the late Paleozoic during Pennsylvanian time, the Ancestral Rocky Mountains were responsible for both marine (Hermosa) and alluvial to shallow-marine (Cutler) sediments in a large area, including eastern Utah.
During the Permian, Kaibab seas were the last of the Paleozoic marine waters to invade the Southwest, which covered most of Utah with the exception of the White Rim Sandstone in the southeast. Utah experienced marine incursions during earlier Pennsylvanian time within basins associated with the Ancestral Rocky Mountains, and later in the Mesozoic with the MiddleJurassicSundanceSea that transgressed from Wyoming, and the Western Interior Seaway during the Cretaceous that rose from the east.
Stratigraphic Column of Capitol Reef
(Modified from CapitolReefNational Park and Vicinity Geologic Road Logs, UGA,2004)
TRIASSIC FLOODPLAINS, SWAMPS, LAKES AND BRAIDED RIVERS
During the Early Mesozoic, Triassic-age floodplain-fluvial-shallow marine and floodplain-lacustrine-fluvial sediments (Moenkopi and Chinle Formations, respectively) blanketed the region with siltstones, sandstones, shales and mudstones from southern and southeastern sources.
JURASSICSANDSEAS, A MARINE INCURSION AND CONTINENTAL DEPOSITS
Early Jurassic-age windblown sandstones (the Glen Canyon Group’s Wingate and Navajo) became the prevailing sedimentation with interposed and interfingering fluvial and eolian deposits (Kayenta Formation). During the Middle Jurassic, a marine incursion called the SundanceSea (Curtis-SummervilleSea) repeatedly advanced and retreated into Utah from Wyoming. As the sea waxed and waned, the San Rafael Group's deposits interfingered and varied (eolian Page Sandstone, Carmel Formation mudstones and sandstones, eolian Entrada Sandstone, and Curtis and Summerville Formations' siltstones and sandstones). By the Late Jurassic, mountains generated by the Nevadan Orogeny to the west saw the vari-colored Morrison Formation spread its fluvial and floodplain deposits to the east over a widespread area, and then followed by the Cedar Mountain Formation. Continental deposition remained dominant for 100 million years thereafter.
CRETACEOUS COLLISIONS, UPLIFT AND A VAST INLANDSEA
Beginning in the latest Jurassic and continuing throughout the Cretaceous into the Eocene, the oceanic Farallon Plate subducted beneath the continental North American Plate at its western margin. That tectonic collision initiated two continuous and overlapping, but one-prolonged mountain-building event (Sevier and Laramide Orogenies). Although both orogens possessed east-directed compression, they are distinguished by their differing modes of deformation. The driving force of Laramide deformation stretched eastward 1,500 km.
Farallon subduction profiles during the Sevier and Laramide Orogenies
The most severe zone of deformation formed the backbone of the modern Rocky Mountains and further imprinted the Sevier downwarping (foreland basin) of the craton. Thus, the expansive Western Interior Seaway formed which received sediments from the mountainous front to the west. The Seaway extended throughout the contemporary Great Plains and many western states including eastern Utah, and from the Arctic to the Gulf of Mexico. Coevally, mid-ocean ridge activity in the Pacific, with its hot, buoyant crust, elevated the ocean basin's floor and displaced huge volumes of seawater. Subsequently, global sealevel rose which spilled onto low-lying worldwide landmasses. That served to further expand the confines of the epicontinental seaway. Numerous transgressions and regressions of the Cretaceous inland sea flooded most of Utah, the future Colorado Plateau, and nearly 2/3rds of North America leaving marine shales and sandstones such as the Mancos Shale, Dakota Sandstone and the Mesaverde Group.
LARAMIDE OROGENICS FINALIZE THE COLORADO PLATEAU'S LANDFORMS
East-directed Laramide compression was accommodated by folding that uplifted the plateau as a whole, and formed numerous northeast to northwest-trending broad anticlines and synclines. The Circle Cliffs Uplift is a classic example of the unique expression of Laramide deformation on the Colorado Plateau.
Both the San Rafael Swell to the north (See my post Part I) and the Circle Cliffs Uplift (better known as CapitolReefNational Park) are massive anticlinal upwarps that are bounded on their eastern margins by monoclines. Both of these colossal flexures trend generally to the northeast. The bedding in their flanks is Mesozoic, while deep canyons knife through the uplifts exposing strata as early as Permian in age. Not only have the forces of erosion dissected into the bowels of the uplifts within its canyons, but their anticlinal flexure has promoted characteristic erosion at their crests and at their monoclines. We both investigated and photographed these erosional features on our flight.
