National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Glen Canyon National Recreation Area

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1264
ON THE COVER: Horseshoe Bend entrenched meander, Colorado River, Glen Canyon National Recreation Area.

National Park Service photograph.

THIS PAGE: Slickrock sandstone cliff with desert varnish and cross-bedding.

National Park Service photograph by Bob Moffit.
Glen Canyon National Recreation Area

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1264

John P. Graham

Colorado State University Research Associate

National Park Service Geologic Resources Division

Geologic Resources Inventory

PO Box 25287

Denver, CO 80225

August 2016

U.S. Department of the Interior

National Park Service

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado, publishes a 

range of reports that address natural resource topics. These reports are of interest and applicability to a broad audience 

in the National Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate comprehensive information and analysis about natural 

resources and related topics concerning lands managed by the National Park Service. The series supports the 

advancement of science, informed decision-making, and the achievement of the National Park Service mission. The 

series also provides a forum for presenting more lengthy results that may not be accepted by publications with page 

limitations.

All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically 

credible, technically accurate, appropriately written for the intended audience, and designed and published in a 

professional manner. This report received informal peer review by subject-matter experts who were not directly 

involved in the collection, analysis, or reporting of the data.

Views, statements, findings, conclusions, recommendations, and data in this report do not necessarily reflect views and 

policies of the National Park Service, U.S. Department of the Interior. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use by the U.S. Government. 

This report is available from the Geologic Resources Inventory website (http://go.nps.gov/gripubs), and the Natural 

Resource Publications Management website (http://www.nature.nps.gov/publications/nrpm/). To receive this report in 

a format optimized for screen readers, please email irma@nps.gov.

Please cite this publication as:

Graham, J. P. 2016. Glen Canyon National Recreation Area: Geologic Resources Inventory report. Natural Resource 

Report NPS/NRSS/GRD/NRR—2016/1264. National Park Service, Fort Collins, Colorado.

NPS 608/133731, August 2016
iii

Contents

Page

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix

Products and Acknowledgments . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

GRI Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Geologic Setting and Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Geologic Heritage .

Park Significance and Fundamental Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Geologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Geologic Significance and Connections .

Geologic Features and Processes . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Landscape Features .

Sedimentary Rocks and Sedimentary Rock Features .

Unusual Sedimentary Rock Features .

Paleontological Resource .

Caves and Karst .

Paleosols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Unconformities .

Folds and Faults .

Joints .

Laccoliths .

Unconsolidated Surficial Deposits .

Hite Delta Geomorphic Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Economic Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Geologic Type Sections .

Geologic Resource Management Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

Landscape Safety Hazards .

Slope Movement Hazards and Risk .

Flash Floods and Debris Flows .

Paleontological Resource Inventory, Monitoring, and Protection .

Cave and Alcove Management .

Sediment Deposition in Lake Powell .

Abandoned Mineral Lands and Potential Mining Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

Potential Impacts from Global Climate Change .

Earthquakes. .

Glen Canyon Dam and Downstream Impacts to the Colorado River .

Navajo Sandstone and Potential Glen Canyon Dam Failure .

Geologic History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

Pennsylvanian and Permian Periods: Shallow Seas and Assembling Pangea .

Triassic Period: Fluvial Systems in a Tropical Climate .

Jurassic Period: Extensive Dune Fields .

Cretaceous Period: Western Interior Seaway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

Cretaceous–Paleogene Periods: The Laramide Orogeny .

Paleogene Period (Oligocene Epoch): Laccolith Emplacement .

Paleogene–Quaternary Periods: Colorado River System and Carving Glen Canyon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Glen Canyon National Recreation Area And Other NPS Areas Along The Colorado River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
iv

Contents (continued)

Page

Geologic Map Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Geologic Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Source Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

GRI GIS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

GRI Posters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Map Unit Properties Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Use Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

Additional References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

Geology of National Park Service Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

NPS Resource Management Guidance and Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Climate Change Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Geological Surveys and Other Organizations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

US Geological Survey Reference Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .117

Appendix A: Scoping Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119

1999 Scoping Meeting Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

2015 Conference Call Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .119

Appendix B: Geologic Resource Laws, Regulations, and Policies . . . . . . . . . . . . . . . . . . . . . . . . . 121

GRI Posters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket

Map Unit Properties Tables . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket
v

Figure 1. Physiographic provinces of the western United States.

Figure 2. Photograph of Reflection Canyon in Lake Powell, Glen Canyon National Recreation Area.                                               .

Figure 3. Geologic time scale.

Figure 4. Stratigraphic column for Glen Canyon Recreation Area and vicinity.

Figure 5. Exaggerated geologic cross-sections for Glen Canyon National Recreation Area 

Figure 6. Historic photograph of ferryboat at Lees Ferry.                                                                                           .

Figure 7. Photograph of buttes, alcoves, and outcrop patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 8. Photograph of slickrock in Glen Canyon National Recreation Area.                                                                     . 

Figure 9. Photograph of Navajo Sandstone alcove with a hanging garden in Knowles Canyon, Glen Canyon National Recreation Area .

Figure 10. Photograph of Broken Bow arch, Glen Canyon National Recreation Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 11. Photograph of Rainbow Bridge, Rainbow Bridge National Monument.

Figure 12. Photograph of Horseshoe Bend, Glen Canyon National Recreation Area. 

Figure 13. Photographs of fluidized injections of sandstone into Entrada Sandstone and a weathering pit that formed on a sandstone pipe.

Figure 14. Schematic illustrating the Interfingering of the Elephant Canyon and the Halgaito Formations 

Figure 15. Photograph of cross-section of mudcracks, Red Canyon, Glen Canyon National Recreation Area  

Figure 16. Schematic cross-section of a sand dune . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 17. Photograph of cross-bedding in Jurassic Navajo Sandstone sand dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 18. Photographs of features typically found in the “oasis” deposits in the Navajo Sandstone . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 19. Unusual sedimentary features in the Navajo and Entrada sandstones, Glen Canyon National Recreation Area.

Figure 20. Photograph of dinosaur tracks in the Powell Fossil Track Block tracksite, Glen Canyon National Recreation Area.                     . 

Figure 21. Photograph of Bechan Cave, Glen Canyon National Recreation Area. The alcove formed in Navajo Sandstone

Figure 22. Photograph of paleosols in the Chinle Formation, between Twomile and Fourmile Canyons, Glen Canyon National Recreation Area 

Figure 23. Schematic diagram across the Circle Cliffs anticline, which trends north–south to northwest–southeast through Glen Canyon National

Recreation Area .

Figure 24. Schematic illustrations of fault types.

Figure 25. Photograph of Navajo Mountain.                                                                                                     . 

Figure 26. Photograph of clasts of river alluvium south of Antelope Island.

Figure 27. Photograph of river-cut terrace near Oak Canyon, Glen Canyon National Recreation Area.                                           . 

Figure 28. Photograph of landslide scarp along the east shore of Good Hope Bay, Glen Canyon National Recreation Area.

Figure 29. Photograph of cliff along the west shore between Twomile and Fourmile Canyons, Glen Canyon National Recreation Area 

Figure 30. Photograph of a mud volcano on the Hite delta, Glen Canyon National Recreation Area 

Figure 31. Photograph of a collapsed mud volcano on the Hite delta, Glen Canyon National Recreation Area 

Figure 32. Map showing the location of the Tar Sand Triangle and road access.

Figure 33. Schematic geologic cross-section through the Tar Sand Triangle 

Figure 34. Photograph of the Page Sandstone at its type locality on Manson Mesa, Arizona.

Figure 35. Photograph of visitors overlooking the popular Horseshoe Bend, Glen Canyon National Recreation Area . . . . . . . . . . . . . . . 6

Figure 36. Photograph of moqui marbles 

Figure 37. Photograph of a cloud of dust from a rockfall 

Figure 38. Photograph of boulders and mud covering the road to Lees Ferry following the September 2013 flood 

Figure 39. Map of Slick George Dinosaur Tracksite, Glen Canyon National Recreation Area 

Figure 40. Photographs of mitigation work at the Jomac Mine, Glen Canyon National Recreation Area 

Figure 41. Map of earthquake probability for Glen Canyon National Recreation Area 

Figure 42. Middle Pennsylvanian (308 million years ago) and Early Permian (280 million years ago) paleogeographic maps of North America 

Figure 43. Mesozoic Era paleogeographic maps of North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figures

Page

vii

Tables

Page

Table 1. Summary of unconsolidated deposits mapped in Glen Canyon National Recreation Area 

Table 2. American Indian history in Glen Canyon National Recreation Area 

Table 3. Landscape features in Glen Canyon National Recreation Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Table 3. Landscape features in Glen Canyon National Recreation Area, continued 

Table 4. Sedimentary rock classification and characteristics 

Table 5. Sedimentary rock features identified in Glen Canyon National Recreation Area 

Table 6. Relative distribution of tracks and bones found in the stratigraphic units along the shoreline of Lake Powell, Glen Canyon National

Recreation Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Table 7. Paleozoic Era fossils found in Glen Canyon National Recreation Area or its immediate vicinity . . . . . . . . . . . . . . . . . . . . . . 3

Table 8. Mesozoic Era fossils found in Glen Canyon National Recreation Area 

Table 8. Mesozoic Era fossils found in Glen Canyon National Recreation Area, continued.                                                       . 

Table 9. Quaternary Period fossils found in Glen Canyon National Recreation Area.

Table 10. Designated and unofficial type sections for formations within or in the vicinity of Glen Canyon National Recreation Area 

Table 11. Geology data layers in the Glen Canyon National Recreation Area GRI GIS data 

ix

Executive Summary

The Geologic Resources Inventory (GRI) is one of 12 inventories funded by the National Park Service 

(NPS) Inventory and Monitoring Program. The Geologic Resources Division of the NPS Natural 

Resource Stewardship and Science Directorate administers the GRI. This report synthesizes discussions 

from a scoping meeting for Glen Canyon National Recreation Area (Arizona and Utah) on 23–25 

September 1999 and a follow-up conference call on 5 March 2015, which were held by the Geologic 

Resources Division to determine geologic resources, the status of geologic mapping, and geologic 

resource management issues and needs. It is a companion document to previously completed GRI GIS 

data.

Glen Canyon National Recreation Area encompasses 

geologic features, landforms, and landscapes that 

are part of America’s geologic heritage. Preservation 

of these features enriches a full range of values that 

contributed, and continue to contribute, to our 

country’s history and culture. Glen Canyon National 

Recreation Area was established in 1972 to preserve 

the area’s scenic, scientific, and historic features and to 

provide public use and enjoyment of Lake Powell. The 

recreation area’s 506,000 ha (1.25 million ac) not only 

include Lake Powell but also sections of the Colorado 

and San Juan rivers. About 51% of Glen Canyon 

National Recreation Area consists of proposed and 

potential wilderness, considered to be a fundamental 

resource in the recreation area’s Foundation Document.

Located on the Colorado Plateau, a physiographic 

province that spans roughly 34 million ha (84 million 

ac), Glen Canyon National Recreation Area shares a 

border with other national park system units including 

Grand Canyon National Park, Capitol Reef National 

Park, Canyonlands National Park, and Rainbow Bridge 

National Monument. In addition, the recreation area 

shares 800 km (500 mi) of its southern boundary 

with the Navajo Nation, and it adjoins public lands 

administered by the Bureau of Land Management, 

including the Grand Staircase-Escalante and Vermilion 

Cliffs National Monuments and the Paria CanyonVermilion cliffs Wilderness. 

Lake Powell began filling behind Glen Canyon 

Dam in 1963. At full capacity, Lake Powell is 299 km 

(186 mi) long and contains 3,150 km (1,960 mi) of 

shoreline, which includes 96 major side canyons. The 

spectacular landscape includes over 3,000 m (10,000 

ft) of sedimentary rocks that represent approximately 

300 million years of Earth history. This geologic history 

includes several mountain–building events (orogenies), 

the formation of the supercontinent Pangea, multiple 

incursions of shallow seas onto the North American 

continent, vast deserts with Sahara-like sand dunes 

(ergs), the rise and demise of the dinosaurs, unique 

igneous intrusions known as laccoliths, and the carving 

of the Colorado River system. The recreation area has 

one of the most extensive exposures of Mesozoic Era 

rocks of any National Park Service unit, providing 

exceptional documentation of ecosystems and 

paleoclimates from approximately 252 million to 66 

million years ago.

This dynamic history is expressed in the recreation 

area’s myriad geologic features and associated 

processes, which include: 

● Landscape Features. Mesas, buttes, cliffs, 

slickrock, slot canyons, alcoves, hanging gardens, 

arches, natural bridges, badlands, hoodoos, 

entrenched meanders, desert varnish, sandstone 

pipes, and weathering pits are just some of the 

features that record the processes that shaped the 

Glen Canyon National Recreation Area landscape. 

● Sedimentary Rocks and Sedimentary Rock 

Features. The bedrock in Glen Canyon National 

Recreation Area consists of sedimentary rock, 

one of the three basic rock types. Features in 

the sedimentary rock strata document marine, 

nearshore marine, fluvial, and eolian environments 

that have transformed the landscape of 

southeastern Utah through geologic time.

● Unusual Sedimentary Rock Features. Oasis 

deposits, Moqui (Moki) marbles, soft sediment 

deformation, and tafoni record unusual 

environments and processes preserved in the 

sedimentary rock strata.

● Paleontological Resources. Marine fossils are 

common in Paleozoic limestones, while dinosaur 
x

tracks are found in the terrestrial Mesozoic units. 

Pollen extracted from dung and packrat middens 

have provided evidence for the ecology and climate 

during the more recent Quaternary Period. Cultural 

sites contain artifacts fashioned from rocks and 

fossils, such as projectile points and scrapers 

fashioned from petrified wood.

● Caves and Karst. Numerous alcoves and caves 

have formed in the Navajo Sandstone and Cedar 

Mesa Sandstone cliffs. One of the more significant 

caves is Bechan (“big feces” in Navajo) Cave. 

The single-room cave, or alcove, contains 300 m3

(10,600 ft3) of fossil sloth and mammoth dung. 

Dung, hair, teeth, and bones found in Bechan Cave 

date back thousands of years. Paleozoic carbonate 

strata provide potential sites for solution caves, 

which are a characteristic of karst topography.

● Paleosols. These ancient soils, especially those 

found in the Chinle Formation, provide clues to 

past climates. 

● Unconformities. Significant regional 

unconformities document millions of years of 

erosion or non-deposition during the Mesozoic 

Era.

● Folds and Faults. Faults, some reactivated 

throughout geologic time, and broad, asymmetrical, 

north- to northwest-trending folds, such as the 

regional Circle Cliffs anticline, resulted from 

tectonic events that deformed the Colorado 

Plateau.

● Joints. Near-vertical, inclined, and surficial joints 

fracture the bedrock in Glen Canyon National 

Recreation Area. The joints are partly responsible 

for the formation of slot canyons, rockfalls, and 

natural arches.

● Laccoliths. These mushroom-shaped igneous 

intrusions resulted from magma being forcefully 

injected along bedding planes, causing overlying 

strata to dome-upward. They form the domeshaped Henry Mountains and Navajo Mountain, 

which are within the viewshed of Glen Canyon 

National Recreation Area.

● Unconsolidated Surficial Deposits. Surficial 

deposits in Glen Canyon National Recreation Area 

fall into seven categories: (1) alluvium, (2) eolian, 

(3) mass-wasting, (4) colluvium, (5) residuum,

(6) lacustrine, and (7) tufa deposits. Each of these 

deposits represents specific processes that have 

been operating throughout geologic time.

● Hite Delta Geomorphic Features. The drought 

of 2000–2005 exposed domes, mud volcanoes, 

pockmarks, polygonal joints, slumps, and lateral 

spreads on the Hite delta. Analyses of these features 

may allow researchers to distinguish between 

seismic (earthquake) and non-seismic triggering 

mechanisms.

● Economic Minerals. Bitumen in the form of 

tar sands, gold, uranium, and coal occur in the 

recreation area. Tar sand deposits in the White Rim 

Sandstone intersect the northern portion of the 

recreation area. Gold dust, originating from the 

mountains of Colorado, mixes with river gravels in 

the recreation area. Uranium occurs in sandstones 

and conglomerates of Jurassic and Triassic strata. 

Coal beds are present in Cretaceous strata.

● Geologic type sections. Eleven of the mapped 

units have designated type sections (locations 

where a unit was first described) or other reference 

sections within or adjacent to Glen Canyon 

National Recreation Area.

Geologic resource management issues identified 

during the GRI scoping meeting in 1999 and follow-up 

conference call in 2015 include the following:

● Landscape Safety Hazards. Overlooks offer 

impressive views of the landscape, but they also 

present a potential hazard for visitors. Fatalities 

from falls have occurred at overlooks and along 

slick trails.

● Slope Movement Hazards and Risk. Landslides, 

slumps, slides, and rockfalls are common in the 

recreation area and can adversely impact park 

resources, infrastructure, and/or visitor safely. 

Erosion of less-resistant slopes, especially in the 

Chinle Formation, may undercut cliffs and lead to 

cliff collapse.

● Flash Floods and Debris Flows. Intense 

thunderstorms and sparse vegetation result in rapid 

runoff and flash floods through the narrow canyons 

in the recreation area. Debris carried by these 

floods may damage or destroy park infrastructure, 

as well as threaten visitor safety.

● Paleontological Resource Inventory, Monitoring, 

and Protection. In 2009, Glen Canyon National 

Recreation Area was selected as the prototype 

paleontological resource monitoring park for the 

National Park Service. The park maintains an 

inventory and monitoring database for the fossil 
xi

sites in the park. Natural degradation and fossil 

theft remain a concern for resource managers.

● Cave and Alcove Management. The caves and 

alcoves in Glen Canyon National Recreation Area 

contain a diverse assemblage of paleontological 

and cultural resources. A park-specific cave/alcove 

management plan should provide a comprehensive 

evaluation of current and potential visitor use and 

activities, as well as a plan to study known and 

discover new caves. 

● Sediment Deposition in Lake Powell. Because 

of Glen Canyon Dam, sediment is continuously 

deposited in Lake Powell. Sediment deposition 

has impacted several locations in the lake, 

including paleontological sites. Climate change 

models predict lower lake levels due to higher 

temperatures, decreased precipitation, and 

decreased runoff. As lake levels lower and 

sedimentation continues, storage in Lake Powell 

will be reduced. 

● Abandoned Mineral Lands and Potential Mining 

Activity. Abandoned mineral lands in Glen Canyon 

National Recreation Area include mine adits, waste 

rock, abandoned oil and gas wells, surface mines, 

abandoned mining equipment, buildings, and 

roads. External and internal mining activities that 

may require remediation or impact the recreation 

area include past uranium mining, coal mining, 

burning coal beds in neighboring Grand StaircaseEscalante National Monument, external oil and gas 

exploration, and current tar sands exploration and 

development.

● Potential Impacts from Global Climate Change. 

A decline in winter precipitation may adversely 

impact the aquifers, springs, and seeps upon which 

the fragile ecosystems of the hanging gardens 

depend. A decline in precipitation may also lower 

the water level in Lake Powell, adversely impacting 

visitor access and increasing rockfall potential along 

the shoreline.

● Earthquakes. The probability of an earthquake 

with a magnitude >5 shaking the recreation area in 

the next 100 years is 0.04 to 0.30. The southern part 

of the recreation area, where Glen Canyon Dam 

was built, has a greater chance of an earthquake 

than the northern section.

● Glen Canyon Dam and Downstream Impacts 

to the Colorado River. With the closure of Glen 

Canyon Dam, average peak flows decreased and 

the downstream Colorado River channel narrowed 

and became dominated by cobbles and rocks. In 

the 1960s, flushing discharges scoured most of the 

sand out of the channel. Nonnative vegetation now 

stabilizes the banks.

● Navajo Sandstone and Potential Glen Canyon 

Dam Failure. The Glen Canyon Dam is anchored 

in the relatively porous Navajo Sandstone. 

The spillways have been engineered to prevent 

cavitation and eliminate the potential for water 

flowing over the dam. Should dam failure occur, 

the Colorado River channel would be scoured 

and downstream communities, archeological sites, 

and riparian ecosystems would be damaged or 

destroyed. 

This GRI report was written for resource managers 

to support science-informed decision making. It 

may also be useful for interpretation. The report was 

prepared using available geologic information, and the 

NPS Geologic Resources Division conducted no new 

fieldwork in association with its preparation. Sections 

of the report discuss distinctive geologic features and 

processes within Glen Canyon National Recreation 

Area, highlight geologic issues facing resource 

managers, describe the geologic history leading to 

the present-day landscape, and provide information 

about the GRI GIS data. Posters (in pocket) illustrate 

these data. The Map Unit Properties Tables (in pocket) 

summarize report content for each geologic map unit.

xiii

Products and Acknowledgments

The NPS Geologic Resources Division partners with institutions such as Colorado State University, 

the US Geological Survey, state geological surveys, local museums, and universities to develop GRI 

products. This chapter describes those products and acknowledges contributors to this report.

GRI Products

The objective of the Geologic Resources Inventory is 

to provide geologic map data and pertinent geologic 

information to support resource management and 

science-informed decision making in more than 

270 natural resource parks throughout the National 

Park System. To realize this objective, the GRI team 

undertakes three tasks for each natural resource park: 

(1) conduct a scoping meeting and provide a summary 

document, (2) provide digital geologic map data in a

geographic information system (GIS) format, and

(3) provide a GRI report (this document). These

products are designed and written for nongeoscientists.

Scoping meetings bring together park staff and geologic 

experts to review and assess available geologic maps, 

develop a geologic mapping plan, and discuss geologic 

features, processes, and resource management issues 

that should be addressed in the GRI report. Following 

the scoping meeting, the GRI map team converts the 

geologic maps identified in the mapping plan (“source 

maps”) to digital geologic map data in accordance with 

the GRI data model. After the map is completed, the 

GRI report team uses these data, as well as the scoping 

summary and additional research, to prepare the GRI 

report. 

The compilation and use of natural resource 

information by park managers is called for in the 1998 

National Parks Omnibus Management Act (section 

204), 2006 National Park Service Management 

Policies, and the Natural Resources Inventory and 

Monitoring Guideline (NPS-75). The “Additional 

References” chapter and Appendix B provide links to 

these and other resource management documents and 

information.

Additional information regarding the GRI, including 

contact information, is available at http://go.nps.gov/gri. 

The current status and projected completion dates of 

products are available at http://go.nps.gov/gri_status.

Acknowledgments

Additional thanks to: Sarah Doyle (Glen Canyon 

National Recreation Area) for her list of geohazards; 

Grant Willis, Tyler Knudsen, Doug Sprinkel, John 

Spence, and Vincent Santucci for their excellent 

reviews and photograph contributions; John 

Burghardt (NPS Geologic Resources Division) for his 

updated AML database; Steve Simon, Julia Brunner, 

and Eric Bilderback (NPS Geologic Resources 

Division) for their review comments and discussion 

regarding mineral leases, hazards, and risk; and Trista 

Thornberry-Ehrlich (Colorado State University) 

for producing many of the graphics in this report. 

Thanks to the Utah Geological Association (Stephanie 

Carney and Jason Blake) for permission to reproduce 

photographs from Netoff et al. (2010). Betsy Scroggs

(Glen Canyon National Recreation Area) provided NPS 

photographs taken by Bob Moffitt. 

The Utah Geological Survey completed mapping for 

Glen Canyon National Recreation Area (and other Utah 

NPS units) with funding from the GRI program.

Review

Doug Sprinkel (Utah Geological Survey)

Grant Willis (Utah Geological Survey)

Tyler Knudsen (Utah Geological Survey)

John Spence (NPS Glen Canyon Recreation Area)

Jason Kenworthy (NPS Geologic Resources Division)

Vincent Santucci (NPS Geologic Resources Division)

Editing

Rebecca Port (NPS Geologic Resources Division)

Report Formatting and Distribution

Jason Kenworthy (NPS Geologic Resources Division)

Rebecca Port (NPS Geologic Resources Division)

Source Maps

Compiled by Utah Geological Survey; maps published 

by Utah Geological Survey, US Geological Survey, and 

Canyonlands Natural History Association

GRI Digital Geologic Data Production

James Chappell (Colorado State University)

Heather Stanton (Colorado State University)

Ron Karpilo (Colorado State University)
xiv

GRI Map Posters Design

James Winter (Colorado State University)

GRI Map Posters Editing

Georgia Hybels (Colorado State University)

Rebecca Port (NPS Geologic Resources Division)

Jason Kenworthy (NPS Geologic Resources Division)
Geologic Setting and Significance

This chapter describes the concept of geologic heritage, park significance, fundamental resources, the 

regional geologic setting, and summarizes connections among geologic resources, other park resources, 

and park stories.

1

Geologic Heritage

America’s geologic heritage (geoheritage) encompasses 

the geologic features, landforms, and landscapes 

integral to our country’s history and culture. As in 

so many of our national parks, the geologic features 

in Glen Canyon National Recreation Area inspire a 

sense of awe and wonder, and the preservation of 

these features enriches a full range of values including 

scientific, aesthetic, cultural, ecosystem, educational, 

recreational, tourism, and many others.

Everybody needs beauty as well as bread, places 

to play in and pray in, where nature may heal 

and give strength to body and soul. 

– John Muir, 1912

At the turn of the twentieth century, visionaries like 

John Muir recognized the value of our geoheritage. 

More than scenery, these iconic sites offered the 

opportunity to interact with a landscape shaped by 

the dynamic forces and interminable processes of 

nature and to reflect and grow as individuals and as a 

culture. The streams and rivers are as much a part of 

us as the blood that flows in our veins. The majestic 

mountains speak to the beauty of our souls just as the 

vast horizons of the prairies speak to the expansion of 

our consciousness. Today’s visitor that looks out over 

the plateaus, mesas, narrow canyons, and buttes that 

collectively define Glen Canyon National Recreation 

area is as awestruck with the glory and power of nature 

as were the first visitors to the canyon more than 11,000 

years ago. Our geoheritage reminds us that we are part 

of a much larger community, a community that includes 

not only those with whom we interact but the land, as 

well.

The American landscape of mountains, plateaus, plains, 

volcanoes, glaciers, canyons, and beaches is one of the 

most diverse on Earth. Much of the history of Earth is 

written in the geodiversity of Glen Canyon National 

Recreation Area. The ebb and flow of entire continents, 

the rise and erosion of mountain ranges, and the 

evolution of first organisms to today’s ecosystems 

is documented in the rocks that grace the cliffs and 

canyon walls. Included in that history are the seeds of 

our own present-day culture, the hopes and dreams of 

all who have gone before, and the natural processes that 

are destined to shape the landscapes upon which future 

generations will stand and for a moment, pause and 

reflect.

Today, our open spaces are more precious than 

ever—and it’s more important than ever that we 

come together to protect them for the next

generation. – President Barack Obama, 2011

Refer to http://go.nps.gov/americasgeoheritage and the 

publication America’s Geologic Heritage: An Invitation 

to Leadership (National Park Service and American 

Geosciences Institute 2015) for details about geologic 

heritage and values.

Park Significance and Fundamental Resources

Glen Canyon National Recreation Area was established 

in order to preserve and protect this geodiversity and 

make it available for public enjoyment through both 

land- and water-based recreational activities. The 

recreation area “protects scenic, scientific, natural, and 

cultural resources on Lake Powell, the Colorado River, 

its tributaries, and surrounding lands” (National Park 

Service 2014a).

The significance of Glen Canyon National Recreation 

Area is stated as follows in the 2014 Foundation 

Document (National Park Service 2014a):

● The Colorado River and its many tributaries,

including the Dirty Devil, Paria, Escalante, and San

Juan rivers, carve through the Colorado Plateau to

form a landscape of dynamic and complex desert

and water environments.

● The vast, rugged landscapes of Glen Canyon

National Recreation Area provide an unparalleled

spectrum of diverse land- and water-based
2

recreational opportunities for visitors of wideranging interests and abilities.

● Glen Canyon National Recreation Area preserves 

a record of more than 10,000 years of human 

presence, adaptation, and exploration. This 

place remains significant for many descendant 

communities, providing opportunities for people to 

connect with cultural values and associations that 

are both ancient and contemporary.

● The deep, 15-mile-long, narrow gorge below the 

dam provides a glimpse of the high canyon walls, 

ancient rock art, and a vestige of the riparian and 

beach terrace environments that were seen by John 

Wesley Powell’s Colorado River expedition in 

1869, providing a stark contrast to the impounded 

canyons of Lake Powell.

Heritage resources, Lake Powell, the landscape, 

paleontology, water, and wilderness are among 

the fundamental resources and values identified in 

Glen Canyon National Recreation Area (National 

Park Service 2014a). Heritage resources include 

archeological and historic sites, cultural landscapes, 

Figure 1. Physiographic provinces of the western United States. Glen Canyon National Recreation Area (bright green 

area) lies within the Colorado Plateau province. There are many other National Park System areas on the plateau, 

some of which are labelled. Compiled by Jason Kenworthy and Philip Reiker (NPS Geologic Resources Division) from 

ESRI Arc Image Service, National Geographic Society TOPO Imagery.
3

and traditional cultural properties that illustrate the 

connection of people with the landscape. By surface 

area, Lake Powell is the largest human-constructed 

reservoir in the United States. The rugged water- and 

wind-carved canyons, buttes, mesas, rivers, seeps, 

springs, and hanging gardens provide diverse habitats 

for a variety of endemic, rare, and relict plant and 

animal communities. Fossils found in Glen Canyon 

National Recreation Area continuously add to the 

scientific understanding of the past. Water quality and 

quantity is essential for public outdoor recreational 

use and enjoyment and for sustaining terrestrial and 

aquatic life in the high desert. The proposed and 

potential wilderness areas offer a variety of culturally 

and ecologically unique landscapes where visitors can 

experience that character and solitude of wilderness 

within a recreation area (National Park Service 2014a).

Geologic Setting

From northeast to southwest, Glen Canyon National 

Recreation Area extends from the Orange Cliffs in Utah 

to Lees Ferry in northernmost Arizona (plate 1;

fig. 1). The San Juan Arm of the park follows the San 

Juan River eastward from Glen Canyon to Goosenecks 

State Park in southeastern Utah. The largest National 

Park Service unit in Utah, Glen Canyon National 

Recreation Area protects more than 506,000 ha 

(1.25 million ac) of sedimentary rocks that represent 

approximately 300 million years of Earth history 

(Anderson et al. 2010). Approximately 51% of the 

recreation area consists of 238,301 ha (588,855 ac) 

of proposed wilderness and 19,811 ha (48,955 ac) of 

potential wilderness. 

Glen Canyon National Recreation Area shares its 

borders with public lands administered by the National 

Park Service and the Bureau of Land Management 

(BLM), as well as the Navajo Nation. National Park 

Figure 2. Photograph of Reflection Canyon in Lake Powell, Glen Canyon National Recreation Area. Sedimentary rock 

forms the landscape surrounding Lake Powell. Many visitors explore the lake and side canyons via houseboat. National 

Park Service photograph by Gary Ladd, available at https://www.nps.gov/glca/learn/photosmultimedia/photogallery.htm

(accessed 24 June 2016).
4

Figure 3. Geologic time scale. The divisions of the geologic time scale are organized stratigraphically, with the oldest 

divisions at the bottom and the youngest at the top. Time periods representing the strata mapped in Glen Canyon 

National Recreation Area are in green. GRI map abbreviations for each time division are in parentheses. Compass 

directions in parentheses indicate the regional locations of events. Boundary ages are millions of years ago (MYA). 

National Park Service graphic using dates from the International Commission on Stratigraphy

(http://www.stratigraphy.org/index.php/ics-chart-timescale; accessed 7 May 2015).
5

Figure 4. Stratigraphic column for Glen Canyon Recreation Area and vicinity. The lithology column includes sandstone 

(dots), shale (dashes), siltstone (dots and dashes) and limestones (brick-like pattern). It also indicates weathering 

patterns with coarser-grained, more erosion-resistant rocks (i.e., sandstone) to the right and less-resistant rocks (i.e., 

shale) to the left. The wavy lines represent regional unconformities (TR-1, TR-3, J-1, J-3, J-5, K-0), which are explained 

in the “Unconformities” section. Note: Many rocks mapped as Page Sandstone are now recognized as the Temple Cap 

Formation (see “Unconformities” section). Photographs: (1) View north from Dangling Rope Marina. (2) View east near 

Red Canyon. (3) Stillwater Canyon, Green River. (4) Junction of Dirty Devil and Colorado rivers, near Hite Crossing. (5) 

Confluence of the Green and Colorado rivers, view up Colorado River. Photographs and stratigraphic column are from 

Anderson et al. (2010, figure 4). Column redrafted by Trista Thornberry-Ehrlich (Colorado State University). 
6

System units that border the recreation area include 

Grand Canyon National Park, Capitol Reef National 

Park, Canyonlands National Park, and Rainbow 

Bridge National Monument (plate 1; fig. 1). Geologic 

Resources Inventory reports are available for Capitol 

Reef and Canyonlands national parks and Rainbow 

Bridge National Monument, and the report for Grand 

Canyon National Park is in progress as of August 2016

(KellerLynn 2005; Graham 2006a, 2009). The reports 

are available on the National Park Service Geologic 

Resources Inventory publications website 

http://go.nps.gov/gripubs. BLM administered areas 

include the Grand Staircase-Escalante and Vermilion 

Cliffs national monuments and the Paria CanyonVermilion Cliffs Wilderness. The Navajo Indian 

Reservation borders the recreation area to the southeast 

(plate 1). 

Lake Powell, by volume the second largest reservoir in 

the United States (plate 1), began filling when the gates 

of Glen Canyon Dam closed in 1963 and reached its 

full capacity (referred to as “full pool”) of 32.336 km3

(7.7578 mi3) of water in 1980. At full pool, the reservoir 

is 299 km (186 mi) long with 3,150 km (1,960 mi) of 

shoreline that wraps around 96 major side canyons 

(fig. 2). Lake Powell accounts for 14% of the total area 

of Glen Canyon National Recreation Area and 80% of 

the Colorado River Storage Project (US Department of 

the Interior 2008). 

Glen Canyon National Recreation Area is part of 

the Colorado Plateau, a physiographic province that 

covers roughly 340,000 km2 (130,000 mi2) of Colorado, 

Utah, Arizona, and New Mexico (fig. 1). Climate on 

the Colorado Plateau varies from arid at its lowest 

elevations, semi-arid at intermediate elevations, and 

humid at higher elevations. The rugged topography of 

the region includes broad plateaus and mesas, steep 

narrow canyons, and the Navajo and Henry Mountains 

that range in elevation from 2,400 m (8,000 ft) to 

3,540 m (11,600 ft) above sea level (Anderson et al. 

2010; John Spence, Glen Canyon National Recreation 

Area, Chief Scientist and Terrestrial Natural Resources 

Branch Chief, written communication, 9 December 

2015). These dome-shaped mountains owe their origin 

to world-renowned igneous intrusions known as 

laccoliths. 

Glen Canyon National Recreation Area contains over 

3,000 m (10,000 ft) of sedimentary rocks that were 

deposited during the Pennsylvanian and Permian 

periods of the Paleozoic Era and throughout the 

Mesozoic Era (figs. 3 and 4). Bedrock consists of both 

clastic and carbonate sedimentary rock types (fig. 4). 

Sediment transported into Lake Powell by the Colorado 

River and its tributaries comes primarily from the friable 

sandstone, shale, and mudstone of the sedimentary 

strata on the Colorado Plateau. Unconsolidated river 

gravels eroded from the Rocky Mountains include 

all three basic rock types: sedimentary, igneous, and 

metamorphic. 

Geologic Significance and Connections

The extensive exposures of Mesozoic rocks in Glen 

Canyon National Recreation Area may represent the 

best overall Mesozoic stratigraphic section in the 

National Park Service.

The landscape of the Colorado Plateau transformed 

from a region of shallow seas in the Paleozoic Era more 

than 300 million years ago to terrestrial and coastal 

environments in the Mesozoic Era (~252 million–66 

million years ago). The strata in Glen Canyon National 

Recreation Area document this transition from open 

marine and marginal marine environments to vast 

sand dune-covered deserts and river systems. Fossils 

preserved in the strata also illuminate this transition 

as abundant marine invertebrate fauna gave way 

to terrestrial plants, reptiles, and dinosaurs. These 

shifting environments were the result of tectonic plate 

movements that caused continents to collide and 

separate, climates to change, sea levels to rise and fall, 

and mountains to form.

Collisions between oceanic plates and the North 

American continent have deformed the western margin 

of North America since the Paleozoic, yet the Colorado 

Plateau has remained a relatively rigid lithospheric block 

during these millions of years of deformation. Tectonic 

activity folded and faulted the continental margin into 

a north–south-trending mountain range approximately 

140 million years ago, deformed the continental interior 

into the Rocky Mountains about 70 million to 35 

million years ago, and began pulling apart Earth’s crust 

to form the Basin-and-Range province about 35 million 

years ago. However, strata on the Colorado Plateau, 

including the bedrock in Glen Canyon National 

Recreation Area, sustained relatively mild deformation, 

being bent and folded into broadly warped anticlines 

(convex folds) and regional monoclines (one-limbed 
7

folds in relatively flat-lying strata) (fig. 5). Glen Canyon 

National Recreation Area also contains a variety of 

unconsolidated Quaternary deposits that range in size 

from clay-size particles to house-size boulders (table 1). 

Millions of years are missing between bedrock in Glen 

Canyon National Recreation Area and the overlying 

unconsolidated sediments. This gap in time is known as 

an unconformity, which represents a period of nondeposition and/or erosion of previous strata (see the 

“Geologic Features and Processes” chapter). 

Dating the Colorado River terrace deposits and the 

carving of the Grand Canyon and Glen Canyon has 

been the focus of spirited debate for many years (e.g., 

Willis 1992; Hanks et al. 2001; Willis and Biek 2001; 

Garvin et al. 2005; Karlstrom et al. 2007; Cook et 

al. 2009; Pederson 2009). The alluvial deposits and 

associated river terraces in Glen Canyon National 

Recreation Area have helped constrain the incision of 

Glen Canyon to the past one million years (Garvin et al. 

2005; Anderson et al. 2010; tables 1 and 2 in Willis and 

Ehler, in preparation; see glca_geology.pdf in GRI GIS 

data). 

Glen Canyon had been visited by humans for about 

11,500 years before it was drowned by Lake Powell 

(table 2; National Park Service 2015a). Although not 

every cultural period is well-represented, prehistoric 

artifacts found in the recreation area document human 

occupation beginning with Clovis and Folsom nomads 

during the Paleoindian period (11,500 BCE–8,050 BCE) 

and extending to the first Spanish explorers in 1540 

CE during the Protohistoric period (1500 CE–1850 

CE) (table 2; Geib and Fairley 1997; Tweet et al. 2009; 

National Park Service 2015a). 

The Historic period begins with the 1776 expedition 

of Spanish priests, Father Dominguez and Father 

Escalante, who provided the first written record of Glen 

Canyon (National Park Service 2015a). Their grueling 

expedition had bypassed the canyon country on their 

way from Santa Fe to California, but on their return 

trip, they arrived at the confluence of the Colorado and 

Paria rivers, downstream from the current Glen Canyon 

Dam. Unable to cross the Colorado at the mouth of 

the Paria River, they eventually chopped steps in the 

sandstone wall at Padre Creek, led their pack animals 

Figure 5. Exaggerated geologic cross-sections for Glen Canyon National Recreation Area. The cross-sections illustrate 

the relatively undeformed nature of the strata with broad anticlines (A-shaped folds) and synclines (U-shaped 

folds). The Navajo Mountain laccolith in cross-section B-B’ cuts Lower Jurassic-Upper Triassic strata, indicating that 

emplacement of the igneous unit occurred after the Late Jurassic. Cross-sections from Anderson et al. (2010, figure 5).
8

to the banks of the Colorado, and crossed where the 

river was wide and shallow. Today, this Crossing of 

the Fathers lies beneath Padre Bay, but an inscription 

carved into the sandstone wall reads “paso por aqui” 

(passed by here) with the date 1776, which may have 

been left behind by Fathers Dominguez and Escalante 

(DesertUSA 2015; John Spence, written communication 

9 December 2015).

About 100 years after the Dominguez-Escalante 

expedition, Major John Wesley Powell, the one-armed 

geologist and American Civil War veteran, led a crew of 

nine men on the first-ever scientific expedition through 

the Colorado and Green rivers. In May 1869, Powell left 

Green River, Wyoming, and on July 28, he and his men 

entered a canyon decorated with “carved walls, royal 

arches, glens, alcove gulches, mounts, and monuments” 

(Major John Wesley Powell quoted in Anderson et al. 

2010, p. 309). The expedition named this canyon “Glen 

Cañon.” Ironically, the reservoir that bears his name has 

drowned the rapids and canyons through which Powell 

navigated, as well as many of the natural features that 

Powell documented. 

Railroad workers further explored the Colorado River 

in hopes of extending a line from Grand Junction, 

Colorado, to the Gulf of California, but funding for 

their project did not materialize. In 1873, the Church of 

Jesus Christ of Latter-day Saints (Mormon Church) sent 

John D. Lee to the confluence of the Colorado and Paria 

rivers with instructions to build and operate a ferry. 