The monoclinal folds of these two uplifts, the San Rafael Reef and the Waterpocket Fold, respectively, drape over regional-scale reverse faults at depth in which the western block of basement rocks is thrust up and eastward over 7,000 feet relative to the down-dropped east side. The monoclines’ abrupt, single-limbs are the surface expression off the offset in the deep faults.
The sedimentary beds of a monocline such as Waterpocket Fold are deformed by a fault within the underlying bedrock. Characteristic erosional patterns are induced by the exposure of rock layers having varying resistance and susceptibility to attrition.
(Schematic from Essentials of Geology by Lutgens & Tarbuck, 2000)
EXTENSION CONVERTS TO COMPRESSION WHICH TRIGGERS REACTIVATION The monoclines drape over Laramide faults that had their genesis during the Late Precambrian during rifting along the western margin of Rodinia (proto-North America). Although initiated during a long period of extension, Laramide age reactivation was of intense compression, driven by a tectonic regime involving Farallon Plate subduction and two continuous orogenic events, the Sevier and Laramide Orogenies. The Late Cretaceous through early Tertiary Laramide phase created the Rocky Mountains and elevated the Colorado Plateau into existence as a distinct physiographic region. Thus, the movement along these long-lived, deep-cored, crustal-weaknesses is the opposite of the movement that they accommodated during their Precambrian birth.
This “reactivation” occurred all over the Colorado Plateau, forcing the Rockies to move vertically and the Plateau to rise en masse, creating it as a physiographic region. In so doing, the signature Laramide-derived uplifts, upwarps and swells with their associated monoclinal eastern flanks came into existence. As uplifts actively rose, basins actively subsided. The positive areas were attacked by erosion that generated vast quantities of sediment which were transported and deposited into the sinking basins.
FLYING FROM NORTH CAINEVILLE REEF TO THE LOWERCATHEDRALVALLEY
Our flight took us from the San Rafael Reef, the monocline of the San Rafael Swell, to the Caineville Reef, the southern extension of the monocline. The Caineville Reef essentially merges with the Waterpocket Fold to the south, the monocline of the Circle Cliffs Uplift.
That’s yours truly at the stick with Wayne Ranney nervously navigating.
THE PHOTO BELOW: NORTH CAINEVILLE REEF MONOCLINE
In this view we are flying almost due south over the North Caineville Reef, after having followed the strike of the San Rafael Reef. The southern extension of the reef beyond the mesa is aptly called the Southern Caineville Reef. The Waterpocket Fold is located to the south (at the center horizon) within CapitolReefNational Park. BoulderMountain is barely visible in the upper right corner. North Caineville Mesa is visible in the upper left. The black shadow is the plane’s right wheel partially obstructing the view.
Looking south along this stretch of the monocline where the upturned strata dips to the east at barely 30°, one really gets a sense of the tremendous volume of rock that has been lost by erosion. Off to the east (left), the rocks begin to flatten out and form plateaus and buttes such as North Caineville Mesa (artificially tilted by the angle of the plane on the left horizon). The mesa is capped by the MuleyCanyon (formerly Emery) Sandstone Member of the Mancos Shale, an older stratigraphic terminology used by Billingsley (Geologic Map of Capitol Reef, 1987). The badlands topography surrounding the mesa is formed by the Blue Gate Member of the Mancos Shale.
The landforms of the monocline, in typical fashion, are reflective of the resistance or susceptibility of the underlying bedrock to erosion. Strike valleys are generally formed on shale; whereas, sandstones, even from relatively thin units, stand up as ridges. The serpentine-shaped hogback ridge to the east is formed from the Ferron Sandstone Member of the Mancos Shale. Quaternary alluvial (stream and floodplain) deposits fill some sections of the strike valley (center photo) to the west, which is otherwise Tununk Shale of the Mancos. A subdued Dakota Sandstone ridge is followed by CedarMountain mudstones and sandstones. That's the varicolored Morrison Formation on the lower right.
THE PHOTO BELOW: CAINEVILLE REEF, CIRCLE CLIFFS UPLIFT AND BOULDER MOUNTAIN This spectacular view of the monocline is slightly south of the above view. The North Caineville Reef takes a big S-curve in this region, as we follow it to the southwest. In the distance the anticline of the Circle Cliffs Uplift is evident with Boulder Mountain framing the horizon with a dusting of late May snow. The buff-colored strata of Navajo Sandstone stand out as it plunges into the crust at the Waterpocket Fold. Desiring to approach the Waterpocket Fold from the west, we headed toward the Entrada red rocks of CathedralValley (right of center) in the northern portion of Capitol Reef.