Various operators (with a variety of ferryboats; fig. 6) 

maintained a ferry at Lees Ferry until Navajo Bridge was 

completed in 1929 to accommodate automobile traffic. 

Table 1. Summary of unconsolidated deposits mapped in Glen Canyon National Recreation Area.

Age Unit (map symbol) Description

(see Unconsolidated Map Unit Properties Table for more detail)

Holocene

Artificial fill & disturbed areas (Qfd) Gravel, sand, earth-fill, and large disturbed areas

Concrete fill in Glen Canyon Dam (Qfdm) Concrete fill used in the construction of Glen Canyon Dam

Pleistocene 

to Holocene

Alluvial 

deposits

Alluvial deposits (Qa, Qal, Qal1, 

Qat, Qaty, Qat2-13, Qag, Qagm, 

Qago)

Boulder to pebble gravel, sand, silt, and clay deposited in Colorado and San Juan rivers 

and their tributaries, on broad alluvial fan surfaces, and in terrace remnants. Clasts

generally reflect local lithologies

Mixed environment 

deposits

Alluvial and colluvial deposits 

(Qac, Qaco)

Boulder to clay-sized sediment deposited in small ephemeral drainages. Moderately to

poorly sorted. Includes colluviu

Alluvial and eolian deposits 

(Qae, Qae2, Qae3, Qaeo)

Boulder to clay-sized alluvial sediments and windblown sand and silt. Deposited by in

streams, washes, and low slopes

Alluvial fan and stream, eolian, 

and colluvial deposits (Qaec)

Boulder to clay-sized deposits on low slopes below cliff- and ledge-forming units where 

stream gradients are reduced

Eolian and alluvial deposits (Qea, 

Qeao)

Sand, silt, clay deposited by wind mixed with stream-deposited pebbles and cobbles and 

capped by a thick calcic soil (caliche) that forms a resistant bench

Lacustrine deposits (Ql) Thinly laminated silt, very fine-grained sand, peat, and clay partly covered by eolian silt

Spring tufa deposits (Qst) Calcareous tufa deposited by springs. Tufa cements bedrock and talus rubble, colluvium,

and other surficial deposits

Eolian sand (Qes) Very well-sorted, well-rounded, fine- to medium-grained quartz sand. Deposited by wind

in sheets, mounds, and dunes

Mass movement deposits

Landslide and slump deposits 

(Qms, Qmsh)

Extremely poorly sorted, angular, massive blocks to clay-size material that slumped or 

flowed down slopes

Slump blocks (Qmsb)

Intact to partially intact blocks of rock as much as 2.7 km (1.5 mi) long that hav

slumped downslope. Blocks commonly rotate backwards and dip toward the nearby

cliff

Talus deposits (Qmt) Broken, angular rockfall debris at the base of steep slopes

Landslide, slump, and talus 

deposits, undifferentiated (Qmst) Undifferentiated Qms, Qmsh, Qmsp, Qmt, and Qmte deposits

Talus deposits with eolian sand 

mantle (Qmte)

Similar to Qmt deposits except commonly covered by moderate to large amounts of 

eolian sand

Pleistocene Alluvial deposits (Qatg8, Qatg9) Older alluvial river terrace and locally derived gravel deposits
9

Settlers in the San Juan Valley continued to find more 

suitable ferry routes across the Colorado River. An early 

river crossing in Hole-In-The-Rock at the confluence 

of the Colorado and Escalante rivers was superseded 

by a better crossing found by Charles Hall about 56 

km (35 miles) upstream. Travelers were ferried across 

Hall Crossing until Cass Hite found and developed 

another, still more accessible crossing. The town and 

ferry at Hite, Utah, remained operational until they 

were flooded by the rising waters of Lake Powell.

In 1956, Congress authorized Glen Canyon Dam 

to provide water storage in the upper Colorado 

River Basin. The dam is managed by the Bureau of 

Reclamation. Several major tributaries such as the 

Green, Yampa, White, Dolores, Dirty Devil, and 

San Juan rivers provide water to Lake Powell. At full 

pool, the surface elevation of the reservoir is 1,128 

m (3,700 ft) above mean sea level. Since 2000, the 

average annual surface elevation of the reservoir 

has fluctuated from a high of 1,121.09 m (3,678.11 

ft) above sea level in 2000 to a low of 1,091.15 m 

(3,579.88 ft) in 2004 (Lake Powell Water Database 

2016). The NASA Earth Observatory website 

includes a feature showing water levels of Lake 

Powell over time (http://earthobservatory.nasa.gov/

Features/WorldOfChange/lake_powell.php). Most 

of the water (85%) from Lake Powell is dedicated to 

agricultural production. The rest goes to urban areas 

in California, Arizona, and Nevada.

Table 2. American Indian history in Glen Canyon National Recreation Area.

Cultural Period Time Geologic Heritage Connection

Paleoindian 11,500 BCE – 8,050 BCE Clovis and Folsom nomadic hunters left a few projectile points that had been fashioned from 

bedrock

Archaic 8,050 BCE – 400 BCE Broad-based hunting/gathering period. Many distinctive artifacts, such as sandals. Maiz

agriculture began about 2,600 years ago

Preformative 

(Basketmaker II) 400 BCE – 500 BCE Artifacts are sparse in Glen Canyon. Pottery has yet to be developed. The bow and arrow arintroduced late in the period

Formative 500 CE – 1300 CE

Fremont and Puebloan cultures. Plethora of artifacts from the recreation area. Period i

characterized by agriculture, permanent or semi-permanent habitations, and pottery. The Fremont

culture occupied the region north of the Colorado River, while the ancestral Puebloans, who 

include today’s Hopi Indians, lived south of the river. The ancestral Puebloans leave the Four

Corners area at the end of the period

Late Prehistoric 1300 CE – 1500 CE Paiute groups expanded into Glen Canyon, but this period is poorly understood within the 

recreation area

Protohistoric 1500 CE – 1850 CE

Artifacts are sparse, but some evidence suggests that Navajo, who migrated into the area from 

northwestern Canada and eastern Alaska around 1400 CE, Paiute and Hopi visited Glen Canyon 

prior to the arrival of the Spanish in 1540 CE

Information from Geib and Fairley (1997), Tweet et al. (2009), and National Park Service (2015a

Figure 6. Historic photograph of ferryboat at Lees Ferry. John 

D. Lee established the first ferry at the confluence of the

Colorado and Paria rivers in the 1870s. Ferries operated there

until Navajo Bridge opened in 1929. National Park Service

photograph available at

https://www.nps.gov/glca/learn/photosmultimedia/

photogallery.htm (accessed 24 June 2016).

11

Geologic Features and Processes

This chapter describes noteworthy geologic features and processes in Glen Canyon National Recreation 

Area.

During the 1999 scoping meeting (NPS Geologic 

Resources Division and Natural Resources Information 

Division 1999) and 2015 conference call, participants 

(see Appendix A) identified geologic features and 

processes from the following categories:

● Landscape Features

● Sedimentary Rocks and Sedimentary Rock Features

● Unusual Sedimentary Rock Features

● Paleontological Resources

● Caves and Karst

● Paleosols

● Unconformities

● Folds and Faults

● Joints

● Laccoliths

● Unconsolidated Surficial Deposits

● Hite Delta Geomorphic Features

● Economic Minerals

● Geologic type sections

Features within these categories, and the processes 

responsible for them, capture the rich geodiversity of 

the recreation area.

The National Park Service Foundation Document 

(National Park Service 2014a) outlines the significance, 

fundamental resources, and other important resources 

within the recreation area. Many of these have 

connections to geology (see “Geologic Setting and 

Significance” chapter).

This chapter utilizes much information from, and 

follows the terminology of, the Glen Canyon National 

Recreation Area chapter (Anderson et al. 2010) in 

Geology of Utah’s Parks and Monuments (Utah 

Geological Association, 3rd edition). A companion 

geologic field trip guide to the recreation area is 

available as Chidsey et al. (2012).

Resource management issues associated with these 

features and processes are discussed in the next chapter.

Landscape Features

Colorful bluffs, mesas, buttes, canyons, and a myriad 

of other spectacular landscape features dominate the 

viewshed in Glen Canyon National Recreation Area 

(table 3). These iconic features are some of the more 

accessible and popular features of their type in the 

world, and they were visited by 2.5 million visitors in 

2015 (National Park Service 2015b). Fittingly, they are 

considered fundamental resources by the NPS and 

are summarized in the Foundation Document for the 

recreation area (National Park Service 2014a). A variety 

of resource management issues exist for these iconic 

features and are summarized in the following “Geologic 

Resource Management Issues” chapter.

Plateaus, Mesas, and Buttes

The plateaus, mesas, and buttes that characterize the 

Colorado Plateau differ from one another primarily in 

size. A plateau is usually higher and more extensive than 

a mesa, which is more extensive than a butte. Plateaus 

are generally at least 150 m (500 ft) above the adjacent 

countryside or sea level, relatively flat, and bordered 

on at least one side by an abrupt descent. Plateaus 

are often dissected by steep canyons or valleys. Glen 

Canyon National Recreation Area is bordered by the 

Kaiparowits Plateau to the northwest, the Rainbow 

Plateau to the southeast, and the Red Rock Plateau to 

the east (plate 1).

A mesa is an isolated flat-topped landmass bounded 

on all sides by steep scarps and capped by a layer of 

resistant rock. Some of the mesas in the recreation area 

are included in table 3. The erosion-resistant Navajo 

Sandstone (geologic map unit Jn) caps the majority of 

the mesas in the recreation area (table 3).

A butte is often an isolated remnant of an eroded mesa 

(fig. 7). Buttes have steep slopes or cliffs, a resistant 

caprock, and a summit that may be flat-topped, craggy, 

rounded, pointed, or otherwise irregular. Many of the 

buttes in Glen Canyon National Recreation Area are 

carved in the Kayenta (Jk), Chinle (TRc), and Moenkopi 

(TRm) formations (table 3). Persistent erosion whittled 

the original plateaus and mesas of less-resistant strata 

into buttes.
12

Table 3. Landscape features in Glen Canyon National Recreation Area.

Feature Examples and/or Locations Formations (map symbol)

Mesas

Dry Mesa (southern end of Cataract Canyon) Cedar Mesa Sandstone (Pcm)

Good Hope Mesa (Glen Canyon)

Navajo Sandstone (Jn)

Hall Mesa (north of Bullfrog visitor center)

Iron Top Mesa (southwest of Halls Crossing)

Grey Mesa (east of Hole-in-the-Rock)

Wilson Mesa (east of Hole-in-the-Rock)

Grand Bench (borders of Last Chance Bay) Morrison Formation, Salt Wash Member (Jms) Romana Mesa (east of Warm Creek Bay)

Buttes (fig. 7

Buttes of the Cross (Millard Canyon)

Cleopatras Chair (Millard Canyon) Kayenta Formation (Jk)

Ekker Butte (east of Panorama Pt Overlook)

Bagpipe Butte (Bagpipe Butte Overlook) Chinle Formation, upper members (TRcu)

Castle Butte (mouth of Blue Notch Canyon) Chinle Formation, Church Rock Member (TRcc)

Teapot Rock (south of Teapot Canyon) Moenkopi Formation (TRm)

Cliffs (fig. 7

Navajo Point Straight Cliffs Formation (Ksj, Ksl)

Bullfrog area; shoreline along Last Chance, Padre, and 

Wahweap Bays Entrada Sandstone (Je)

Dominates the shoreline of Lake Powell Navajo Sandstone (Jn)

Good Hope Bay, San Juan Arm, The Rincon Wingate Sandstone (JTRw)

Lees Ferry/Navajo Bridge area Kaibab Formation (Pk), Coconino Sandstone (Pco)

Northern part of recreation area White Rim Sandstone (Pwr)

San Juan River canyon; Colorado River canyon (east of Hite 

Crossing) Cedar Mesa Sandstone (Pcm)

The Horn limestone (San Juan River canyon) Paradox Formation (PNp)

Ledges/Benches and Slopes 

(fig. 7

Navajo Point Tropic Shale (Kt)

Between Wahweap Bay and Fiftymile Mountain Dakota Formation (Kd)

Between Wahweap Bay and Dangling Rope Marina; 

between West and Wetherill Canyons Morrison Formation (Jmb, Jms, Jsmt)

Bullfrog Bay, near Dangling Rope Marina, upper part of 

Rock Creek Carmel Formation (Jc)

Near Glen Canyon Dam Page Sandstone (Jp)

Good Hope Bay, San Juan Arm, The Rincon Kayenta Formation (Jk), Chinle Formation (TRc)

Lower Cataract Canyon Cutler Group: lower Cutler beds (PPNcl)

Near Hite, San Juan Arm, Escalante Canyons Moenkopi Formation (TRm)

San Juan River canyon (The Horn, Hite Crossing, Clay Hills) Organ Rock Formation (Po), Halgaito Formation (PPNhg), 

Honaker Trail Formation (PNht, PNhtu, PNhtl)

South of Navajo Bridge Toroweap Formation (Pt)

Slickrock (fig. 8) Associated with cliffs Navajo Sandstone (Jn), Entrada Sandstone (Je), Cedar

Mesa Sandstone (Pcm)

Slot Canyons Many slot canyons branch from Lake Powell Kayenta Formation (Jk), Navajo Sandstone (Jn)

Alcoves* (fig. 9) Escalante Canyon* Navajo Sandstone (Jn), Cedar Mesa Sandstone (Pcm) Main channel of Lake Powell

Hanging Gardens* Side drainages of Colorado River (i.e., Ribbon Canyon an

Knowles Canyon [fig. 9]

Contact of the Navajo Sandstone (Jn) and the Kayenta 

Formation (Jk)

* Indicates landscape features identified as “classic geologic sites” in Anderson et al. (2010
13

Cliffs, Ledges, and Slopes

The strata in Glen Canyon National Recreation Area 

form a landscape of cliffs, ledges, and slopes as a result 

of their lithology and resistance to erosion (fig. 4). On 

the arid Colorado Plateau, sandstone and limestone 

are more resistant to weathering and erosion than 

siltstone and shale (table 3). Cliffs composed of 170–340 

m- (550–1,100 ft-) thick Navajo Sandstone (Jn), for 

example, dominate the central part of Glen Canyon 

National Recreation Area. By comparison, the 150–230 

m (500–750 ft) of less-resistant Tropic Shale (Kt) forms 

slopes along Fiftymile Mountain. 

In units composed of alternating layers of sandstone, 

siltstone, and shale, the topography may take on a 

stair-step like appearance. These transitions may 

reflect a change in depositional environments as well 

Table 3. Landscape features in Glen Canyon National Recreation Area, continued.

Feature Examples and/or Locations Formations (map symbol)

Arches (fig. 10

Annies Canyon Arch (Annies Canyon)

Navajo Sandstone (Jn)

Bement Arch (Davis Gulch)

Bills Arch (Silver Falls Creek)

Broken Bow Arch (Willow Gulch)

Cliff Arch (Coyote Gulch)

Golden Cathedral Bridges (Choprock Bench)

Halls Creek Bridge (Halls Creek Bay)

Hole in the Rock Arch (Fiftymile Point)

Humdinger Arch (Rock Creek Bay)

Jacob Hamblin Arch (Coyote Gulch)

LaGorce Arch (Davis Gulch)

Natural Arch (east of Hans Flat)

Not Bills Arch (Silver Falls Creek)

Overlooked Arch (Rock Creek Bay)

Stevens Natural Arch (Stevens Canyon)

Stove Pipe Arch (East of Pollywog Bench)

Triple Arch (Cottonwood Canyon)

Zane Grey Arch (Explorer Canyon)

Skylight Arch (north of Stud Horse Point) Entrada Sandstone (Je) Wahweap Window (Wahweap Bay) (Je)

Alcove Arch (Rock Creek Bay) Morrison Formation, Salt Wash Member (Jms)

Millard Canyon Arch (Millard Canyon) Moenkopi Formation (TRm)

Natural Bridges (fig. 11

Rainbow Bridge Navajo Sandstone (Jn) Coyote Natural Bridge (Coyote Gulch)

Wiregrass Canyon Bridges Entrada Sandstone (Je)

Badlands Navajo Point area Tropic Shale (Kt)

Hoodoos Stud Horse Point (south of Skylight Arch) Entrada Sandstone (Je), Carmel Formation (Jc)

Entrenched Meanders* (fig

12; cover)

The Rincon* Kayenta Formation (Jk), Navajo Sandstone (Jn)

Horseshoe Bend (south of Glen Canyon Dam) Navajo Sandstone (Jn) 

The Horn (south of Hite) Kayenta Formation (Jk)

Desert Varnish (fig. 9) Cliffs throughout the recreation area Wingate Sandstone (JTRw), Navajo Sandstone (Jn

Sandstone Pipes (fig. 13

Rock Creek Bay

Cookie Jar Butte Entrada Sandstone, lower member (Jel)

Warm Creek Bay

Weathering Pits* (fig. 13) Cookie Jar Butte (Padre Bay)* Entrada Sandstone, lower member (Jel

* Indicates landscape features identified as “classic geologic sites” in Anderson et al. (2010
14

as a change in lithology. For example, the cliffs in the 

Kayenta Formation (Jk) are composed of cross-bedded 

sandstone reflecting an eolian environment, but the 

overlying ledges of sandstone and slopes of mudstone 

reflect deposition in a fluvial-floodplain-lacustrine 

environment.

Within a single formation, changes in weathering 

and landscape patterns may differentiate individual 

members. In the Morrison Formation (Jm), for example, 

the resistant conglomerate and sandstone of the Salt 

Wash Member (Jms) form ledgy cliffs distinct from the 

overlying mudstone slopes of the Brushy Basin Member 

(Jmb). 

Slickrock

Slickrock is an informal term for smooth cliffs and 

steep slopes of sandstone bedrock (fig. 8). Slickrock 

surfaces are not necessarily slick. Rather they are more 

like sandpaper, until they get wet. The term originated 

from early immigrants who found these sloping 

sandstone surfaces a challenge for their horses’ metal 

shoes. In southeastern Utah and Glen Canyon National 

Recreation Area, slickrock surfaces are common in 

the Jurassic Navajo (Jn) and Entrada (Je) sandstones 

and in the Permian Cedar Mesa Sandstone (Pcm) 

(table 3). Slickrock in these three formations form in 

cross-bedded sandstone that represent preserved dune 

fields. As the eolian cross-beds weathered, they formed 

massive knobs and domes and slickrock.

The Navajo Sandstone (Jn) forms domes above vertical 

canyon cliffs. The unit covers about 85% of the central 

part of Glen Canyon National Recreation Area and 

about one-third of the entire surface area of the park 

(Anderson et al. 2010). It dominates the Lake Powell 

shoreline from Rainbow Bridge National Monument 

north to Good Hope Bay.

Abundant outcrops of Middle Jurassic Entrada 

Sandstone are present in the Bullfrog area, between 

Bullfrog and Hansen Creek, and surrounding Last 

Chance, Padre, and Wahweap bays on the western 

shoreline of Lake Powell. The formation has been 

divided into both informal and formal members:

(1) lower member (Gunsight Butte Member),

(2) middle member (Cannonville Member), and

(3) upper member (Escalante Member) (Doelling 

and Davis 1989; Anderson et al. 2010). The lower two 

members are preserved in the southern part of the 

recreation area, and all three have been mapped in the 

northern part (Anderson et al. 2010). Slickrock surfaces 

form primarily in the lower member (Jel; Gunsight 

Butte Member), which is characterized by smooth cliffs 

and rounded domes barren of vegetation.

In the northeastern part of the recreation area and 

along the upper reaches of the San Juan Arm, the 

Early Permian Cedar Mesa Sandstone (Pcm) forms an 

impressive slickrock landscape (Anderson et al. 2010). 

Numerous small drainages dissect the Cedar Mesa 

Sandstone, resulting in extensive slickrock canyons. 

Figure 7. Photograph of buttes, alcoves, and outcrop patterns. Sandstones form cliffs; finer-grained siltstone of the 

Carmel Formation forms slopes. Alcoves have formed in the Entrada Sandstone. The photo shows Boundary and 

Dominguez buttes. Photograph from Anderson et al. (2010, figure 17).
15

Slot Canyons

Southern Utah likely contains the highest density of slot 

canyons in the world. A slot canyon is a narrow canyon 

formed by the vertical incision of rushing water (table 

3). Slot canyons are significantly deeper than they are 

wide. They may be as narrow as 1 m (3 ft) and as deep as 

90 m (300 ft). 

With the uplift of the Colorado Plateau and rapid 

incision by the Colorado River, beginning about 5.5 

million years ago, numerous slot canyons developed 

as tributaries cut into bedrock. As with entrenched 

meanders, many of these canyons cut into the 

relatively soft Cretaceous, Jurassic, and Triassic strata 

(Anderson et al. 2010). Near-vertical and inclined joints 

contributed to the development of slot canyons in the 

recreation area (Anderson et al. 2010). 