THE PHOTO BELOW: CATHEDRAL VALLEY AND THOUSAND LAKE MOUNTAIN
CathedralValley is located in the northern portion of CapitolReefNational Park. The bedrock dips 3-5 degrees to the northeast. The topographic depression of CathedralValley is formed within the non-resistant, red-orange mudstone, siltstone and fine-grained sandstones of the Entrada Sandstone. The light gray caprock is Jurassic Curtis Formation. Red mudstone, siltstone and sandstone of the evenly-bedded Jurassic Summerville Formation overlies the Curtis. They are all Middle Jurassic sedimentary derivatives of the San Rafael Group, derived during a finger-like marine incursion that extended into the region from Wyoming. The Salt Wash Member of the Late Jurassic Morrison Formation overlies the Summerville the in the middle distance.
CathedralValley is known, in addition to other landforms, for its numerous free-standing monoliths, notably the Temple of the Sun and Moon. Over time, the towers become stranded by headward erosion, downcutting and slope retreat, and create the monoliths concurrent with the retreat of the valley walls. The formation of the monoliths is accelerated by erosion along fractures in the rock leaving unfractured, free-standing rocks, and preserved when resistant caps of Curtis rocks protect the underlying Entrada from erosion.
Late May snow has capped ThousandLakeMountain on the horizon, while in the middle distance is BlackMountain, both structures veneered with volcanics. CathedralValley is also known for its basalt dikes and sills, the composition of which matches that of the extruded basalt on top of ThousandLakeMountain (dated between 6.5 and 3.5 Ma). For reference, the monoliths of the Temple of the Sun and Moon are on the desert floor just beyond BlackMountain (in the middle distance), the sedimentary rocks of which are veneered with basalt.
THE PHOTO BELOW: THE MORRISON FORMATION
The colorful, banded, multi-membered Morrison Formation decorates the drab desert floor. Stratigraphically, the Tidwell Member of the Morrison laps onto the the underlying Middle Jurassic Summerville strata. Above that lies the Salt Wash Member distinguished by its whitish lenticular, cross-bedded channel sandstones. Next, the Brushy Basin Member is exposed as multi-colored claystones and bentonitic clays. The harder to distinguish fluvial-dominated, Cretaceous Cedar Mountain Formation lies above that (not seen in the photo). Both of these formations record the rise and eastward-push of the Sevier mountain-belt from the west.
ABOUT CAPITOLREEFNATIONAL PARK AND THE WATERPOCKET FOLD
Established in 1971, the nearly 242,000 acres of CapitolReefNational Park preserve and protect the rugged landscape of the Waterpocket Fold. The Fold is an immense northwest-trending monocline, a rugged spine almost 100 miles long from ThousandLakeMountain to the Colorado River in GlenCanyon (now submerged by LakePowell).
By definition, the monocline is comprised of flat-lying sedimentary rocks that drape over a deep fault on the eastern flank of the Circle Cliffs Uplift. The region is known for its stunningly colorful, craggy landscape and its variety of landforms such as mighty cliffs, slot canyons, natural bridges, arches, monoliths, hogback ridges and strike valleys. These erosional landforms were created by the exposure of rock layers of varying resistance and susceptibility to attrition. Typical of anticlines, older rocks are exposed in the core of the structure.
This is all beautifully depicted below in the stratigraphic profile that runs through the Circle Cliffs Uplift from Boulder Mountain on the west to the eastern edge of the monocline where it begins to flatten out. Notice in particular the unroofed Mesozoic rocks from the crest of the dome on the Teasdale Anticline and the canyon that has dissected to the Kaibab Formation. Also take note of the erosive patterns of the rock layers at the monocline that have formed upturned flatirons, strike valleys and hogback ridges.
(Modified from Ancient Landscapes of the Colorado Plateau by Ron Blakey and Wayne Ranney, 2008)
COMING TO TERMS
The term “capitol” was first used in reference to the dome-shaped outcrops of Navajo Sandstone in the vicinity of the FremontRiver that resemble the rotundas of capitol buildings. The nautical reference to a “reef” harkens back to the days of the pioneer’s with their covered wagons or prairie schooners. Upturned layers of resistant bedrock formed an unbroken barrier and an impediment to pioneers traveling to the west through the region. “Waterpockets” refer to circular depressions sculpted into flat sandstone surfaces that retain water. The cement around sand grains is dissolved and eventually removed by the wind. The pockets were an important source of water for early peoples that inhabited the region.