Many slot canyons branch away from Lake Powell. 

Kayakers can explore slot canyons, such as Cathedral, 

Cascade, Wetherill, and Face canyons, that have been 

flooded by Lake Powell but are too narrow for power 

boats to enter.

Debris flows and flash floods generated by sudden, 

intense rain storms may pose a threat to hikers in slot 

canyons throughout the Escalante watershed (see the 

“Geologic Resource Management Issues” chapter). 

Alcoves and Hanging Gardens

Alcoves and hanging gardens, considered “classic 

geologic sites” by Anderson et al. (2010), are visible 

along the main channel of Lake Powell and in many 

side canyons, such as Escalante Canyon (table 3). The 

alcoves form as a result of groundwater flow, wind, 

fractures in the rock, and gravity, and most of them are 

Figure 8. Photograph of slickrock in Glen Canyon National Recreation Area. Steep slopes of slickrock and cliffs are 

characteristic features in the recreation area. National Park Service photograph by Bob Moffitt, available online: 

https://www.nps.gov/media/photo/gallery.htm?id=14298A9B-155D-451F-676507C4A4BB767E (accessed 11 September 

2015).
16

found at the contact between the relatively impermeable 

Kayenta Formation (Jk) and the overlying porous and 

permeable Navajo Sandstone (Jn). 

The Kayenta Formation contains silt and clay that fill 

pore spaces in the rock and impede the downward flow 

of groundwater coming from the Navajo Sandstone. 

When groundwater encounters the Kayenta Formation, 

it begins to flow laterally, emerging from the canyon 

walls as seeps and springs. The water dissolves and 

removes the carbonate cement holding the Navajo 

sand grains together, and the loosened grains are blown 

away by the wind. Over time, slabs of rock weaken and 

break away from the cliff, forming a recess or alcove 

(fig. 9). Alcoves, especially those with a spring at the 

Navajo/Kayenta interface, attracted prehistoric visitors. 

Excellent examples of alcoves containing intact cliff 

dwellings dating to the late 13th century are preserved 

in Navajo National Monument, about 60 km (40 mi) 

southeast of Rainbow Bridge National Monument (see 

GRI report by Graham 2007).

Surface water also contributes to alcove formation. 

Vertical fractures or joints in the Navajo Sandstone 

serve as conduits for surface water. Localized pools 

of water in these fractures promote both plant growth 

and animal life (macroscopic and microscopic) which 

increases the acidity of the water and generates 

additional erosion.

The moisture and shade in the alcoves create an ideal 

environment for a variety of plants. These spring-fed 

plants cling to the vertical cliff walls to form hanging 

gardens (fig. 9). Some hanging gardens in Glen Canyon 

Figure 9. Photograph of Navajo Sandstone alcove with a hanging garden in Knowles Canyon, Glen Canyon National 

Recreation Area. Hanging gardens develop where groundwater seeps along an impermeable horizontal bed. Desert 

varnish above the hanging garden has stained some of the cliff a dark brown color. Cross-beds high on the cliff face 

tilt to the south-southeast, indicating paleowind direction in the Navajo erg. Photograph from Anderson et al. (2010, 

figure 26).
17

were drowned by Lake Powell, but many hanging 

gardens are found in the canyons and side drainages 

of the Colorado and San Juan rivers. The lush 

hanging gardens composed of algae, ferns, lilies, 

orchids, grasses, and sedges are in stark contrast to 

the surrounding desert landscape (Everhart 1983; 

Welsh 1989; Anderson et al. 2010). Roots from these 

plants also help to break down the surrounding rock. 

In addition to plants, the hanging gardens contain 

a rich biodiversity of invertebrates (terrestrial and 

aquatic), birds, mammals, and amphibians. 

Although they cover less than 0.1% of Glen 

Canyon National Recreation Area, hanging 

gardens support at least 35 plant species endemic 

to the central-eastern Colorado Plateau (National 

Park Service 2015c; John Spence, Glen Canyon 

National Recreation Area, Chief Scientist and 

Terrestrial Natural Resources Branch Chief, written 

communication, 9 December 2015). These features 

are particularly susceptible to climate change (see 

the “Geologic Resource Management Issues” 

chapter).

Natural Arches

The greatest concentration of natural rock arches 

anywhere in the world dominates the landscape of 

Arches National Park, approximately 40 km (25 mi) 

northeast of the northern boundary of Glen Canyon 

National Recreation Area (see GRI report by Graham 

2004). Over 2,000 arches have been documented in 

Arches National Park, and most of these formed in the 

Entrada Sandstone (National Park Service 2015d). In 

Glen Canyon National Recreation Area, many arches 

developed in the massive Navajo Sandstone (Jn), but 

they also occur in the Entrada Sandstone (Je), Salt Wash 

Member of the Morrison Formation (Jms), and the 

Moenkopi Formation (TRm) (table 3; fig. 10).

The Natural Arch and Bridge Society (NABS) may 

be the only organization dedicated to the study, 

interpretation, and preservation of natural arches and 

bridges (Grant Willis, Utah Geological Survey, geologist, 

written communication, 1 December 2015). The NABS 

defines a natural arch as any rock exposure, regardless 

of size, in which a hole has formed as a result of natural 

processes (NABS 2015). The natural processes that 

produce the hole are primarily processes of erosion, 

which operate on macroscopic and microscopic scales. 

Macroscopic erosion usually involves joints or 

fractures in the rock matrix that formed because of 

tectonic, or catastrophic, processes. Folding caused 

by the Laramide Orogeny, a mountain building event 

that shaped the Rocky Mountains between about 70 

million and 40 million years ago, may have significantly 

contributed to arch formation in Glen Canyon National 

Recreation Area (Grant Willis, written communication, 

1 December 2015). The laccolith intrusion of Navajo 

Mountain may have caused the joints associated with 

Rainbow Bridge.

Once fractures form, they widen through a variety 

of processes. Plant roots may physically enlarge the 

fracture. In winter, water in the cracks may freeze 

and expand and pry the rock apart. The end result 

consists of fragments of the original rock that are now 

susceptible to the forces of gravity. 

On the microscopic scale of erosion, water dissolves 

the crystalline cement holding individual grains 

together. The Navajo and Entrada sandstones, which 

contain the majority of arches in Glen Canyon 

Figure 10. Photograph of Broken Bow arch, Glen Canyon 

National Recreation Area. Carved in Navajo Sandstone (Jn) 

and named for an Indian bow found beneath it in 1930, the 

Broken Bow arch is (2.3 mi) from the Willow Gulch Trailhead 

and stands 52 m (170 ft) tall. Its limbs are as much as 21 m (70 

ft) thick. The opening is 29 m (94 ft) wide and 30 m (100 ft) 

high. Photograph courtesy of Tyler Knudsen, Utah Geological 

Survey.
18

National Recreation Area (table 3), represent ancient 

sand dunes. Sand dunes, ancient or modern, contain 

primarily well-sorted, nearly spherical sand grains and 

lack finer-grained silt and clay particles. Upon burial, 

calcium carbonate precipitated out of groundwater 

and cemented together the sand grains in the Navajo 

and Entrada sandstones. Most of the weathering that 

initially created the arches occurred when the porous 

and fractured sandstones were near the surface, where 

water lingered and had time to dissolve the cement 

(Grant Willis, written communication, 1 December 

2015). 

Every process involved in arch formation includes 

the action of water, gravity, temperature variation, or 

tectonic pressure on rock. Wind, however, is not a 

significant process in arch formation. Wind does not 

remove grains loosened by microscopic erosion, and 

while sandstorms may polish already existing arches, 

they cannot create arches. Detailed information 

regarding the process of erosion relevant to arch 

formation, the various classification schemes, and arch 

types is available on the NABS website (http://www.

naturalarches.org/nabs.htm, accessed 4 January 2016).

Typical of low-humidity desert environments, 

weathering in the Glen Canyon region slowed once 

the rocks were elevated, exposed at the surface, 

and mostly surrounded by air (Grant Willis, written 

communication, 1 December 2015). Rain that falls on 

the arch, or other landscape feature such as a hoodoo, 

fin, or pedestal, is quickly evaporated in the arid climate, 

and in an ironic twist, the remaining salts are reprecipitated, hardening the surface.

Natural Bridges

A natural bridge is one of many types of natural arches 

(NABS 2015). Natural bridges are distinguished 

from arches by having one or more of the following 

attributes:

● Flowing water was a major factor in forming the 

hole.

● Flowing water currently flows through the opening. 

● The bridge was, or still is, used by humans as part of 

a road.

● The bridge looks like a man-made bridge, e.g., it has 

a flat, level top over an arched opening.

A stream flows beneath the 15 m (50 ft) span of Coyote 

Natural Bridge in Coyote Gulch (table 3). The bridge 

formed in Navajo Sandstone (Jn) and is 2.7 km (1.7 

mi) downstream from Jacob Hamblin Arch (table 3). 

Fremont Indian dwellings are on the north canyon 

wall upstream from the bridge, and Fremont Indian 

pictographs are found downstream (Wild Backpacker 

2015). 

The two natural bridges in Wiregrass Canyon formed 

in Entrada Sandstone (Je; table 3). Flood waters from a 

parallel canyon cut through the narrow canyon wall to 

form the natural bridge about 1.6 km (1 mi) south of the 

road. During floods, water still flows under this bridge 

and into Wiregrass Canyon. The second natural bridge 

in Wiregrass Canyon is found near Lake Powell.

The most famous natural bridge in the area is Rainbow 

Bridge in Rainbow Bridge National Monument (fig. 

11). The national monument is adjacent to, and 

administered by staff from, Glen Canyon National 

Recreation Area (plate 1). Bridge Creek, fed by springs 

and runoff from Navajo Mountain, carved Rainbow 

Bridge by eroding through a thin wall of Navajo 

Sandstone (Chidsey et al. 2000a, 2000b; see GRI report 

by Graham 2009).

Streams also flow beneath the three exceptional natural 

bridges in Natural Bridges National Monument, 

approximately 48 km (30 mi) east of Hite and adjacent 

to highway 95. These bridges formed in the Cedar 

Mesa Sandstone (Pcm) (see GRI report by ThornberryEhrlich 2004)

Badlands and Hoodoos

Steep, unvegetated slopes of unconsolidated or poorly 

cemented clay or silt characterize badlands topography. 

The shale and mudstone of the Late Cretaceous 

Tropic Shale (Kt) forms stark badlands topography 

in Glen Canyon National Recreation Area (table 3). 

Exposed at the southern end of Fiftymile Mountain, 

the 150–230 m- (500–750 ft-) thick Tropic Shale 

underlies the sandstone and mudstone of the Straight 

Cliffs Formation (Ksl). Viewed from Dangling Rope 

Marina, these Cretaceous units cap Navajo Point. Many 

landslides occur along the escarpment of Fiftymile 

Mountain because the Tropic Shale is so easily eroded 

(Anderson et al. 2010).

Broad, gently sloped badlands characterize local 

exposures of the Triassic Chinle Formation (TRc) in 

Glen Canyon National Recreation Area and in the 
19

Tununk Shale Member of the Cretaceous Mancos Shale 

(Kmt). The Tununk Shale is roughly equivalent in age to 

the Tropic Shale (Kt), but it is only mapped northwest 

of Bullfrog in the Henry Mountains basin, outside 

the recreation area (see GRI GIS data; Anderson et al. 

2010).

The bizarre columns, pinnacles, and pillars of rock in 

the recreation area are known as hoodoos. Hoodoos are 

the iconic geologic feature of Bryce Canyon National 

Park (see GRI report by Thornberry-Ehrlich 2005). 

Hoodoos result from differential weathering, a process 

in which rocks composed of relatively soft material, 

such as mudstone, erode more easily than harder rocks, 

such as sandstone. Sporadic intense rainfall in the 

high-desert regions of the Colorado Plateau drives the 

differential weathering in the recreation area. Joints 

in the rocks contribute to this differential erosion to 

produce such unusual shapes as the toadstool-shaped 

pinnacles and balanced rocks at Stud Horse Point, 

south of Skylight Arch. 

Entrenched Meanders

A typical meandering stream migrates laterally back 

and forth across its floodplain, cutting sinuous curves 

and bends into easily erodible unconsolidated surface 

sediments. However, if a stream erodes downward 

more rapidly than laterally, its meanders may incise into 

bedrock and become entrenched, unable to migrate 

laterally. Entrenched meanders with tight, curling loops 

are known as goosenecks. 

Vertical downcutting may exceed lateral migration 

across a floodplain as a result of rapid uplift or a 

lowering of a stream’s base level, which is the lowest 

level to which a stream channel can erode (the ultimate 

Figure 11. Photograph of Rainbow Bridge, Rainbow Bridge National Monument. Carved in Navajo Sandstone, Rainbow 

Bridge towers over visitors (yellow arrow) hiking along the stream that flows under the opening. National Park Service 

photograph available: http://www.nps.gov/media/photo/gallery.htm?id=00D6226E-155D-451F-679D6F8C5886A244

(accessed 5 January 2016).
20

base level is sea level). Uplift of the Colorado Plateau 

and rapid incision of the Colorado River beginning 

about 5.5 million years ago caused the Colorado River 

to carve narrow slot canyons and entrenched meanders 

into relatively soft Cretaceous, Jurassic, and Triassic 

strata (Anderson et al. 2010). Tributary drainages, such 

as the Escalante and Dirty Devil rivers, also became 

entrenched as their channels encountered bedrock and 

their canyons deepened in an attempt to keep pace with 

the incision of the Colorado River (Cook et al. 2009; 

Anderson et al. 2010).

Entrenched meanders in Glen Canyon National 

Recreation Area include The Rincon, Horseshoe Bend, 

the Horn, Georges Camp on the Escalante River, and 

many lesser meanders along the rivers (plate 1; fig. 12; 

table 3). Located on the southern plunging nose of the 

Circle Cliffs anticline on the east side of Lake Powell, 

The Rincon, one of the “classic geologic sites” of 

Anderson et al. (2010), stands 180–230 m (600–750 ft) 

above its now-abandoned channel. Stratigraphically, the 

Chinle Formation (TRc) anchors the butte at lake level 

followed by the Wingate Sandstone (JTRw), the Kayenta 

Formation (Jk) which caps the butte, and some local 

exposures of Navajo Sandstone (Jn) above the Kayenta 

(Anderson et al. 2010). Several thousand years ago, the 

Colorado River shortened its length by 10 km (6 mi) 

by carving its way through the Wingate Sandstone and 

cutting off The Rincon meander.

The Colorado River eroded vertically through the 

Upper Member of the Moenkopi Formation (TRmu) 

to form the entrenched meander of the Horn, south of 

Hite (plate 1). Like The Rincon, the Horn is capped by 

the Kayenta Formation and Navajo Sandstone. 

Figure 12. Photograph of Horseshoe Bend, Glen Canyon National Recreation Area. Horseshoe Bend is an entrenched 

meander south of Glen Canyon Dam. Near-vertical joints cut through the exposed sandstone and are easily visible in 

the rocks. National Park Service photograph.
21

About 8 km (5 mi) downstream from Glen Canyon 

Dam, the Colorado River carved the horseshoe-shaped 

Horseshoe Bend entrenched meander in Jurassic and 

upper Triassic strata (cover photograph). The butte rises 

300 m (1,000 ft) above the Colorado River. Ledgy slopes 

of the Moenave Formation (JTRmd) at the base of the 

butte are overlain by the Kayenta Formation, and the 

butte is capped by jointed Navajo Sandstone. Hundreds 

of smaller entrenched meanders exist along tributaries 

such as the Escalante and San Juan rivers.

Desert Varnish

The thin, red-to-black coating known as desert varnish 

is found throughout arid regions, such as the Colorado 

Plateau. In Glen Canyon National Recreation Area, this 

surface stain often outlines the large-scale cross-beds in 

the Navajo Sandstone (Jn) and darkens the pale, massive 

sandstones in the Wingate Sandstone (JTRw) (fig. 9). 

The color of the varnish depends on the amount of 

iron relative to manganese. Varnish high in manganese 

appears black; an abundance of iron colors the varnish 

red to orange. Varnishes intermediate in composition 

are usually a shade of brown.

Desert varnish is the product of the interaction between 

microorganisms and rock surfaces. Microorganisms 

oxidize the manganese, which cements clays and other 

particles to rock surfaces. Most rock surfaces in desert 

environments contain these microorganisms, which 

may be able to use both organic and inorganic nutrition 

sources. Sources of manganese and iron originate from 

outside the exposed rock, probably from atmospheric 

dust and surface runoff. Black varnish often occurs 

where water slides over cliffs. 

Because desert varnish takes thousands of years to 

form, it more commonly occurs on erosion-resistant 

strata, such as the Navajo Sandstone cliffs in Glen 

Canyon, rather than on easily eroded surfaces. The 

coating deteriorates under acidic conditions, such as 

acid rain, and may be chemically eroded by lichens. 

Giant Sandstone Pipes and Weathering Pits

Giant sandstone pipes and associated weathering pits in 

Glen Canyon National Recreation Area are also “classic 

geologic sites” (table 3; Anderson et al. 2010). Occurring 

over a 20,000 km2- (7,700 mi2-) area of southeastern 

Utah, these landscape features are primarily in the 

lower part of the Entrada Sandstone (Je), but they also 

occur in the Carmel Formation (Jc) and the Navajo 

Sandstone (Jn) (Netoff 1999; Netoff and Shroba 1993; 

Netoff and Shroba 2001; Huuse et al. 2004; Netoff and 

Chan 2009; Anderson et al. 2010). In the recreation area, 

the features occur on barren exposures of the Entrada 

Sandstone at the north end of Rock Creek Bay, Cookie 

Jar Butte (north shore of Padre Bay), and Warm Creek 

Bay (Netoff and Shroba 2001; Anderson et al. 2010).

The cylindrical sandstone pipes generally form in 

clusters, and their contact with the cross-bedded host 

rock is sharp. The pipes are as much as 75 m (246 ft) 

wide and 100 m (330 ft) high (Netoff 1999). The pipes 

form the core of cone-shaped landforms that vary 

in size from broad domes less than 5 m (16 ft) high 

to narrow, steep-sided cones as high as 70 m (230 ft) 

(Netoff and Shroba 2001). Some of the Entrada pipes 

extend well into the underlying redbeds of the Carmel 

Formation (Wheatley et al. 2014). Small-scale ring 

faults, which are circular or elliptical in plan view, may 

be present at the contact between the pipes and the host 

rock. Local displacement on the ring faults may be as 

much as 5 m (16 ft; Netoff 1999). 

The homogeneous sandstone pipes suggest the 

injection of fluidized sand into the host rock, as do 

the irregular, finger-like projections that also occur 

in the surrounding Entrada Sandstone (fig. 13; Netoff 

1999). Fluidization probably occurred in a watersaturated environment prior to the Entrada Sandstone 

becoming completely lithified. The abundance of these 

sandstone masses along with evidence of liquefaction 

extending to depths exceeding 100 m (330 ft) suggests 

the occurrence of one or more major earthquakes 

on the Colorado Plateau during the Middle Jurassic 

(Phoenix 1958; Davidson 1967; Alvarez et al. 1998; 

Netoff and Shroba 1995; Netoff 1999; Huuse et al. 2004; 

Wheatley et al. 2014). Potential triggering mechanisms 

for such a major seismic event include a possible 

meteor impact approximately 60 million years ago 

that may also be responsible for Upheaval Dome in 

Canyonlands National Park, changes in the regional 

stress field, Jurassic movement along the Mojave-Sonora 

megashear, and explosive volcanism (Netoff 1999; 

Huuse et al. 2004). 

Once exposed by erosion, the conical landforms 

evolved because of differential weathering. Differences 

in pipe material versus the enclosing host rock, clay 

content, type and abundance of microorganisms on 

the rock surface, and distribution of carbonate cement 
22

all contributed to variations in the erosion rates and 

subsequent topographic relief of the cones (Netoff and 

Shroba 2001).

Some of the cones have relatively soft cores, allowing 

weathering pits to form on their summits. The pits range 

from shallow [< 5 m (< 16 ft)] doughnut-shaped pits to 

deep, circular pits as much as 35 m (115 ft) deep and 

37 m (120 ft) wide (fig. 13). The walls of some of these 

deeper pits have been breached, creating an armchairlike shape (Netoff and Shroba 2001). The exceptional 

pits at Cookie Jar Butte are likely among the deepest 

weathering pits on Earth (Netoff et al. 1993; Netoff and 

Shroba 1997; Anderson et al. 2010). Some of the pits 

contain several meters of water, which may remain for 

months or years.

The pits are probably no older than early Pleistocene 

(about 2 million years old), and may be the result of 

several weathering processes including the growth 

of salt crystals from moisture collected in the pits, 

expansion and desiccation of smectite clay, and 

dissolution of calcite cement (Netoff et al. 1994; 

Netoff and Shroba, 1995; Anderson et al. 2010). These 

processes, even today, dislodge and destabilize weakly 

cemented sandstone grains exposed on the surface. 

The relatively flat floors of the deeper, cylindrical 

pits may contain a thin [< 1 m (< 3.3 ft)] mantle of 

sandy sediment (Netoff and Shroba 2001). Questions 

still remain as to how sediment is removed from 

these deep pits. Wind deflation may be one answer. 

Abrasional, depositional, and deflational features in a 

giant sandstone pit in the Navajo Sandstone in Grand 

Staircase-Escalante National Monument suggest 

exceptionally strong winds removed the sediment from 

this pit (Netoff and Chan 2009). Evidence of strong 

winds swirling in some of the Entrada Sandstone pits 

includes pit-floor sand dunes and abrasional features 

such as grooves, flutes, ventifacts, and yardangs 

(streamlined protuberances carved from bedrock by 

wind). Abrasional features indicate two distinct types 

of wind patterns: (1) rotary patterns in which the wind 

rotates around a horizontal axis within the pit, and (2) 

corkscrew-like patterns in which strong vortices rotate 

on a vertical axis (Netoff and Shroba 2001).

Wind deflation certainly can remove loose, dry sand 

from shallow pits, but whether wind can remove 

sand-size grains from the deep, narrow cylindrical 

depressions at Cookie Jar Butte remains debatable 

(Netoff et al. 1993; Anderson et al. 2010). Wind gusts 

as strong as 130 km/h (80 mi/h) occur on Lake Powell, 

and Pleistocene winds may have had an even greater 

velocity as a result of high-pressure gradients between 

the warm, low canyon floors and the ice-capped, high 

Figure 13. Photographs of fluidized injections of sandstone into Entrada Sandstone and a weathering pit that formed 

on a sandstone pipe. This pit is one of many that are clustered near Cookie Jar Butte along Padre Bay. Photographs 

from Anderson et al. (2010, figures 29 and 33).
23

plateaus north of Glen Canyon (Netoff et al. 1993). 

However, some of the deep pits at Cookie Jar Butte lack 

wind scour features on the walls, floors, and bedrock 

surfaces. Some pits have even formed on the leeward 

slopes where wind would not have an impact (Netoff et 

al. 1993).

Recently, Jim Davis of the University of Utah proposed 

a novel idea suggesting that diatoms play a pivotal 

role in the weathering and erosion of potholes (Davis 

2013). Studying the physical-chemical-biological 

relationship in pits near Moab, Utah, Davis found that 

silica concentrations are consistently low in these desert 

geomorphic features and the abundance of benthic 

diatoms is quite high. When the potholes contain 

water, kelp and bacteria etch the sandstone surface and 

diatoms absorb the released silica to form their tests. 

Photosynthetic organisms, such as diatoms, also affect 

the daily pH and oxygen concentrations in the potholes 

and along with fluctuations in water temperature, affect 

the solubility of the surrounding sandstone (Davis 

2013). Diatoms, which have the aerodynamic properties 

of dried leaves, are easily removed from potholes even 

by light winds during dry pothole phases. 

Although the diatom hypothesis requires further 

research, the bio-geologic association may prove to 

be a significant factor in giant pothole formation on 

the Colorado Plateau. Questions remain as to whether 

or not diatoms may directly dissolve sand grains, the 

age of the pits, and the removal of sediment from the 

deep pits in Glen Canyon National Recreation Area. 

The distribution of the pits also presents a conundrum. 

In this vast expanse of exposed friable Navajo and 

Entrada sandstones with similar characteristics, these 

giant weathering pits are clustered in areas that do not 

appear to be exceptionally different from the rest of the 

Colorado Plateau.

Sedimentary Rocks and Sedimentary Rock 

Features

The bedrock in Glen Canyon National Recreation 

Area consists entirely of sedimentary rock, one of the 

three basic rock types (metamorphic and igneous rocks 

are the other two). Sedimentary rocks are classified 

as clastic, chemical, or organic (table 4). Clastic 

sedimentary rocks are the products of weathering, 

erosion, transportation, and deposition of rock or 

fossil fragments called “clasts.” Chemical sedimentary 

rocks form when ions precipitate out of water. Organic 

sedimentary rocks are composed of organic remains, 

such as the decomposition of plants to form peat and 

coal.

Sedimentary rock features in the strata in Glen Canyon 

National Recreation Area help define the various 

depositional environments that occupied southeastern 

Utah during the Mesozoic and Paleozoic Eras (see the 

“Geologic History” chapter). These features commonly 

form from both marine and terrestrial processes and 

can be divided into three general categories: (1) marine 

and nearshore marine features, (2) fluvial and floodplain 

features, and (3) eolian and associated features (table 

5). Fossils are important resources in many sedimentary 

rocks within the recreation area. They are further 

described in the “Paleontological Resources” section. 

Marine and Nearshore Marine Features

Beds of limestone, sandstone, and mudstone 

containing fossils of marine organisms are the primary 

sedimentary features that characterize marine 

depositional environments (table 5). Most of the marine 

limestone in Glen Canyon National Recreation Area 

is found in Paleozoic Era strata. Contorted beds of 

the upper part of the Middle Pennsylvanian Paradox 

Formation (PNp) are exposed in the deepest parts of 

Cataract and San Juan River canyons. The formation 

contains cyclic layers of black organic shale, siltstone, 

gypsum, lime mudstone, wackestone, packstone, ooid 

grainstone, and algal boundstone. Fossils include a 

variety of marine invertebrates including crinoids, 

bryozoans, brachiopods, fusulinids, corals, foraminifers, 

conodonts, and fish fragments.

Exposed in the northern part of the park along the 

Colorado River and into neighboring Canyonlands 

National Park, the Late Pennsylvanian Honaker Trail 

Formation (PNht), which averages 170 m (550 ft) thick 

in the park, contains fossils of marine invertebrates 

including foraminifera, bryozoans, gastropods, crinoids, 

and conodonts (Ritter et al. 2002; Tweet et al. 2009).

Limestone in the Halgaito Formation (PPNhg) contains 

fossils of sharks and fish near Cedar Point in Glen 

Canyon National Recreation Area and in John’s Canyon 

just outside of the park boundaries (table 7; Tweet et 

al. 2009). Fossils of marine invertebrates occur in both 

the Halgaito and Elephant Canyon (PPNe) formations 

and include foraminifera, corals, crinoids, conodonts, 

bryozoans, brachiopods, cephalopods, trilobites, and 
24

echinoderms (Tweet et al. 2009). Like the Honaker Trail 

Formation, the Halgaito-Elephant Canyon interval is 

restricted to the northern portion of the recreation area 

and the San Juan Arm (Anderson et al. 2010). The two 

units are age-equivalent and interfinger (fig. 14).

Cyclic interbeds of fossiliferous limestone, siltstone, 

sandstone, black organic shale, dolomite, and/or 

gypsum in the Paradox (PNp), Honaker Trail (PNht), 

Halgaito (PPNhg), and Elephant Canyon (PPNe) 

formations characterize marginal marine or nearshore 

depositional environments and represent episodes 

of sea level rise (transgression) followed by sea level 

lowering (regression) (Langford and Chan 1987; 

Langford et al. 2007; Tweet et al. 2009; Anderson et al. 

2010). The cycles in the Paradox Formation (PNp) that 

are exposed throughout the Colorado Plateau provide 

a textbook example of fluctuating sea levels during 

the Middle Pennsylvanian in western North America 

(Wengerd 1962; Rueger 1996). The Halgaito-Elephant 

Canyon interval averages 75 m (250 ft) thick in the park, 

Table 4. Sedimentary rock classification and characteristics.

Sedimentary 

Rock Type Rock Name Texture Depositional Environment

Inorganic Clastic*

Conglomerate (rounded clasts) Clast size: >2 mm (0 08 in). Ranges from higher energy (swift river

currents; strong winds) for larger grain 

sizes to lower energy (floodplains, 

lagoons, lakes) for smaller grain sizes

Breccia (angular clasts)

Sandstone Clast size: 1/16–2 mm (0 0025–0 08 in)

Siltstone Clast size: 1/256–1/16 mm (0 00015–0 0025 in)

Claystone Clast size: <1/256 mm (0 00015 in)

Carbonate Clastic**

Fossiliferous Limestone Generic name for carbonate rock containing 

fossils Primarily marine

Crystalline Crystal supported; no fossil fragments, carbonate 

grains, or carbonate mud

No depositional features can be 

recognized

Boundstone Composed entirely of fossils, fossil fragments, or 

carbonate mud fragments cemented together

Higher energy setting Bound together 

during deposition (e g , reefs)

Grainstone Grain (i e , fossil fragments) supported with no 

carbonate mud

Original components bound together 

following deposition; depositional 

settings range from higher energy 

(grainstone) to lower energy (mudstone)

Packstone Grain (i e , fossil fragments) supported with some 

carbonate mud

Wackestone Carbonate mud supported with more than 10% 

grains and less than 90% carbonate mud

Mudstone Carbonate mud supported with less than 10% 

grains and more than 90% carbonate mud

Chemical

Limestone (Carbonate Mud)

Generic name Formed by the precipitation of 

calcium (Ca) and carbonate (CO3

2-) ions from 

water

Freshwater (lakes) or marine 

environments

Travertine Precipitation of calcium (Ca) and carbonate (CO3

2-) 

ions from freshwater Terrestrial springs

Dolomite Precipitation of calcium (Ca), magnesium (Mg), 

and carbonate (CO3

2-) ions from water

Post-depositional alteration of 

limestone by Mg-rich ground-water or 

direct precipitation in shallow marine 

environments

Evaporites (e g , gypsum).. Precipitation of salts to form evaporite minerals Hot, dry environme

Oolite 

Precipitation of calcium carbonate in thin spherical 

layers around an original particle (i e , fossil 

fragment)

Shallow marine environment; particles 

are rolled back and forth by the 

constant motion of tides or waves

Organic Coal Peat (partly decomposed plant matter) is buried, 

heated, and altered over time Lagoon, swamp, marsh

* Claystones and siltstones can also be called “mudstone,” or if they break into thin layers, “shale.

**Carbonate classification is based on Dunham’s textural classification scheme (Dunham 1962)

Refer to the Map Unit Properties Tables (in pocket) and glca_geology.pdf (in GRI GIS data) to identify formations comprised of these rock types in

Glen Canyon National Recreation Area
25

Table 5. Sedimentary rock features identified in Glen Canyon National Recreation Area.

Feature Type Feature Process/Depositional 

Environment Formation (map symbol)

Eolian and 

Associated 

Features

Well-sorted, frosted sandstone grains

Eolian (wind) processes; grains colliding 

against each other results in a translucent 

(frosted) coating

Entrada Sandstone (Je), 

Page Sandstone (Jpj, Jpt),

Navajo Sandstone (Jn),

Wingate Sandstone (JTRw)

Local high-angle cross-bedding

Eolian processes that produce local sand 

dunes in a nearshore, coastal environment, 

which may contain sabkhas

Straight Cliffs Formation (Ksj),

Romana Sandstone (Jr),

Coconino Sandstone (Pco),

Organ Rock Formation (Po)

Extensive high-angle cross-bedding Eolian processes that form vast Sahara-like 

deserts (ergs) with migrating sand dunes

Entrada Sandstone (Je),

Page Sandstone (Jpj, Jpt),

Navajo Sandstone (Jn),

Wingate Sandstone (JTRw),

White Rim Sandstone (Pwr),

Cedar Mesa Sandstone (Pcm)

Limestone lenses with algae, ripple marks, 

and mudcracks Oases or lakes in interdune areas of the erg Navajo Sandstone (Jn)

Fluvial and 

Floodplain 

Features

Trough cross-bedding Sandstones deposited in fluvial channels

Kayenta Formation (Jk),

Chinle Formation (TRcc, TRcs),

Organ Rock Formation (Po)

Mottled red and gray clay layers; root 

zones

Paleosol (fossil soil) development; 

preserved on floodplains Chinle Formation (TRcc, TRcop, TRcmn)

Combination of interbedded or fining 

upward sequences of conglomerate, 

sandstone, siltstone, and mudstone; 

reddish-brown color; ripple laminations; 

mudcracks; and/or small-scale cross-beds

Fluvial processes; floodplain and overbank 

deposits; paleosol development

Straight Cliffs Formation (Ksl, Ksj),

Dakota Formation (lower) (Kd),

Morrison Formation (Jm),

Kayenta Formation (Jk),

Moenave Formation (JTRmd),

Chinle Formation (TRcc, TRcms, TRcmn), 

Moenkopi Formation (TRm),

Organ Rock Formation (Po),

Cedar Mesa Sandstone (Pcm)

Dinosaur and reptile bones and/or tracks Terrestrial animal remains

Morrison Formation (Jm),

Navajo Sandstone (Jn),

Kayenta Formation (Jk),

Chinle Formation (TRc),

Moenkopi Formation (TRm)

Petrified wood Wood fragments transported by fluvial 

processes Chinle Formation (TRcop)

Coal beds Deposition under anaerobic conditions 

followed by burial in coastal lagoons

Straight Cliffs Formation (Ksl, Ksj),

Dakota Formation (middle) (Kd)

Marine and 

Nearshore 

Marine Features

Planar beds of calcareous sandy siltstone 

with local gypsum

Tidal flat, nearshore, shallow marine 

deposition and evaporite deposits 

(gypsum)

Romana Sandstone (Jr),

Carmel Formation (Jcu)

Cyclic interbeds of fossiliferous limestone, 

cherty limestone, dolomite, siltstone, 

organic shale, and/or gypsum

Alternating nearshore, marine 

environments caused by a fluctuating sea 

level in an arid climate

Halgaito Formation (PPNhg),

Elephant Canyon Formation (PPNe),

Honaker Trail Formation (PNht),

Paradox Formation (PNp)

Shallow marine invertebrate fossils and 

burrows Beach and shallow marine Straight Cliffs Formation (Ksl)

Marine invertebrate fossils in sandstone or 

mudstone Marine environments Tropic Shale (Kt),Dakota Formation (upper) (Kd)
26

and the cyclic stratigraphic relationships suggest that 

transgressions occurred every 300,000 to 400,000 years 

(Langford and Chan 1987; Tweet et al. 2009; Anderson 

et al. 2010).

The layers of calcareous sandstone, siltstone, local 

gypsum, and limestone found in the Middle Jurassic 

Carmel Formation (Jcu) and Upper Jurassic Romana 

Sandstone (Jr), which bracket the eolian sand dunes 

of the Entrada Sandstone (Je), document nearshore, 

tidal flat, or shallow marine depositional environments 

(table 5). Good exposures of the Carmel Formation 

occur along Bullfrog Bay, near Dangling Rope Marina, 

and in upper Rock Creek. Romana Sandstone strata are 

exposed south of the Circle Cliffs uplift (Anderson et al. 

2010).

In the Glen Canyon region, sandstone and mudstone, 

rather than limestone, characterize marine and 

nearshore marine environments during the Late 

Cretaceous (table 5). Oysters and clams, indicative of 

marine to brackish environments, occupy a 5–50 m- 

(20–170 ft-) thick band in the upper part of the Dakota 

Formation (Kd) between Wahweap Bay and Fiftymile 

Mountain and near Last Chance Bay (Anderson 

et al. 2010). The Dakota Formation is an extensive 

heterogeneous rock unit which formed in a variety 

of depositional environments. On the Colorado 

Plateau, the Dakota Formation has been divided 

into three informal members: (1) a lower member 

reflecting fluvial channels, (2) a middle member 

representing coastal plain environments, and (3) an 

upper member deposited in coastal, transgressive 

marine environments. Plant material deposited 

in anoxic coastal lagoons became coal beds in the 

Dakota (Kd) and Straight Cliffs (Ks) formations.

Marine fossils are also found in the overlying, 

poorly exposed Tropic Shale (Kt). The Tropic 

Shale represents the maximum transgression of 

the Western Interior Seaway into the area (see the 

“Geologic History” chapter).

The thick Straight Cliffs Formation (Ks) has been 

divided into four members, and the sedimentary 

features in these members represent fluctuating 

Late Cretaceous sea levels (Peterson 1969). In Glen 

Canyon National Recreation Area, the lower two 

members, the basal Tibbet Canyon Member and 

overlying Smoky Hollow Member, are mapped 

as one unit (Ksl). The cliff-forming sandstone of 

the Tibbet Canyon Member contains pelecypods, 

gastropods, cephalopods, shark teeth and trace fossils 

from beach and shallow marine environments (table 

5; Tweet et al. 2009). The Tibbet Canyon Member 

transitions into the Smoky Hollow Member, a 

heterogeneous unit with features reflecting fluvial, 

floodplain, lagoonal, and marsh settings. Coastal 

features and marine fossils mark a rise in sea level and 

a marine transgression in the slope- and ledge-forming 

John Henry Member (Ksj), but only the lower part of 

this rock unit is present within Glen Canyon National 

Recreation Area (Tweet et al. 2009). The uppermost 

member, the cliff- and bench-forming Drip Tank 

Member (Ksd), is present in the westernmost part of 

the enclosed posters (in pocket), but it is outside the 

recreation area. 

Fluvial and Floodplain Features

Sedimentary features in this category represent 

processes associated with fluvial systems (table 5). Grain 

size is an indicator of depositional environment. For 

example, lenses of conglomerate in the upper part of 

the Organ Rock Formation (Po) represent high energy 

stream channel deposits, while trough-shaped crossbedded sandstone and asymmetrical ripple marks, such 

Figure 14. Schematic illustrating the Interfingering of the 

Elephant Canyon and the Halgaito Formations, Glen Canyon 

National Recreation Area. Yellow and red colors represent 

clastic, primarily terrestrial rocks; blue colors are dominantly 

carbonate, marine rocks. Schematic from Anderson et al. 

(2010, figure 10).
27

as those in the Lower Triassic Moenkopi Formation 

(TRm) and Upper Triassic Chinle Formation (TRc), 

characterize lower velocity flow regimes. Because 

higher channel velocities are required to transport 

larger clasts compared to finer grained sand and silt 

grain size becomes an important indicator of the energy 

level during deposition.

Fluvial and floodplain ecosystems dominated the 

region in the Triassic Period (see the “Geologic 

History” chapter). Petrified wood, dinosaur tracks (see 

“Paleontological Resources” section), and mudcracks 

(fig. 15) that formed when overbank floodwaters 

evaporated are common sedimentary features in the 

Early–Middle Triassic Moenkopi Formation (Anderson 

et al. 2010). Periodic flooding deposited silt and clay on 

the floodplain, and mottled, reddish-brown and gray 

layers record the development of paleosols (old soils) 

(table 5). Mudcracks are not unique to the Moenkopi 

Formation, but those found in Red Canyon offer a rare 

view of mudcracks shown in profile (fig. 15) and are one 

of the “classic geologic sites” of Anderson et al. (2010). 

The v-shaped cracks formed in red siltstone, and they 

were filled by light-gray sandstone, making them easy to 

identify.

The Moenkopi Formation in Glen Canyon National 

Recreation Area is not as thick as exposures to the 

northeast and west where it is 

subdivided into several members 

(Blakey 1974; Anderson et al. 2010; 

Billingsley and Priest 2010; Doelling 

et al. 2010; Morris et al. 2010). In 

the park, the unit ranges from 80 

to 150 m (270–500 ft) thick and 

has been subdivided into a basal 

Hoskinnini Member (TRmh) and 

upper and lower members (TRmu, 

TRml), which have similar lithology.

Sedimentary features in the six 

members of the Upper Triassic 

Chinle Formation include crossbedding, ripple marks, thin 

coal or shale beds, uraniumbearing logs, paleosols, mottled 

limestone, smectitic clay layers, 

and dinosaur bones and tracks, 

which characterize a complex 

interlayering of fluvial, lacustrine, 

floodplain, and eolian deposits 

(table 5). Conglomerate and sandstone of the basal 

Shinarump Conglomerate Member (TRcs) fill channels 

and paleovalleys incised into the underlying Moenkopi 

Formation (Anderson et al. 2010). 

Cross-bedded sandstone interbedded with reddishbrown siltstone and shale in the Early Jurassic Kayenta 

Formation (Jk) represent shifting freshwater braided 

and meandering streams that flowed across the 

area between 197 million and 190 million years ago 

(Colbert 1974; Lucas et al. 2005; Tweet et al. 2009). 