THE PHOTO BELOW: CIRCLE CLIFFS UPLIFT AND THE WATERPOCKET FOLD
Having just flown over CathedralValley and the surrounding Middle and SouthDeserts, we turned southwest over the Circle Cliffs Uplift. This photo looks to the south as we bank to the east toward the descending eastern limb of the uplift. The crest of the Circle Cliffs Uplift is in view with BoulderMountain in the distance and the slopes of ThousandLakeMountain encroaching from the right. The strata in the foreground are beginning their dip to the east in the direction of the Waterpocket Fold on the uplift’s eastern limb.
The town of Torrey, which is west of Capitol Reef and situated in the Moenkopi Formation (with a dip of 4° to the northwest being attributable to its location on the uplift’s western limb), lies between Boulder Mountain to its south and Thousand Lake Mountain to its north. The rocks on the Torrey-side of the Circle Cliffs Uplift were raised relative to its eastern limb at the monocline. The sedimentary rocks that comprise the region drape plastically with little deformation over the monocline at the Waterpocket Fold. Thus, the Moenkopi Formation, which lies at 7,000 feet in Torrey, dips down to the east and is at sea level beneath Caineville on Route 24 past the monocline. Interestingly, post-Laramide uplift during the Tertiary has contributed to additional rise of the Colorado Plateau, some of which is attributable to isostatic rebound in response to erosion.
THE PHOTO BELOW: THE DESCENDING EASTERN LIMB OF THE CIRCLE CLIFFS UPLIFT
Continuing our flight to the east toward the fold, this photo looks to the north. The MantiMountains of the Wasatch Plateau, which is west of the San Rafael Swell, are on the horizon. The Navajo Sandstone dips eastward with the plunging east limb of the monocline. Vertical joints in the Navajo are related to flexure of the descending limb.
THE PHOTO BELOW: CIRCLE CLIFFS UPLIFT, THOUSANDLAKEMOUNTAIN, WINGATE CLIFFS
Glancing back to the northwest, the massive anticlinal geometry of the Circle Cliffs Uplift is evident. Red Wingate Sandstone forms high plateaus and steep cliffs, as all the rocks gently dip to the west in the far left portion of the photo nearer to the uplift’s western limb. Wingate Sandstone is responsible for more miles of cliffs in Utah than any other formation, and is certainly evident here in the Capitol Reef region. Prominent fractures or joints are evident in the Wingate Sandstone in Circle Cliffs attributable to its flexure. In the foreground, the rocks dip to the right, toward the east, on the eastern limb of the uplift. Eventually, as we will see, the eastern limb plunges into the crust at the monocline.
Snow-capped ThousandLakeMountain graces the horizon. Lenses of buff-colored Navajo Sandstone can be seen on the right overlying the resistant Kayenta Formation. The Navajo-Kayenta-Wingate triad comprises the Glen Canyon Group. The slopes at the base of the cliffs are Triassic Chinle and Moenkopi formed in large river systems and broad, coastal floodplains, respectively.
Route 24 crosses CapitolReefNational Park from west to east and follows the escarpment of Wingate cliffs. The 30 mile ride from Torrey to Caineville on Route 24 takes in the Circle Cliffs Uplift and the monocline of the Waterpocket Fold. Beginning on the western limb of the Circle Cliffs Uplift, Route 24 travels in progressively younger rocks from the Lower Triassic Moenkopi Formation to the Upper Cretaceous Mancos Shale. The route proceeds upsection despite an elevation loss of over 2,100 feet, because the strata are tilted to the east. You can see this beautifully from the air!
THE PHOTO BELOW: THE GOOSENECKS OF SULFUR CREEK
Sulfur Creek flows from ThousandLakeMountain through the town of Torrey and meanders through an 800 foot deep canyon before emerging onto the upper flats above Fruita. Those meanders are called the “Goosenecks” of Sulfur Creek, seen in the photo. Sulfur Creek appears to show no regard for the uplift of Circle Cliffs which it defiantly cuts across. The explanation is that the creek’s serpentine nature was created before the uplift that elevated the region and folded the strata during the Paleocene and Eocene. The stream cut deeper into its channel to keep pace with the increase in elevation, and thereby created a gooseneck-landform. The “Goosenecks” are a classic example of a superimposed meandering river system.
The road to Gooseneck Overlook in the photo is reached off of Route 24. The overlook is perched on the Sinbad Limestone Member of the Moenkopi formation and peers into the deep canyon of Sulfur Creek. Immediately below, is a thin, red slope of Moenkopi shale, the Black Dragon Member. The Kaibab Limestone (or Black Box Dolomite) forms lower cliffs, while the eolian White Rim Sandstone (a member of the Cutler Group Undivided), the oldest rocks at Capitol Reef National Park, is at river level.
The western limb of the Waterpocket Fold monocline rolls over into the Teasdale Anticline. MinersMountain, beyond the Goosenecks, is the topographic expression of the Teasdale anticline, also held up by the Sinbad Limestone Member of the Moenkopi Formation. BoulderMountain is on the skyline to the left and ThousandLakeMountain to the far right with the town of Torrey nestled in between. BoulderMountain is the easternmost portion of the Aquarius Plateau. Both of these mountains are capped by Tertiary andesitic and basaltic lava flows with Boulder’s lavas dated between 30 and 20 Ma. Younger flows are also found on ThousandLakeMountain with a vent dated at 6.4 Ma. Interestingly, both mountains are on the High Plateaus, as is the Wasatch Plateau west of the San Rafael Swell (the “sister” uplift north of Circle Cliffs). The High Plateaus are the “transition zone” between the Basin and RangeProvince to the west and the Colorado Plateau to the east.
THE PHOTO BELOW: CAPITOLREEFVISITORCENTER, FRUITA AND THE CASTLE
We continued our flight path to the east toward the monocline along Route 24. The red-roofed VisitorCenter can be seen with a portion Fruita’s verdant orchards. Also note the solitary, towering Castle against a backdrop of Wingate cliffs. Sulfur Creek can be spotted winding through the flats along with Route 24 after having emerged from the Goosenecks.
“The Castle” is formed of eolian Early Jurassic Wingate Sandstone, as are the massive cliffs behind it. Much of the escarpment-face can be seen to be fluted by vertical jointing in the Wingate. Below the escarpment, mudstones and siltstones of the underlying Chinle Formation undercut the Wingate’s vertical cliffs. Three members of the Chinle are visible here: the uppermost, pastel-colored Owl Rock Formation partly obstructed by Wingate talus, the ledge-slope of the variegated Petrified Forest Member, and the lowest slope of the greenish-gray Monitor Butte Member. The dark-colored rocks at the base are the Early Triassic Moenkopi Formation. The high alkaline content of the Moenkopi inhibits plant growth. There is no basal Shinarump Conglomerate Member separating the two slope-forming formations in this region.
THE PHOTO BELOW: FRUITA, THE CONFLUENCE OF SULFUR CREEK AND THE FREMONTRIVER, JOHNSON
Still following Route 24 to the east, we’re looking back at the red-roofed VisitorCenter just beyond the orchards on the edge of Fruita. The confluence of Sulfur Creek and the FremontRiver is at the foot of Johnson Mesa. Fremont pictographic panels are found along the foot of the Wingate cliffs in this section of the FremontRiver and below. Desert varnished Wingate cliffs are topped by the vegetated Kayenta Formation. The green of Fruita created a beautiful contrast against the region’s red rocks.
The Historic District of Fruita, a Mormon homestead established in 1880 with its lush orchards of more than 2,700 fruit trees containing peaches, pears, cherries and apples, has few remaining original buildings and is under the auspices of the National Park Service. The well-attended, living orchards aptly preserve the legacy of the early settlers. Fruita sits at the confluence of the FremontRiver and Sulfur Creek and lies at the contact of the Moenkopi and Chinle Formations which has created the relatively flat area around the town. The Chinle’s basal Shinarump Conglomerate Member is conspicuously absent in this region.
Note prominent Johnson Mesa centered between the confluence. It is a strath terrace, which is a terrace cut into bedrock as a river (the Fremont) expanded its floodplains, and then was abandoned as streams cut deeper channels. Johnson Mesa is a remnant of a debris flow that originated on BoulderMountain and is littered with large, coarse basaltic-andesitic boulder deposits with exposure ages of ~190,000 years ago. These characteristic black boulders are to be found throughout the FremontRiverValley. Here in Capitol Reef, it appears that terrace formation and later incision were in response to periods of glacial growth and decline.