The formation is exposed in the Good Hope Bay area, 

between The Rincon and a few miles south of the 

Escalante-Colorado River junction, and in the western 

San Juan Arm (Anderson et al. 2010). A 55–68 m- 

(180–223 ft-) thick basal Springdale Sandstone Member 

(Jks) is mapped in the Lees Ferry area. The upper part 

of the formation contains more sandstone than siltstone 

and intertongues with the overlying Navajo Sandstone, 

documenting a time when the Navajo Sandstone sand 

dunes advanced into the area and smothered the rivers 

of the Kayenta Formation (Harshbarger et al. 1957; 

Kocurek and Dott 1983).

Fluvial systems are also represented by the 

conglomerate, sandstone, sandy mudstone, and 

shale in the basal part of the Dakota Formation (Kd). 

Figure 15. Photograph of cross-section of mudcracks, Red Canyon, Glen 

Canyon National Recreation Area. These mudcracks formed in the Moenkopi 

Formation. Light-colored silt filled the cracks after they formed in the reddishbrown shale. Photograph from Anderson et al. (2010, figure 23).
28

Conglomerates and sandstone were deposited in 

channels while the finer-grained sediments (mudstone 

and shale) were deposited on the floodplain. The upper 

sandstone and marine fossils in the upper Dakota 

Formation reflect a transition from this fluvial landscape 

to coastal and marine environments as the Western 

Interior Seaway advanced into the region.

The interbedded sandstone, siltstone, carbonaceous 

mudstone, and coal in the ledge- and slope-forming 

Smoky Hollow Member (Ksl) of the Upper Cretaceous 

Straight Cliffs Formation record the reintroduction of 

fluvial and floodplain environments to the region. The 

member is 7–40 m (24–132 ft) thick and was deposited 

about 91 million years ago (Kirkland and Eaton 2002).

Eolian and Associated Features

As they do today, eolian processes in the past 

transported available sand grains and shaped them into 

sand dunes with gentle windward slopes and high-angle 

slopes (foreset beds) approaching the angle of repose 

on the dune slipface (fig. 16). Ancient sand dunes with 

high-angle cross-beds of well-sorted sand grains are 

preserved in a variety of formations in Glen Canyon 

National Recreation Area (table 5). High velocity winds 

created a natural sandblasting affect that “frosted” 

the sand grains with a translucent coating. Today, this 

process may be experienced by travelers crossing the 

deserts of the southwest during a wind storm. Vehicle 

windshields become pitted and frosted due to the 

impact of the sand grains on glass.

Localized high-angle cross-bedded sandstone 

preserved in Permian, Jurassic, and Cretaceous 

strata represents ancient coastal dune fields (table 

5). Excellent exposures of coastal sand dunes in the 

Early Permian Period Cedar Mesa Sandstone (Pcm), 

Organ Rock Formation (Po), and overlying White Rim 

Sandstone (Pwr) occur in the northern part and the 

San Juan section of the recreation area (Anderson et al. 

2010). The dunes that compose the 210–425 m- (700–

1,400 ft-) thick Cedar Mesa Sandstone are separated 

by erosion surfaces that may represent episodes of 

marine transgressions (sea level rise) which occurred 

on the order of every 300,000 to 400,000 years, similar 

to the timing of marine transgressions in the HalgaitoElephant Canyon interval (Langford and Chan 1987; 

Langford et al. 2007; Tweet et al. 2009). 

The presence of horizontally bedded sandstone, algal 

limestone, and gypsum indicate that these sand dunes 

were part of a coastal environment that included eolian 

dunes and sabkhas. Sabkhas are relatively flat surfaces 

that form when sea water evaporates. Early Permian 

marine environments north of Glen Canyon National 

Recreation Area support this coastal interpretation 

(Anderson et al. 2010; Baars 2010; Huntoon et al. 2010). 

In the Late Triassic and Jurassic Periods, vast inland 

dune fields (ergs) similar to those in today’s Sahara 

Desert swept across the Colorado Plateau (see the 

“Geologic History” chapter). These extensive dune 

fields are preserved in the cross-bedded sandstone that 

forms the massive cliffs and rounded domes of Wingate 

(JTRw), Navajo (Jn), and Entrada (Je) sandstones (fig. 

17).

Figure 16. Schematic cross-section of a sand dune. Foreset beds form on the slipface and are preserved in the eolian 

deposits exposed in Glen Canyon National Recreation Area. Graphic by Trista Thornberry-Ehrlich (Colorado State 

University), modified from Ahlbrandt and Fryberger (1982, figure 3).
29

The Navajo Sandstone is one of the largest preserved 

eolian systems in the stratigraphic record, and 

represents the most widespread eolian deposit in North 

America (Blakey 1994; Peterson 1994). In the Navajo 

Sandstone, cross-bed sets are up to 23 m (75 ft) thick. 

Weathering has etched out the cross-beds, and they are 

often outlined by desert varnish (Anderson et al. 2010). 

Excellent exposures of cross-bedded Navajo Sandstone 

occur across the Colorado Plateau and are preserved in 

a number of national parks including Navajo National 

Monument (see GRI report by Graham 2007), Capitol 

Reef National Park (see GRI report by Graham 2006a; 

Morris et al. 2010), Arches National Park (see GRI 

report by Graham 2004; Doelling 2010), and Zion 

National Park (see GRI report by Graham 2006b; Biek 

et al. 2010).

Unusual Sedimentary Rock Features

Unusual processes often produce unusual features. 

Oasis deposits, Moqui marbles, soft sediment 

deformation, and tafoni are some of the unusual 

features preserved in Glen Canyon National Recreation 

Area.

Oasis Deposits

Thinly bedded, 1.5–3 m- (5–10 ft-) thick limestone in 

the Navajo Sandstone (Jn) represents oases that formed 

between dunes within a vast Jurassic desert, similar to 

the vegetated oases in the Sahara (table 5). Sedimentary 

features in the limestone include oscillation ripples 

(formed by water moving back and forth), mudcracks, 

fossil plants, possible algal layers (stromatolites), and 

dinosaur tracks (fig. 18; Stokes 1991; Anderson et al. 

2010; Santucci and Kirkland 2010). Flood velocities can 

erode river beds, ripping up pieces of the underlying 

mud and shale and transporting them downstream. 

The oasis deposits contain rip-up clasts of underlying 

interdune sediments within overlying stromatolites 

(algal laminations), indicating that large quantities of 

water sometimes inundated the Navajo desert (Loope et 

al. 2004; Irmis 2005). 

Figure 17. Photograph of cross-bedding in Jurassic Navajo Sandstone sand dunes. The “petrified” foreset beds on the 

slipface of these ancient dunes capture the shifting nature of modern sand dunes. National Park Service photograph 

by Bob Moffitt, taken in 2013, available online: http://www.nps.gov/glca/learn/photosmultimedia/photogallery.htm

(accessed 11 September 2015).
30

The Jurassic oases were quite extraordinary and 

represent enigmatic sedimentary depositional 

environments that contrasted sharply with the 

surrounding desert. They are included in the “classic 

geologic sites” of Anderson et al. (2010) and can be 

found along the main channel of Lake Powell and in 

Forgotten, Moqui, Annies, Slickrock, Iceberg, and 

Escalante canyons.

Freshwater lakes or ponds also formed in these vast 

deserts (Gilland 1979; Anderson et al. 2010). For lakes 

to develop, shallow groundwater had to persist for 

extended periods of time, perhaps for thousands of 

years (Stokes 1991; Anderson et al. 2010). Lake deposits 

are preserved in Canyonlands National Park (Gilland 

1979).

Moqui Marbles and the Mars Connection

Moqui marbles, also referred to as “Navajo berries,” 

are nearly spherical concretions of friable (loosely 

cemented) sandstone surrounded by an ironstone shell 

of densely cemented hematite (Fe2O3) (Doelling 1968, 

1975; Chan et al. 2004; Downs and Wronkiewicz 2007; 

Anderson et al. 2010). They are common in the Navajo 

Sandstone (Jn) throughout southern Utah, and are 

found eroding from the spectacular white cliffs in Zion 

National Park and Grand Staircase-Escalante National 

Monument (see GRI report by Graham 2006b). The 

concretions, which range from pea size to as much as 

10 cm (4 in) in diameter, are more resistant to erosion 

than the surrounding sandstone, thus they stand out on 

bedding planes or weather out to form aprons of loose 

concretions at the base of an outcrop (fig. 19). Moqui 

marbles are generously scattered on the surface of the 

Navajo Sandstone along the popular Horseshoe Bend 

trail, downstream from Glen Canyon Dam, and are 

considered to be one of the “classic geologic sites” in 

Anderson et al. (2010).

To form, the berries require a porous and permeable 

host rock, groundwater flow, and a chemical reaction 

between groundwater and iron-rich fluids (Chan et al. 

2004). The Navajo Sandstone is one of the more porous 

and permeable formations in southern Utah. It serves 

as both a reservoir for hydrocarbons and groundwater. 

Meteoric groundwater and weathering processes 

disseminate iron films in the sandstone, resulting in 

the sandstone’s familiar pinkish to orange-red color. 

Reducing fluids, such as hydrocarbons or acidic water, 

mobilize the iron-oxide films, and when these iron-rich 

fluids interact with oxygenated groundwater, hematite 

precipitates, usually as spherical balls (Chan and Parry 

2002; Chan et al. 2004; Anderson et al. 2010). The 

lack of central nuclei in these Moqui marbles suggests 

that hematite precipitation and the spacing between 

each marble may be controlled by several factors such 

as characteristics of the sandstone, fluid chemistry, 

oxidation potential, pH, flow paths, timing, and possibly 

the presence of bacteria (Chan et al. 2004).

Figure 18. Photographs of features typically found in the 

“oasis” deposits in the Navajo Sandstone. (A) Mudcracks 

(desiccation cracks) formed in oasis limestone above a 

bed containing ripple marks; Forgotten Canyon. (B) Algal 

laminae within limestone oasis beds; Moqui Canyon. 

Photographs from Anderson et al. (2010, figure 25).
31

Hematite precipitation may form a variety of unusual 

shapes in addition to spherical concretions, such as 

bulbous nodules, pipes, and sheets (Chan et al. 2004). 

In Glen Canyon National Recreation Area, thin sheets 

of iron have precipitated along the surface of Navajo 

cross-beds and in highly contorted beds, such as those 

on Antelope Island (fig. 19). 

Iron concretions are not unique to the Navajo 

Sandstone. They have been documented from a variety 

of rock types and geologic settings. However, the 

Moqui marbles in the Navajo Sandstone, including 

those identified in Glen Canyon National Recreation 

Area, bear a strong resemblance to iron concretions 

found on Mars by NASA’s twin Spirit and Opportunity

rovers. Both Moqui and Martian concretions are 

spherical, composed of hematite, and form loose, 

weathered accumulations. Merely the presence of 

hematite suggests that large volumes of subsurface 

fluids flowed through porous rock (Chan et al. 2004). 

Research continues into the comparison between the 

concretions, the source of iron, and the driving force 

of fluid flow, but for now, the Moqui marbles provide a 

Figure 19. Unusual sedimentary features in the Navajo 

and Entrada sandstones, Glen Canyon National 

Recreation Area. (A) Moqui marbles in the Navajo 

Sandstone, east shore of the main channel west of 

Crossing of the Fathers. (B) Ironstone sheets along 

Navajo Sandstone bedding planes, west shore of 

Bullfrog Marina. (C) Soft-sediment deformation in 

Navajo Sandstone, south side of Antelope Island. (D) 

Tafoni (holes) in Entrada Sandstone, Dry Rock Creek 

Canyon. (E) Small-displacement faults within the Entrada 

Sandstone, Last Chance Bay. The faults do not penetrate 

the stratigraphic layers above and below the deformed 

bed. Photographs from Anderson et al. (2010, figures 27 

and 31).
32

significant terrestrial analogue for the Martian marbles 

(Chan et al. 2004; Downs and Wronkiewicz 2007).

Soft-sediment Deformation in Navajo Sandstone

When sediments are still unconsolidated, they can be 

deformed by gravity- or seismic-induced movements. 

This type of deformation is known as “soft-sediment” 

deformation. The resulting slides or slumps can 

produce faults, folds, and breccias that are unrelated 

to any tectonic deformation process. Soft-sediment 

deformation usually bears no relation to larger 

structures or regional tectonic patterns. The faults and 

folds produced by soft-sediment deformation are small 

scale, and the deformed beds are often truncated by a 

bedding plane (fig. 19).

In Glen Canyon National Recreation Area, spectacular 

soft-sediment deformation occurs in the Navajo 

Sandstone (Jn). On Antelope Island, Navajo sandstone 

beds have been contorted and deformed into tight, 

recumbent (overturned) folds (fig. 19). Because the 

folds tend to trap fluids, ironstone has formed in sheets 

along the bedding surfaces (Anderson et al. 2010).

Tafoni

Tafoni, one of the “classic geologic sites” of Anderson et 

al. (2010), are small holes that are found in the Entrada 

(Je), Page (Jp), Navajo (Jn), Wingate (JTRw), White 

Rim (Pwr), and Cedar Mesa (Pcm) sandstones (fig. 19). 

Tafoni forms when groundwater weakens the mineral 

cement between sand grains, usually around small 

variations in the cement, and weathering removes the 

loose grains, creating holes. Water accumulates in the 

holes, which shelter the water from evaporation. The 

water further weakens the rock cement and the holes 

grow (Anderson et al. 2010). 

A hardened crust may form around tafoni, a process 

known as “case hardening.” The dry, arid climate of 

the southwestern US draws groundwater in porous 

sandstones toward the surface of the rock. When fresh 

water evaporates, mineral cement is left behind that 

hardens the rock “case.”

Paleontological Resources

Paleontological resources (fossils) are any evidence 

of life preserved in a geologic context (Santucci et al. 

2009). All fossils are nonrenewable, and collecting 

is prohibited in the recreation area. Body fossils are 

any remains of the actual organism such as bones, 

teeth, shells, or leaves. Trace fossils are evidence of 

biological activity; examples include burrows, tracks, or 

coprolites (fossil dung). Fossils in NPS areas occur in 

rocks or unconsolidated deposits, museum collections, 

and cultural contexts such as building stones or 

archeological resources. As of June 2016, 262 parks, 

including Glen Canyon National Recreation Area, had 

documented paleontological resources in at least one 

of these contexts. The NPS Fossils and Paleontology 

website provides more information

http://go.nps.gov/fossils_and_paleo; accessed 20 June 

2016). 

Fossils play a significant role in determining the 

environment and climate at the time they were 

deposited, and greatly contribute to understanding 

the geologic history at Glen Canyon National 

Recreation Area. The recreation area contains a 

myriad of paleontological resources and preserves 

one of the most complete sections of Mesozoic strata 

in the world (National Park Service 2014a). Fossils 

may potentially be found in every formation present 

within the recreation area (table 6). Kirkland et al. 

(2010) completed a paleontological resource inventory 

and monitoring report for Glen Canyon Recreation 

Area. During their field investigation, they discovered 

undocumented tracksites and other fossil localities.

Fossils discovered in Glen Canyon Recreation Area are 

housed in several locations, including the recreation 

area, the Western Archeological and Conservation 

Center (WACC), museums, and academic institutions 

(Tweet et al. 2009). The recreation area’s collections 

include the Kayenta Formation tracks discovered in 

Explorer’s Canyon. The WACC natural history catalog 

contains 39,461 paleontological objects arranged under 

1,668 catalog numbers (Tweet et al. 2009). Almost all of 

these came from packrat middens or various caves in 

the recreation area.

The fossils summarized in this GRI report (tables 6, 7, 

8, 9) only reflect those found within the park or in the 

immediate vicinity of the park. However, a complete list 

of fossils found on the Colorado Plateau and references 

associated with those discoveries may be found in Tweet 

et al. (2009). Currently, the recreation area has about 

350 documented sites, although some lack sufficient 

coordinate data (John Spence, written communication, 

9 December 2015). The Utah Geological Survey 

maintains an unpublished database of fossil localities 
33

in Glen Canyon National Recreation Area (Tweet 

et al. 2009). Servicewide summaries of types of 

paleontological resources also include information on 

the scope and significance of fossil vertebrate trackways 

(Santucci et al. 2006), Mesozoic mammals (Tweet and 

Santucci 2015), packrat middens (Tweet et al. 2012), 

coprolites, and bromalites (urine deposits; Hunt et al. 

2012) from Glen Canyon National Recreation Area. 

Resource management issues associated with Glen 

Canyon paleontological resources are described in the 

“Paleontological Resource Inventory, Monitoring, and 

Protection” section.

Paleozoic Era Fossils: Pennsylvanian and Permian 

Periods

Marine and Nearshore Environments

In general, fossils from Paleozoic Era strata in Glen 

Canyon National Recreation Area represent a transition 

from marine to nearshore, coastal conditions (table 

7). Fauna that lived in normal, well-circulated marine 

environments populate the Honaker Trail Formation 

(PHht), and these are joined by fossils common to 

nearshore marine environments in the overlying Late 

Pennsylvanian and Early Permian Halgaito (PPNhgu, 

PPNhgl) and Elephant Canyon Formations (PPNe; table 

7). The rare “sail back” Platyhystrix, an extinct early 

amphibian, was discovered in a conglomeratic stream 

channel in the Halgaito Formation (Sumida et al. 1999; 

Kirkland et al. 2010; Santucci and Kirkland 2010).

The Cedar Mesa Sandstone (Pcm) contains three 

published tracksites in Glen Canyon National 

Recreation Area: Dirty Devil, Grand Gulch, and Steer 

Gulch (Tweet et al. 2009). The Dirty Devil tracksite was 

the first Permian tracksite known from the Glen Canyon 

area and documented the skink Anomalopus attacking 

its prey, the beetle Stenichus (Lockley and Madsen 1993; 

Kirkland et al. 2010). The tracks at the other two Cedar 

Mesa Sandstone sites were mostly made by synapsids 

(mammal-like reptiles) and tracks that are similar to 

Anomalopus and tetrapod fossil track genus Chelichnus. 

Table 6. Relative distribution of tracks and bones found in the stratigraphic units along the shoreline of Lake Powell, Glen 

Canyon National Recreation Area. 

Period and Epoch Geologic Unit (map symbol) Distribution of 

Tracks

Distribution of 

Bones

Middle Jurassic Carmel Formation: Paria River and Winsor members (Jcu, Jcw, Jcp) Rare Rare

Middle Jurassic Page Sandstone (Jpj, Jpt) Present Present

Lower Jurassic Glen Canyon Group: Navajo Sandstone (Jn, Jnl) Present Rare

Lower Jurassic Glen Canyon Group: Kayenta Formation (Jk, Jks) Present Present

Lower Jurassic–Upper 

Triassic Glen Canyon Group: Wingate Sandstone (JTRw) Present Rare

Upper Triassic Chinle Formation: Church Rock Member (TRcc, TRcu) Common Common

Upper Triassic Chinle Formation: Owl Rock and Petrified Forest members

(TRcop, TRcu) Present Common

Upper Triassic Chinle Formation: Moss Back Member (TRcu, TRcms) Present Common

Upper Triassic Chinle Formation: Monitor Butte Member (TRcmn) Present Common

Upper Triassic Chinle Formation: Shinarump Conglomerate Member (TRcs) Present Present

Lower Triassic Moenkopi Formation: Upper member (TRmu) Rare Rare

Lower Triassic Moenkopi Formation: Hoskinnini Sandstone Member (TRmh) Rare Rare

Lower Permian Cutler Group: White Rim Sandstone (P, Pc, Pwr) Rare Rare

Lower Permian Cutler Group: Organ Rock Formation (Pc, Po) Present Present

Lower Permian Cutler Group: Cedar Mesa Sandstone (P, Pc, Pcm) Rare Rare

Lower Permian–Upper 

Pennsylvanian

Cutler Group: Lower Cutler beds/Halgaito Formation

(Pc, PPNcl, PPNhgu, PPNhgl) Present Present

Upper Pennsylvanian Hermosa Group: Honaker Trail Formation (PNht, PNhtu, PNhtl) Rare Rare

Information from Kirkland et al. (2010, figure 1

Colors in Period and Epoch column correspond to US Geological Survey colors for geologic time periods. Colors in distribution columns correspond to

relative abundance of fossil tracks or bones: Rare (yellow), Present (orange), or Common (green)
34

Lizard-like tracks are also known from Oljeto Wash 

(Lockley et al. 1998). 