The hypothesized dynamics are follows: Terraces associated with Sulfur Creek record the central pathway of ancient streams rather than the lateral extent of the floodplain. Volcanic boulder-rich terrace deposits were liekly created as stream channels were clogged with volcanic boulders and subsequently abandoned. The boulder-fill effectively armored the underlying softer bedrock. As the stream moved away from the abandoned, boulder-filled channel, it eroded and downcut into the adjacent, softer, mudstone bedrock, rather than eroding through the more resistant boulder alluvium. Thus, the abandoned boulder-filled channel became elevated relative to the stream. This inverted topography is preserved as elevated, fluvial terrace-deposits. This style of preservation of linear terraces developed over a broad area is in contrast to nearby terraces along the Fremont River which are preserved as "steps" cut into the resistant sandstones of the Glen Canyon Group along the Waterpocket Fold. These terraces have been used to identify changes in the location of Sulfur Creek through time (Samuel Sorber, Master Thesis, 2006, BYU).
THE PHOTO BELOW: ROUTE 24, FREMONTRIVER, NAVAJO DOMES
We’re flying to the southeast across the eastern flank of the monocline which can be seen dipping to the right. The photo looks to the northeast with the FremontRiver and Route 24 below. The town of Fruita is immediately behind us out of view. Route 24 continues to the monocline and crosses the strike valleys of the fold from west to east and was known as the Blue Dugway during its pioneer days due to the distinctive color of the Mancos shales.
On the horizon to the right of center, we can make out Factory Butte and North Caineville Mesa (see my Post I) lying along the Caineville Reef, north of the Waterpocket Fold. On the horizon (to the left) we can barely discern the dome of the San Rafael Swell in the haze.
There are several Fremont petroglyphic panels along this stretch of 24 carved into the lowermost parts of the Wingate Sandstone just above the Chinle contact. The prehistoric Fremont Culture existed throughout Utah and adjacent areas of Idaho, Colorado and Nevada from approximately AD 600 - 1300. Fremont culture is primarily defined by a consistent set of traditions and practices that have been identified as unique and separate from their contemporaries, the Ancestral Puebloans.
Note the characteristic, eroded Navajo domes and the dip of the strata to the east (left). Large scale cross-bedding in the sandstone is evident even from this aerial perspective. Our flight to the east is heading straight for the Waterpocket Fold monocline.
THE PHOTO BELOW: THE ENIGMATIC BLACK BOULDERS OF CAPITOL REEF
About 25 to 20 million years ago, volcanoes extruded andesitic and basaltic lava that flowed over the eroded and folded strata of the Waterpocket fold. The transportation of the large, angular boulders downslope was presumably a combination of debris flows, flash floods, alluvial, and possibly glacial processes tens of miles across broad valley floors. The Fremont and EscalanteRivers have since cut deeply into those floors, carving canyons and erosion that re-exposed the resistant bedrock. The old valley floors are now mesas (or strath terraces) that are up to 600 feet above the present river valleys. That left the enigmatic boulders stranded on the high terraces. River processes rounded some of the boulders, many of which are perched and strewn on the bedrock of mesas and terraces above the modern valley floor. The remnants of these flows still cap the High Plateaus of nearby Boulder and ThousandLakeMountains west of Capitol Reef. Recent dating has yielded ages for the boulders of 60,000, 100,000 and 150,000 years that correspond to times of glacial maxima, except for the recent interval that ended 12,000 years ago.
THE PHOTO BELOW: CLIFFS AND DOMES OF NAVAJO SANDSTONE
Still flying to the east toward the monocline with the strata dipping to the left, more eroded and checker-board fractured Navajo Sandstone domes come into view. This view looks southward. BoulderMountain is to the southwest. The rounded namesake-domes of Capitol Reef were created by a combination of headward erosion, downcutting, slope retreat and weathering of the cross-bedded Navajo Sandstone.
THE PHOTO BELOW: NOTOM, BROADSTRIKEVALLEYS AND THE HENRYS
We’re looking down over the farm and ranchland at Notom situated on a Pleistocene debris flow terrace situated within a Mancos strike valley. According to oral tradition, Notom means “no town” which seemed to be fairly accurate.
We have exited the plunging monocline’s eastern limb and the terrain has become flat, punctuated with numerous long ridges that follow the strike of the fold. These erosional features are in direct response to the exposure of erodable and resistant rock layers.
In the distance, the snow-capped HenryMountains were in clear view. The Henrys were formed over shallow igneous intrusions consisting largely of plagioclase-hornblende porphyry emplaced 31.2 to 23.3 Ma and that domed the overlying sedimentary rock. They consist of five main peaks with Mount Ellen being the northernmost and tallest at 11,615 feet. John Wesley Powell named the Henrys after Joseph Henry of the Smithsonian Institution who supported his Colorado River exploration. They were the last mountain range in the continental United States to be mapped and explored.
THE PHOTO BELOW: THE WATERPOCKET FOLD MONOCLINE
Now directly over the strike valley of the Waterpocket Fold, we banked to the south to follow in its strike. The signature landform of the monocline is very evident with its broad strike valleys punctuated by resistant hogback ridges. Recall that uplift was accompanied by erosion. That attacked the rocks at the crest of the anticlinal uplift and at the monocline, sculpting the various rock layers that have become exposed. Some rock layers being resistant to erosion have resulted in the formation of prominent hogback ridges, flatirons, while susceptible layers have formed smooth strike valleys.
A faint profile of the laccolithic dome of Navajo Mountain can be made on the horizon to the right of center, a distance of about 65 miles. A small section of Tarantula Mesa appears on the farthest left (east) composed of Cretaceous Tarantula Mesa Sandstone (informally known as the Mesaverde Formation) sandstones and shales. Tarantula Mesa lies in the HenryMountainsBasin. Cretaceous seaway deposits of the Mancos Formation occupy the two strike valleys, the Masuk Member on the east and the Blue Gate Member on the west separated by the prominent upturned-hogback ridge made of the Muley Canyon Member (formerly the Emery Sandstone Member). The plunging nature of the monocline is evident as chevrons of Carmel Formation lie on massive buff-colored Navajo Sandstone as they project skyward at almost 45°.
THE PHOTO BELOW: UPTURNED CHEVRONS AND FLATIRONS ON DISPLAY AT THE FOLD
Flying south along the strike of the Waterpocket Fold, we are facing the monocline’s plunging eastern limb head on. The dips of the sedimentary rocks range from 14° to more than 50° to the east. The red cliffs of the Early Jurassic Glen Canyon Group’s Wingate Sandstone are not visualized from this view of the monocline, but we’ve seen its cliffs throughout the crest and limbs of the uplift to the west. The ledgy, vegetated Kayenta Formation can be seen at the summit of the monocline overlain by the massive white Navajo Formation. Recall that the cross-bedded Navajo was deposited in an enormous sand dune-filed or erg and is about 1,000 feet thick in this region.
The Middle Jurassic San Rafael Group is also on display. Its brick red Summerville Formation caps the greenish-gray sandstones of the Curtis Formation which overlie the redbeds of the Entrada Sandstone, non-eolian in this western region. Hence, the traditionally more resistant Entrada wears more readily unless capped by the more resistant Curtis Formation (such as in CathedralValley). Recall that the group represents several marine incursions and retreats of seas from the north that extended through central Utah. All the softer layers contribute to the formation of a strike valley. The Summerville is capped by the erodable Tidwell Member of the Morrison Formation. Looking to the east of the angular strike of the monocline, the Morrison’s Members alternately form narrow ridges with the resistant Salt Wash Member’s resistant sandstones and small strike valleys with the Brushy Basin Member’s soft bentonitic claystones. The overlying Cedar Mountain Formation is difficult to decipher from the air (and even on the ground) with its fewer colors and less defined color bands.
Eroded multi-colored, saw-teeth chevrons of Entrada Sandstone and Carmel Formation abut the massive, tilted strata of the Navajo Sandstone, as it all appears to plunge into (or emerge from) the crust. Beyond the Navajo is reddish Kayenta Formation at the crest. Uplift is accompanied by erosion that stripped thousands of feet of Late Paleozoic and Mesozoic strata from the region and created the spectrum of desert landforms for which Capitol Reef is famous.
THE PHOTO BELOW: MANCOS HOGBACK RIDGES AND STRIKEVALLEYS
Looking directly below us to the east across a flat expanse of Mancos Shale, a sharp ridge of Muley Canyon Member separates upper badlands of younger Masuk Member from the pock-marked Blue Gate Shale Member of the Mancos strike valley below.
THE PHOTO BELOW: THE WATERPOCKET FOLD LOOKING SOUTH
This photo is taken off the nose and through the spinning propeller of our Cessna. It looks to the south at the Waterpocket Fold about 25 miles south of Route 24. We get a spectacular, big picture-view of the Waterpocket Fold as it dives into the crust at the monocline. Note the differential erosion that has created various resistant hogback ridges, erodable strike valleys, and upturned flatirons characteristic of the fold. The resistant strata can be seen to be sharply upturned toward the crest of the anticline to the right (west) with the youngest formations to the east. The Notom-Bullfrog Road that runs in a strike valley parallel to the generally north-south strike of the fold from the small agricultural settlement of Notom in the north to Bullfrog at Lake Powell in the south.