Discovered in 1973, the Dirty Devil tracksite consists 

of a large sandstone block tilted vertically. In 1973, the 

average annual lake level was 1,104.94 m (3,625.13 ft) 

above sea level, but from 1974 to 2003, lake level was 

higher and the tracksite was submerged below the 

surface of Lake Powell except for one year, 1992. An 

unsuccessful attempt was made to find the tracksite 

in 1992, but silt had accumulated in the lower reaches 

of the Dirty Devil River and the site could no longer 

be reached by either boat or from the precipitous 

canyon walls (Lockley and Madsen 1993). It appeared 

that the tracksite would only exist in photographs 

and replicas of the tracks taken in 1973. Since 2003, 

however, lake levels have often been lower than the 

1973 mark, exposing the Dirty Devil tracksite (Lake 

Powell Water Database 2016; Vincent Santucci, NPS 

Geologic Resources Division, paleontologist, written 

communication 20 December 2015). Global climate 

change models predict increased temperatures and 

decreased precipitation for the region, which may result 

in lower lake levels and exposure of other previously 

submerged fossil sites. 

Outside of the park, nonmarine and marine fossils have 

been found near the top of the Cedar Mesa Sandstone. 

These fossils include leaf impressions, root casts, 

vertebrate tracks, and invertebrate marine fossils such as 

stromatolites, algae, fusulinids, bryozoans, brachiopods, 

gastropods, and crinoids. This fossil association has 

been interpreted to represent tidal inlets or estuaries 

(Loope 1984; Tweet et al. 2009). 

Mesozoic Era Fossils: Triassic Period

Terrestrial Trace Fossils and Plants

Terrestrial tracksites dominate the fossil resources in 

the Triassic and Jurassic Periods (table 8). The Early–

Middle Triassic Moenkopi Formation in Glen Canyon 

Table 7. Paleozoic Era fossils found in Glen Canyon National Recreation Area or its immediate vicinity.

Period and 

Epoch

Geologic Unit 

(map symbol) Fossils* Depositional Environment

Lower Permian

Cutler Group:

Cedar Mesa Sandstone

(P, Pc, Pcm)

Three published tracksites

(1) Dirty Devil Anomalopus (skink), Stenichus (beetle

(2) Grand Gulch tracksite Mostly synapsids (pelycosaurs,

other mammal relatives, and true mammals) with tracks

similar to Anomalopus (skink) and Chelichnus (reptile)

(3) Steer Gulch tracksite Similar tracks to those found at

Grand Gulch

Coastal sand dunes and evaporative 

sabkha environments

Lower Permian–

Upper Pennsylvanian

Cutler Group:

Lower Cutler beds

(Pc, PPNcl)

(old Rico Formation)

Marine invertebrate fossils (foraminifera, brachiopods, 

bivalves, gastropods, crinoids), elasmobranch teeth 

(including petalodont, bradyodont, and cladodont sharks)

Fluctuating sea levels in 

southeastern Utah Repetitive 

cycles of coastal dunes, channels, 

mudflats, tidal flats, supratidal 

areas, deltas, bays, bars, and open 

marine environments (Terrell 1972; 

Tweet et al 2009)

Lower Permian–

Upper Pennsylvanian

Cutler Group:

Halgaito Formation

(PPNhgl)

Extinct early amphibian Platyhystrix (“sail back” 

temnospondyl), sharks, crossopterygian fish (lobe fins), 

early ray-finned fish, amphibians, early tetrapods, early 

diapsid reptiles (includes lizards, snakes, and crocodilians), 

pelycosaurs, synapsids (“mammal-like reptiles”)

Lower Permian–

Upper Pennsylvanian

Cutler Group:

Elephant Canyon 

Formation (PPNe) 

Marine invertebrate fossils (foraminifera, corals, bryozoans, 

brachiopods, bivalves, gastropods, cephalopods, trilobites, 

echinoderms), invertebrate burrows, palaeoniscid fish, algal 

mats, wood fragments

Middle and Upper 

Pennsylvanian

Hermosa Group: 

Honaker Trail Formation 

(PNht, PNhtu, PNhtl) 

and Paradox Formation 

(PNp)

Marine invertebrate fossils (foraminifera, bryozoans, 

gastropods, crinoids, conodonts), algae, pellets, root traces 

(rhizoliths), borings in marine rocks

Normal, well-circulated marine 

environments In Arches National 

Park, 37 km (23 mi) north, fossils 

are from a variety of coastal 

settings, including delta lobes and 

tidal flats, as well as open marine 

environments (Wengerd 1962; 

Melton 1972; Millberry 1983; Tweet 

et al 2009; Doelling 2010) 

* Fossils from Tweet et al. (2009) and descriptions compiled in Willis and Ehler (in preparation; see glca_geology.pdf in GRI GIS dat
35

National Recreation Area, deposited approximately 

250 million to 240 million years ago, contains at least 

five tracksites (Mickelson et al. 2005, 2006; Kirkland et 

al. 2010). The Farley Canyon and Trachyte Point sites 

have been published and their tracks are listed in table 

8 (Lockley et al. 1998; Tweet et al. 2009). The formation 

also has vertebrate and invertebrate trace fossils similar 

to those found in Capitol Reef National Park and on the 

San Rafael Swell. Most of these are reptile traces, but 

there are also horsetail molds, millipede and horseshoe 

crab tracks, and fish bones that suggest the depositional 

setting was a broad flat coastal delta plain influenced by 

tidal and fluvial processes (Mickelson et al. 2006).

Stromatolites are the only fossils found in the Moenkopi 

Formation’s Hoskinnini Member in the recreation area 

(Tweet et al. 2009). These accretionary sedimentary 

structures grow in shallow marine water by trapping 

and binding fine-grained sediment in microbial mats. 

Exceptional living stromatolites are found today in the 

warm, relatively shallow waters of Australia’s Shark 

Bay, Utah’s Great Salt Lake, and a few other extreme 

environments around the world. Elsewhere on the 

Colorado Plateau, the lower members of the Moenkopi 

Formation contain marine invertebrates that indicate 

episodic incursion of shallow seas into the region 

during the earliest part of the Triassic (Tweet et al. 

2009).

Figure 20. Photograph of dinosaur tracks in the Powell Fossil Track Block tracksite, Glen Canyon National Recreation 

Area. The tracks are in a house-size block of Jurassic Navajo Sandstone (see table 7). National Park Service photograph 

by Vincent Santucci (NPS Geologic Resources Division).
36

Period and 

Epoch

Geologic Unit 

(map symbol) Fossils* Depositional Environment

Upper Cretaceous Straight Cliffs Formation

(Ksl, Ksj, Ksd)

Abundant fossils in the nearby Grand Staircase-Escalante 

National Monument.

Broad coastal plain that formed 

with sea level fall.

Upper Cretaceous Tropic Shale

(Kt)

Ammonites, bivalves, sharks, rays, turtles (Desmatochelys

and Naomichelys), and plesiosaurs from two short-necked 

lineages (pliosaurid Brachauchenius lucasi and polycotylids 

Eopolycotylus rankini, Palmulasaurus quadratus, and 

Trinacromerum? bentonianum). The polycotylid plesiosaur 

Dolichorhynchops with associated gastroliths (“stomach 

stones”) was found in an undesignated location.

Deposited during sea level rise 

and transgression of the Western 

Interior Seaway. Water depth in the 

area was less than 100 m (330 ft).

Upper Cretaceous Dakota Formation

(Kd)

Clams (Exogyra), oysters, plant fossils (especially angiosperm 

leaves), vertebrate tracks, and a dragonfly nymph.

Shifting environments from 

floodplains to coastal settings.

Upper Jurassic

Morrison Formation: 

Salt Wash Member

(Jms)

Sauropod tracks (Lost Spring Wash area). 

Semiarid seasonal savanna-like 

environment.

Upper Jurassic

Morrison Formation: 

Tidwell Member

(Jsmt)

Track of a small sauropod dinosaur (first sauropod track with 

skin impressions). Bone fragments. Termite nests. Pterosaur 

(Pteraichnus) tracks (Del Monte Mines area).

Middle Jurassic Entrada Sandstone

(Je) Some theropod and sauropod tracks. Semiarid to arid dune field.

Lower Jurassic Navajo Sandstone

(Jn)

Unionid clams

Dam tracksite: Eubrontes.

Crossing of the Fathers tracksite: in situ tracks of 

Otozoum (large prosauropod); Grallator tracks. 

West Canyon tracksite: multiple Otozoum and Grallatorlike tracks.

Last Chance Bay tracksite: Eubrontes-like biped.

Driftwood Canyon tracksite: small and large tridactyl 

tracks.

Hole in the Rock tracksite: three levels of tridactyl 

dinosaur tracks.

Slickrock Canyon tracksite: tracks on four fallen blocks 

of Eubrontes, Grallator, Anomoepus-like ornithopods, and 

Brasilichnium (mammal-like reptile).

Annie’s Canyon tracksite: two levels of tracks from 

Eubrontes, Grallator, and Otozoum.

Tapestry Wall: overhang site with Eubrontes-like tracks.

Orange Cliffs area: tridactyl tracks.

Onion Dome tracksite: Grallator and Anchisauripus.

Sand Hills Otozoum tracksite: Otozoum.

Powell Fossil Track Block: Grallator, Anchisauripus, and 

unknown tracks.

Tropical arid climate with seasonal 

monsoons. Eolian, playa, sabkha 

(salt flats), and lake (unionid clams) 

environments. Sahara-like desert 

with sand dunes moving westto-east, advancing over rivers of 

the Kayenta Formation. Water in 

interdunes formed oases. Fossils 

are mostly associated with oasis, 

interdune environments.

Lower Jurassic

Kayenta Formation

(Jk) 

Springdale Sandstone 

Member

(Jks)

Dinosaur tracks from multiple sites (6 described).

Explorer’s Canyon tracksite: Eubrontes dinosaur tracks 

(on display at the Page Visitor Center).

Long Canyon tracksite: elongate tracks.

Mike’s Mesa tracksite: Eubrontes tracks.

Slickrock Canyon tracksites (2 sites): Eubrontes and 

Grallator tracks.

Rainbow Bridge National Monument tracksite: 

Eubrontes tracks.

Shifting braided and meandering 

streams on a broad floodplain in a 

more humid climate than JTRw.

Lower Jurassic–

Upper Triassic

Wingate Sandstone 

(JTRw)

Lees Ferry and North Wash tracksites: Grallator tracks 

from the small theropod dinosaur.

The Rincon tracksite: tridactyl biped tracks.

First of several giant ergs in area. 

Also, playas.

* Fossils from Tweet et al. (2009) and Kirkland et al. (2010).

Table 8. Mesozoic Era fossils found in Glen Canyon National Recreation Area.
37

The Chinle Formation (TRc) contains abundant 

petrified wood and other plant fossils (table 8; Finnell 

et al. 1963; Tweet et al. 2009). In fact, the Chinle 

Formation’s Wolverine Petrified Forest that ranges into 

the northern part of Glen Canyon National Recreation 

Area represents an extensive fossil forest second only 

to the one preserved at Petrified Forest National Park 

(Tweet et al. 2009; Kirkland et al. 2010; see GRI report 

by KellerLynn 2010). Many localities in the park contain 

petrified wood (Santucci 2000). In 1985, a 9 m- (30 ft-) 

long petrified log was removed from Trachyte Canyon 

(Tweet et al. 2009). In 2009, a petrified log jam was 

documented in the Shinarump Member of the Chinle 

Formation in the San Juan arm (Vincent Santucci, 

written communication, 20 December 2015). Petrified 

wood in the Owl Rock/Petrified Forest Member is 

often black and more solidly petrified than in the other 

members. Large logs have been known to roll down 

slopes, remaining relatively intact (Kirkland et al. 2010).

Period and 

Epoch

Geologic Unit 

(map symbol) Fossils* Depositional Environment

Upper Triassic Chinle Formation, 

undivided

Variety of fossils including fossil wood, carbonaceous 

debris, gastropods, crayfish burrows, bones, coprolites, and 

dinosaur tracks.

Fourmile Canyon tracksite: tracks of the dinosaur-like 

Atreipus milfordensis and lizard-like Rhynchosauroides

(removed in 1992 and now part of the NPS collection).

Mike’s Mesa tracksite: tridactyl (three-toed) tracks.

Transition over time from braided 

streams in TRcs to a monsoonal 

climate in TRcmn and TRcms to an 

arid climate in the upper part of 

the unit.

Upper Triassic

Chinle Formation: 

Church Rock Member

(TRcc)

Petrified wood. Fish bones at The Rincon. Isolated ganoid 

(fish) scales in a block of sandstone, west side of The Rincon. Aridification continues.

Upper Triassic

Chinle Formation:

Owl Rock and Petrified 

Forest Members

(TRcop)

Owl Rock Member: permineralized wood, root traces.

Petrified Forest Member: petrified logs. Bone fragments 

of archosaurs and metoposaurs and unionid clam shell 

fragments from sites on north side of San Juan Arm.

Owl Rock: arid climate with 

carbonate soil horizons and small 

ponds on a floodplain.

Petrified Forest: deposited by 

streams.

Upper Triassic

Chinle Formation:

Moss Back Member

(TRcms)

Petrified logs, plant debris, possible tracks of Pentasauropus, 

a dicynodont (large mammal-like reptile).

Streams, crevasse splays, and 

floodplain settings.

Upper Triassic

Chinle Formation:

Monitor Butte Member

(TRcmn)

Red Canyon site has unionids (freshwater mussels), a small 

crocodile relative, coprolites, and lake fossils that include 

plants, insects, crustaceans, conchostracans, and fish fossils. 

Unit also contains logs.

Braided and meandering stream 

systems, lakes, and swamps in a 

monsoonal climate.

Upper Triassic

Chinle Formation:

Shinarump 

Conglomerate Member

(TRcs)

Fossils found in the vicinity of the recreation area are most 

commonly plants, including petrified wood, logs, pith 

casts, leaf compressions, pollen and spores, fragments of 

carbonized wood. Plant types include horsetails, ferns, 

fern-like plants, cycads, conifers, cycad-like bennettitaleans, 

and other gymnosperms. Other fossils from this unit include 

bone fragments, some of metoposaurs (extinct salamanderlike aquatic amphibians) or phytosaurs (extinct crocodilelike aquatic reptiles, tetrapod footprints, swim traces, and 

coprolites. Invertebrates include polychaete worm Spirorbis 

shells, two types of insect eggs, possible beetle feeding 

traces.

Braided streams filling valleys 

eroded into underlying strata.

Lower–Middle 

Triassic

Moenkopi Formation 

(TRm):

Upper and Lower 

Members, undivided

(TRmu, TRml)

Two published tracksites.

Farley Canyon site: horseshoe crab tracks, swim traces, 

lizard-like tracks.

Trachyte Point site: horseshoe crab tracks, swim marks.

Broad floodplain leading to a sea to 

the west and northwest.

Lower–Middle 

Triassic

Moenkopi Formation 

(TRm):

Hoskinnini Member

(TRmn)

Stromatolites. Periodically wet sabkha.

* Fossils from Tweet et al. (2009) and Kirkland et al. (2010).

Table 8. Mesozoic Era fossils found in Glen Canyon National Recreation Area, continued.
38

In addition to plant material, fossils in the Chinle 

Formation at Glen Canyon National Recreation Area 

include gastropods, crayfish burrows, bones, coprolites, 

and dinosaur tracks (table 8; Anderson et al. 2010). 

Dinosaur tracks have been reported from three sites, 

two of which have been published and are listed in table 

8 (Tweet et al. 2009). According to Kirkland et al. (2010), 

the plants, insects, crustaceans, conchostracans, and 

fish fossils discovered in the Monitor Butte Member 

(TRcmn) in Red Canyon may be the most significant 

collection of lake fossils ever discovered in the Triassic 

of western North America (table 8). 

Of all the Chinle Formation members, the Petrified 

Forest Member (TRcop) contains the most diverse 

assemblage of fossil vertebrates (Tweet et al. 2009). 

Vertebrate fossil sites are known in the recreation area, 

but they have not received serious attention yet (John 

Spence, written communication, 9 December 2015). 

At a site northwest of the recreation area, a diverse 

assemblage of fossil vertebrates has been found in the 

Petrified Forest Member (TRcop). The assemblage 

includes bones from lungfish, phytosaurs, and theropod 

dinosaurs (“beast-footed” bipeds), and an ornithischian 

(herbivorous bird-hipped dinosaur) like jaw (Parrish 

1999).

Chinle Formation fossils discovered in the nearby 

Grand Staircase-Escalante National Monument include 

carbonaceous debris, petrified logs, palynomorphs 

(organic microfossils like pollen and spores), bivalves, 

gastropods, ostracods, insects, horseshoe crabs, 

fish, reptiles, and tracks of phytosaurs, theropods, 

lepidosauromorphs (lizards, snakes, tuataras, and 

relatives), and prosauropods (herbivorous dinosaurs 

related to sauropods) (Foster 2002; Tweet et al. 2009). 

In Canyonlands National Park, the Petrified Forest, Owl 

Rock, and Church Rock Members (TRcop, TRcc) have 

yielded leaves, stems, needles, cones, wood, bivalves, 

gastropods, crayfish, conchostracans (clam shrimp), 

traces from crayfish and horseshoe crabs, metoposaurs 

(an extinct lizard), aetosaurs (an extinct order of 

armored herbivorous archosaurs), and phytosaurs (an 

extinct semi-aquatic reptile) (Hasiotis 1992; Tweet et al. 

2009).

Mesozoic Era Fossils: Jurassic Period

Significant Reptile Tracks

Fossils of the Jurassic Period in Glen Canyon National 

Recreation Area are dominated by dinosaur and reptile 

tracksites (table 8). Of the five tracksites in the Wingate 

Sandstone (JTRw), three have been documented (table 

8; Tweet et al. 2009). In addition to the tracks, a skull of 

the Triassic-age phytosaur Redondasaurus was found 

at the base of the Wingate Sandstone, outside of the 

park. Prior to this discovery, the Wingate Sandstone 

was thought to be entirely Jurassic in age. The skull, 

however, indicates that at least some of this formation 

was deposited in the Late Triassic (Lucas et al. 1997; 

Tweet et al. 2009). This discovery emphasizes the 

importance of documenting not only the fossil but also 

the stratigraphic level in which the fossil is found.

The overlying Kayenta Formation contains dinosaur 

tracks in many locations at Glen Canyon National 

Recreation Area and the immediate vicinity (Tweet 

et al. 2009). Eubrontes tracks represent the first large 

theropod tracks in the fossil record (Kirkland et al. 

2010). Large theropod tracks (Eubrontes) and small 

theropod tracks (Grallator) dominate the six described 

sites from the recreation area (table 8). While lake levels 

were still low, the Eubrontes tracks at the Explorer’s 

Canyon site were removed and are on display at the 

Page Visitor Center (Santucci and Kirkland 2010; 

Kirkland et al. 2010). Eubrontes tracks can also be found 

at Rainbow Bridge National Monument, but they are 

badly weathered.

An in situ Eubrontes track and a fallen slab containing 

more than 30 Grallator tracks were found in Slickrock 

Canyon (Tweet et al. 2009). The Grallator tracks in 

Slickrock Canyon are typical of the many tracks found 

in the transition zone between the Kayenta Formation 

and Navajo Sandstone (Tweet et al. 2009). Low water 

levels in Lake Powell have revealed even more tracks in 

this transition zone. Impressions of theropod heels and 

tracks from an animal moving at 22.4 km/hr (13.9 mph) 

were found in Chaol Canyon and 150 tracks were found 

at four sites in Slickrock Canyon. These tracks were left 

by small theropods, large theropods, and ornithischians 

(Lockley et al. 2005; Tweet et al. 2009). 

The Kayenta Formation on the Colorado Plateau also 

contains a diverse collection of vertebrate body fossils, 

which are summarized in Tweet et al. (2009). These 

body fossils are primarily found in the upper, siltier 

part of the Kayenta Formation, which is not widely 

exposed in Glen Canyon National Recreation Area. At 

the base of the Kayenta Formation, fossils are limited to 
39

semionotid (ray-finned) fish and dinosaur tracks in the 

medium-to-coarse sandstone and conglomerate of the 

Springdale Sandstone Member (table 8; Harshbarger 

et al. 1957; Smith and Santucci 1999). Coprolites, fish 

scales, and body fossils from crocodylomorphs, and 

tritylodontids (non-mammalian cynodonts) such as 

Kayentatherium may occur in the recreation area (Tweet 

et al. 2009).

Kayenta Formation fossils also include petrified wood, 

algal limestone, invertebrate trails and burrows, unionid 

bivalves, freshwater gastropods, and ostracods. As with 

the vertebrate fossils, these fossils are more prevalent in 

the upper, silty part of the formation (Tweet et al. 2009).

Most of the fossils from the Navajo Sandstone are 

associated with oasis deposits (Loope et al. 2004; Irmis 

2005; Tweet et al. 2009). These limestone deposits 

primarily yield plants and invertebrates. Body fossils 

are rare in the Navajo Sandstone, but in the last 

decade, important vertebrate body and trace fossils 

have been discovered (Irmis 2005; Vincent Santucci, 

written communication, 20 December 2015). They 

include specimens of tritylodonts, crocodylomorphs, 

sauropodomorphs, and theropods (Irmis 2005). 