The Mancos Shale is truly on display with five members readily recognizable. It is the thickest unit in Capitol Reef with a total thickness of more than 3,000 feet. The Mancos records the repeated advances and retreats of the western shoreline of the Western Interior Seaway during the Cretaceous Period. Simply stated, the resistant sandstone members (recording advances of the Western Interior Seaway) are Ferron and MuleyCanyon, and the softer shale units are Tununk, Blue Gate and Masuk.
Stratigraphic interpretation of the above photo:
The Mesaverde Formation (Kmv) forms the prominent escarpment of Tarantula Mesa to the far left (east). The mesa continues to the east into the HenryMountainBasin. Extending below the escarpment is a badlands region (to the west) comprised of the mudstones of Masuk Member (Kmm) Mancos Shale. Sandstones of the Muley Canyon Member (Kmmc) of the Mancos Shale are sharply upturned above a wide strike valley of Blue Gate Member (Kmbg) shale of the Mancos. The Ferron Sandstone (Kmf) Member of the Mancos forms a thin ridge (at the center of the photo) above a strike valley of Tununk Member (Kmt) shales of the Mancos. The Dakota Sandstone (Kd) forms a variable ridge (with an upper fossiliferous unit known as Oyster Shell Reef and a lower unit with coal prospects). The Dakota variably stands above a strike valley of Cedar Mountain (Kcm) mudstone and sandstone, and Brushy Basin Member (Jmbb) shale of the Morrison Formation, deposited in response to tectonic uplift to the east. The Notom-Bullfrog Road occupies the narrow strike valley in this stretch of the fold. Rather subdued in this section of the fold but more prominent to the north, Salt Wash Member sandstones (Jmsw) of the Morrison Formation form a small hogback ridge. The San Rafael Group’s Summerville Formation siltstones and mudstones (Js), Curtis Formation sandstones (Je), and Entrada marine sandstones and siltstones (Je), unlike more massive eolian sandstones in Canyonlands to the east, form slope-forming sections. Sharply upturned strata of Carmel Formation (Jc) sandstones and siltstones form triangular-shaped flatirons that overlie massive exposures of the Glen Canyon Group’s Navajo Sandstone (Jn). Far to the right in the photo, Kayenta sandstones and siltstones (Jk) project upward toward the crest of the anticline. Off the photo to the right, the Wingate Sandstone forms high, jagged cliffs.
THE PHOTO BELOW: THE SWITCHBACKS OF THE BURR TRAIL
The Burr Trail probably has a history very much like other old roads in Utah starting out as a Native American travel route. In the 1880’s, the Burr Trail was used by John Atlantic Burr and others to move cattle from the Aquarius Plateau on Boulder Mountain to Bullfrog Basin near the Colorado River in Arizona. The trail was later used for its access to mineral resources especially uranium during the 1950’s. Today, the Burr Trail provides a scenic link between the town of Boulder, CapitolReefNational Park and Glen Canyon National Recreation Area to the south.
Its six-switchbacks in the slope of the Kayenta Formation are accessed by a wide erosive gap in the Entrada and Carmel, and an unusually wide break in the Navajo Sandstone. The gap allowed the trailto climb the flank of the otherwise impassable monocline. All three formations of the Glen Canyon Group are on display here with strata dipping about 35° to the east: massive white Navajo sandstone cliffs, the red ledgy Kayenta Formation, and massive red cliffs of Wingate Sandstone.
THE PHOTO BELOW: SOUTHERN SECTION OF THE WATERPOCKET FOLD
Looking southwest from the flats below Swap Mesa in the Ferron Sandstone Member, this view takes in the southern section of the Waterpocket Fold. From this oblique angle we get a perfect perspective of the eastern limb of Circle Cliffs Uplift as it plunges into the crust at the monocline. The Navajo Sandstone stands out as it is reflected to the east, somewhat subdued in its angulation from further north in the monocline. Lying below it, the heavily vegetated Kayenta formation rises to a large plateau held up by Wingate Sandstone.
The 1875 sketch below of the "Waterpocket Canon and the Waterpocket Flexure" was made by G.K. Gilbert, a geologist assigned by John Wesley Powell to map and study the Henry Mountains to the east.
(Obtained from Geology of the Henry Mountains by G.K. Gilbert, USGS of the Rocky Mountains, 1880)
Our plane banked to the southeast away from the Waterpocket Fold in order to fly around the Henry Mountains, the southern turnaround point of our flight and the subject of my future post entitled “Flight Plan: Part III – Geology of the Henry Mountains Laccolith.” The Waterpocket Fold continues to Lake Powell, another 15 miles or so.