Eubrontes, Anchisauripus, and Otozoum tracks are 

only known from interdune oases (Loope 2006). 

Tracks (identified as Batrachopus, Brasilichnium, and 

Grallator) of smaller dinosaurs are found in preserved 

sand dune deposits (Loope 2006). Irmis (2005) pointed 

out that this differentiation may reflect how the tracks 

were preserved in interdune compared to sand dune 

environments rather than the habitat range of the 

different species.

The first ten Navajo Sandstone tracksites in table 8 had 

been documented in Glen Canyon National Recreation 

Area prior to the 2009 paleontological resources 

inventory field study (Kirkland et al. 2010). Twentyeight trackways from prosauropods (Otozoum) and 

small theropods (Grallator) found at the most extensive 

in situ tracksite at the recreation area (Tweet et al. 2009).

The Dam tracksite, which had a single Eubrontes track, 

was destroyed during construction of Glen Canyon 

Dam. 

The 2009 field inventory discovered several 

undocumented tracksites (Kirkland et al. 2010). 

Many of these new sites were small, but the Onion 

Dome tracksite near the base of the Navajo Sandstone 

contained about 100 m (330 ft) of Grallator and 

Anchisauripus tracks in a playa deposit. The Sand Hills 

Otozoum and Powell Fossil Track Block tracksites have 

been recommended as paleontological interpretive 

sites (table 8; Kirkland et al. 2010). The Sand Hills 

tracksite contains excellent Otozoum tracks, which 

were likely from a long-necked herbivorous dinosaur 

(prosauropod) that was the precursor to the gigantic 

sauropods of the Late Jurassic. Otozoum is also an index 

fossil for the Early Jurassic, which means it is used to 

define and identify this geologic epoch.

The Powell Fossil Track Block tracksite was first 

reported in the summer of 2009 (fig. 20; Kirkland 

et al. 2010). Located near the base of the Navajo 

Sandstone, the tracksite preserves isolated theropod 

tracks and trackways (Grallator and Anchisauripus), 

and an unusual trackway of a large slow-moving 

bipedal dinosaur with tracks similar to iguanodontian 

ornithopods that do not show up in the geologic record 

for another 30 million–40 million years (Kirkland et al. 

2010). 

As with the Kayenta Formation, additional trackways in 

the Navajo Sandstone were exposed when the lake level 

dropped (Lockley et al. 2005). As of 2016, researchers 

and park staff had documented approximately 100 

tracksites in Glen Canyon National Recreation Area 

(John Spence, written communication, 9 December 

2015). In addition to dinosaur tracks, termite mounds, 

petrified wood, possible mammal-like tracks, and a 

reptile skeleton have been found in the vicinity of the 

recreation area (Hamblin 1998; Santucci 2000; Tweet et 

al. 2009; Santucci and Kirkland 2010). 

A unionid clam bed discovered in the Navajo Sandstone 

preserves a unique environment that existed among the 

Jurassic dunes (Kirkland et al. 2010). The bed, which 

is often submerged by Lake Powell, preserves molds 

of hundreds (perhaps thousands) of these freshwater 

bivalves. The unionid clam has a parasitic relation with 

fish, in that all unionid larvae spend part of their life 

cycle in the gill filaments of fish. The abundance of 

unionid clams suggests that fish were also present in 

this area during the Early Jurassic. In contrast to playas 

that formed in interdune sites when the water table 

impinged on the surface, this clam bed represents an 

environment with relatively permanent surface water 

within the Navajo Sandstone erg, which may be among 

the largest sand deserts in Earth’s history (Loope et al. 

2004; Kirkland et al. 2010; Milligan 2012). 
40

Although the Navajo Sandstone represents an immense, 

arid, active dune field, Early Jurassic tropical monsoons 

also impacted the western interior of the United States. 

Evidence of abundant rainfall can be found in the 

petrified trees found near Page, Arizona, at the southern 

tip of Glen Canyon National Recreation Area (Thomas 

2000). In situ fossil tree stumps, abundant dinosaur 

tracks, bioturbated strata as much as 20 m (66 ft) thick, 

and layers of stromatolites discovered outside of the 

park also suggest vibrant plant communities grew 

within this Sahara-like desert (Loope 1979; Loope et 

al. 2004). Some trees had diameters of almost 1 m (3 ft) 

while others lacked growth rings, indicating continuous 

growth. Thick-trunked cycadeoids, which first appeared 

in the Triassic Period and became extinct at the end of 

the Cretaceous Period, grew during times of increased 

precipitation. Araucarian conifers, whose living relatives 

include the hardy monkey puzzle tree (Araucaria 

araucana), grew along lake margins (Parrish et al. 2002; 

Wilkens et al. 2005, 2007; Parrish and Falcon-Lang 

2007; Tweet et al. 2009).

Trace fossils are the main fossils found in the Middle 

Jurassic Entrada Sandstone, the last major erg to 

cover the area. Some theropod tracks in the Entrada 

Sandstone have been found at Glen Canyon National 

Recreation Area, and in nearby Grand StaircaseEscalante National Monument, the Entrada Sandstone 

has yielded insect burrows, large vertebrate burrows, 

dinosaur tracks, and sand-swimming traces (Loope 

2004; Lockley et al. 2005; Graversen et al. 2007).

The Upper Jurassic Morrison Formation is famous for 

its dinosaur fossils, many of which are spectacularly 

displayed at Dinosaur National Monument (see GRI 

report by Graham 2006c; Gregson et al. 2010). As of 

2009, however, few Morrison Formation fossils had 

been reported from Glen Canyon National Recreation 

Area (table 8; Tweet et al. 2009). The most notable 

dinosaur fossil discovery has been several sauropod 

footprints with preserved skin impressions that 

were found in the Tidwell Member of the Morrison 

Formation (Jsmt) near Bullfrog (Tweet et al. 2009; 

Kirkland et al. 2010). This track proved to be the first 

sauropod track with skin impressions. 

In addition to dinosaur traces, termite nests in the 

Tidwell Member have been preserved in an unspecified 

location in the park (Engelmann 1999; Santucci 2000; 

Kirkland et al. 2010). The nests form cylindrical 

concretions 20 cm (8in) in diameter and 30–40 cm 

(12–16 in) tall.

Morrison Formation fossils have been found in nearby 

areas and include pterosaur tracks (Pteraichnus) 

from the Tidwell Member and sauropod tracks in 

the Salt Wash Member (Jms). Bone fragments and 

petrified wood have been found in Salt Wash Member 

paleochannels in Capitol Reef National Park, and fossils 

of plants, non-dinosaurian reptiles, and dinosaurs have 

been discovered in Grand Staircase-Escalante National 

Monument (Tweet et al. 2009). 

Mesozoic Era Fossils: Cretaceous Period

Fossils Within and Surrounding the Western Interior 

Seaway

During the Cretaceous, a major sea level rise drowned 

the terrestrial environments of southeastern Utah and 

created the Western Interior Seaway that bisected the 

North American continent (see the “Geologic History” 

chapter). The fossil diversity in the Upper Cretaceous 

Dakota Formation (Kd) records the transition from 

fluvial to coastal to shallow marine settings as sea level 

rose. Tweet et al. (2009) summarized the extensive 

paleobotanical fossils, dinosaur tracks, nonmarine 

fauna, and marine invertebrates common to the Dakota 

Formation. In Glen Canyon National Recreation Area, 

coal beds are found in the middle part of the formation, 

and fossils of clams (Exogyra) and oysters that lived in 

brackish to open marine environments are abundant in 

the upper sandstone (Anderson et al. 2010).

Potential Dakota Formation fossils that may be found 

in Glen Canyon National Recreation Area include 

those found in the adjacent Grand Staircase-Escalante 

National Monument and Kaiparowits Plateau. 

These fossils include palynomorphs, petrified wood, 

algae, foraminifera, bivalves, gastropods, ostracodes, 

ammonites, invertebrate traces, sharks, rays, rayfinned fish, lungfish, lizards amphibians, turtles, 

crocodilians and crocodile relatives, small theropods 

(dromaeosaurids and troodontids), tyrannosaurids, 

armored dinosaurs, hypsilophodonts (small bipedal 

herbivorous dinosaurs), hadrosaurids (duckbills), and 

mammals (marsupials, multituberculates, and nonmarsupial therian) (see Tweet et al. 2009 for references). 

The myriad marine fossils found in the Upper 

Cretaceous Tropic Shale (Kt) reflect deposition in the 

shallow waters of the Western Interior Seaway in this 
41

area (Tweet et al. 2009). Published sites in Glen Canyon 

National Recreation Area are from the southwestern 

part of the park and include ammonites, bivalves, 

sharks, rays, turtles, and plesiosaurs (table 8; Santucci 

2000; Albright et al. 2007a, 2007b).

When sea level fell later in the Cretaceous and the 

Western Interior Seaway shrank in size, coastal plain 

environments developed, and these environments are 

reflected in the fauna from each member of the Upper 

Cretaceous Straight Cliffs Formation. Only coal is 

known from the formation in Glen Canyon National 

Recreation Area, but exposures in Grand StaircaseEscalante National Monument have yielded abundant 

fossils, which may eventually be found in the recreation 

area (Tweet et al. 2009). The Tibbet Canyon Member 

(Ksl) yields marine invertebrates, sharks, rays, gars, 

crocodilians, and marsupials. The Smoky Hollow 

Member (Ksl) has dicotyledonous leaf compressions, 

sharks, rays, ray-finned fish such as bowfins and 

gars, the unusual amphibian Albanerpeton, frogs, 

turtles, lizards, crocodilians, small theropods (such 

as dromaeosaurids and troodontids), tyrannosaurids, 

armored dinosaurs, hypsilophodonts, hadrosaurids, 

and symmetrodont, marsupial, and possible eutherian 

mammals. Fossils from the John Henry Member (Ksj) 

include ammonites, bivalves, footprints, sharks, rays, 

ray-finned fish like bowfin and gars, Albanerpeton, 

frogs, turtles, lizards, crocodilians, dromaeosaurids, 

armored dinosaurs, hadrosaurids, and multituberculate, 

symmetrodont, and marsupial mammals. The Drip Tank 

Member (Ksd) in Grand Staircase-Escalante National 

Monument yields turtle and crocodilian fragments 

(Tweet et al. 2009).

Cenozoic Era Fossils: Quaternary Period

Pollen, Dung, Bromalites, and Bones

Quaternary fossils found in Glen Canyon National 

Recreation Area and its immediate vicinity have proven 

useful for both paleoecological and paleoclimatological 

reconstructions. Fossil pollen is especially valuable 

in these reconstructions as are the many fossils found 

in packrat middens (table 9; Tweet et al. 2009). For 

example, pollen analyzed from the dung in Bechan 

Cave indicated that the predominant plant community 

away from the riparian zone may have been sagebrush 

steppe rather the blackbrush (Coleogyne sp.), which is 

the dominant shrub today (Mead et al. 1984; Kirkland 

et al. 2010). Bones of large mammals such as sloths, 

proboscideans, equids, bison, and camelids are typical 

of Quaternary fossils found in the southern Colorado 

Plateau, and large mammal bones have been found in 

the recreation area (Tweet et al. 2009). A mammoth 

tracksite was discovered in Glen Canyon National 

Recreation Area near Forty-Mile drainage. 

Alcoves are important Quaternary fossil sites in Glen 

Canyon National Recreation Area (table 9). Most of the 

fossils found in the alcoves are associated with fossil 

dung. The best-known Quaternary site is Bechan Cave 

(fig. 21). This single-room cavern formed by spalling 

of cross-bedded sandstone and was aided by seepage 

and calcite crystal growth (Agenbroad and Mead 1989). 

The recessed alcove is 53 m (170 ft) deep, 32 m (100 

ft) wide, and up to 9 m (30 ft) high. Containing 300 m3

(10,600 ft3) of fossil dung, Bechan Cave lives up to its 

name, which means “big feces” in Navajo (Santucci et 

al. 2001).

Located on BLM land adjacent to Canyonlands 

National Park, Cowboy Cave, contains extensive 

archeological resources and Pleistocene dung deposits 

(Mead and Agenbroad 1992; Santucci et al. 2001). This 

large, one-room grotto provided the first radiocarbon 

dates (ranging from 13,040 to 11,020 years before 

present) for Mammuthus remains from the Colorado 

Plateau (Agenbroad and Mead 1989).

Microfossils, plant matter, and freshwater invertebrates 

have also been found in Quaternary fluvial sediments. 

Pleistocene bivalves and Holocene plant debris are 

present in the canyon near Bechan Cave (Agenbroad 

and Mead 1990). In Grand Staircase-Escalante National 

Monument, pollen and gastropods in Upper Valley 

Creek on the Escalante River date from the last 2,000 

to 200 years (Webb and Hasbargen 1997). Pollen, peat, 

and insects that provide paleoclimate information have 

been retrieved from the Lake Pagahrit site in the Lake 

Canyon area (Phillips 1995; Anderson et al. 2000).

Formations with Potential for Fossils in Glen 

Canyon National Recreation Area

As of 2009, the following formations had yet to yield 

fossils in Glen Canyon National Recreation Area, but 

fossils have been recovered from them elsewhere on the 

Colorado Plateau (Tweet et al. 2009). 

● Middle Pennsylvanian Paradox Formation (PNp).

Fossil fish fragments and abundant marine

invertebrates represent well-circulated, open
42

marine systems (Wengerd 1962; Rueger 1996; Tweet 

et al. 2009). 

● Lower Permian Organ Rock Formation (Po). In the 

Monument Valley area, fossils in stream channel 

deposits about 11 m (35 ft) from the base of the 

unit include sharks, fish, amphibians, reptile-like 

tetrapods, pelycosaurs, and tetrapod tracks (Tweet 

et al. 2009).

● Lower Permian Kaibab Formation (Pk). Abundant 

marine invertebrate fossils have been documented 

from the Fossil Mountain Member on the Colorado 

Plateau. About 72 m (235 ft) of the Kaibab is 

mapped in the Lees Ferry area where it consists 

of the Fossil Mountain Member overlain by the 

Harrisburg Member (Phoenix 1963; Anderson et al. 

2010).

● Lower Permian De Chelly Sandstone. Although 

not highly fossiliferous, this eolian unit contains 

trace fossils from invertebrates, such as spiders, 

scorpions, and beetles, and vertebrate tracks from 

pelycosaurs and Dromopus tracks from a lizard-like 

animal (Tweet et al. 2009).

● Lower Permian White Rim Sandstone (Pwr). 

Although rare, trace fossils have been reported 

from Canyonlands National Park (Baars and Seager 

1967).

● Middle Jurassic Carmel Formation (Jc). The lower 

Carmel Formation contains marine invertebrate 

fossils, and terrestrial trace fossils are found in the 

upper part of the formation (Tweet et al. 2009). 

● Middle Jurassic Summerville Formation (Jesu). 

Plant debris, a single sauropod tail vertebra, 

invertebrate traces, and a variety of vertebrate 

tracks are known from the Summerville Formation 

at Moab, Utah (Tweet et al. 2009). 

Figure 21. Photograph of Bechan Cave, Glen Canyon National Recreation Area. The alcove formed in Navajo 

Sandstone. Note the people for scale. Photograph courtesy of Tyler Knudsen (Utah Geological Survey). 
43

Paleontological Resources in a Cultural Resource 

Context

Because the archeological record at Glen Canyon 

National Recreation Area spans over ten thousand 

years, human artifacts found in archeological sites are 

commonly associated with paleontological resources 

(Geib and Fairley 1997; Agenbroad et al. 1989). For 

example, at least five cultural horizons dating from 

7,795 to 570 years BP have been recovered with fossils 

from the dung heaps in Bechan Cave (Agenbroad et 

al. 1989; Tweet et al. 2009). Remains of beans, corn, 

and squash were found along with artifacts such as 

sandals, bone beads, and a snare that were crafted from 

contemporaneous flora and fauna (Agenbroad et al. 

1989; Tweet et al. 2009). Cultural artifacts also include 

flake tools, projectile points, and scrapers fashioned 

Table 9. Quaternary Period fossils found in Glen Canyon National Recreation Area.

Epoch Site* Calibrated Radiocarbon 

Age* (years before present) Fossils

Holocene Near Lake Pagahrit Unknown Pollen, peat, and insects

Holocene Bechan Cave

(packrat midden) 1,523–1,306 Nine beetle taxa and a reduviid (assassin bug)

Holocene Cow Perfect

(packrat midden) 1,952–1,528 Two beetle taxa

Holocene Bowns (packrat midden) 10,160–9,423 Two beetle taxa

Holocene–

Pleistocene Oak Haven Alcove From 13,776 to 13,301 and10,588 to 10,184 Plant material; mammoth, bison, and shrubox dung

Pleistocene Withers Wallow Alcove 14,272–13,433 Plant material; mammoth, bison, bighorn sheep dung

Pleistocene BF Alcove From 14,728 to 13,632 and

14,023 to 13,270

Douglas fir needles, maple material, and two dung pellets 

possibly from a camel (Camelops)

Pleistocene Cottonwood Alcove From 15,188 to 14,018 Large dung pellets, some of which are from shrubox

Pleistocene Hooper’s Hollow Alcove

Oak twigs: 14,114–13,652

Middens: 15,926–15,132

Bison dung: 23,472–21,369

Plant material; a packrat midden; bison, shrubox, and 

bighorn sheep dung; bones from marmot, horse, and 

mountain goat

Pleistocene Bechan Cave From between 17,775 and 14,229 to 

between 13,781 and 13,221

Fungal spores, seeds, plant fragments, insects, charcoal, 

wood

Dung of packrats (Neotoma), cottontail rabbits (Sylvilagus), 

Shasta ground sloths (Nothrotheriops shastensis), 

mammoths (Mammuthus), ?horses (Equus), shrubox 

(Euceratherium collinum), bighorn sheep (Ovis canadensis), 

and mountain goats (Oreamnos harringtoni)

Hair from shrews, packrats (Neotoma), deer mice 

(Peromyscus), olive-backed mice (Perognathus), Abert’s 

squirrel (Sciurus aberti), small-footed bats (Myotis), coyotes 

(Canis latrans), bear (Ursus), horses, ground and mylodont 

sloths (Glossotherium and Nothrotheriops), mammoths, 

bison (Bison), bighorn sheep, and deer (Odocoileus)

Bones from toads (Scaphiopus intermontanus and 

S. cf. bombifrons), snakes (Crotalus and Pituophis), 

grouse-sized birds, marmots (Marmota), ground squirrels 

(Spermophilus), pocket gophers (Thomomys), voles 

(Microtus), packrats, rabbits (Brachylagus), and the extinct 

shrubox Euceratherium collinum (a tooth)

Packrat middens spanning the past 12,000 years

Pleistocene Mammoth Alcove From 20,341 to 19,218 Dung from mammoth, bison, and bighorn sheep; 

mammoth bones; gastropods from a nearby site

Pleistocene Shrubox Alcove From 23,100 ± 660 to between 

10,299 and 9,482

Oak twigs and dung from mammoth, shrubox, bison, 

mountain goat, and bighorn sheep

Pleistocene Oakleaf Alcove 24,600 ± 1,400 Dung (probably horse)

Pleistocene Grobot Grotto From 28,290 ± 2,100 to 

18,866–18,460

Plant material and mammoth, bison, shrubox, bighorn 

sheep, and mountain goat dung

* From Santucci et al. (2001) and Tweet et al. (200

Radiocarbon ages have been calibrated to yield calendar years before present (see Tweet et al. 2009
44

from chalcedony and/or petrified wood. 

In 1989, Agenbroad et al. correlated the cave data to 

alluvial deposits in the adjacent canyons in order to 

determine the relationship between episodes of human 

occupation and changing fluvial and environmental 

conditions. The canyon alluvial and cave sequences 

suggest that humans occupied the canyon and 

Bechan Cave during periods of floodplain stability 

and abandoned the region during periods when the 

floodplain was actively eroding (Agenbroad et al. 1989). 

Although not yet known at Glen Canyon National 

Recreation Area, pictographs and petroglyphs of 

dinosaur tracks have been found in the surrounding 

region. Petroglyphs of dinosaur tracks carved into 

Kayenta Formation rocks occur in Grand StaircaseEscalante National Monument and near Zion National 

Park (Staker 2006; Tweet et al. 2009).

Caves and Karst

Karst is a landscape that forms through the dissolution 

of soluble rock, most commonly carbonates such 

as limestone or dolomite (Toomey 2009). Caves, 

sinkholes, “losing streams,” springs, and internal 

drainage are characteristic features of karst 

landscapes. As of June 2016, cave or karst resources 

are documented in at least 159 parks, including 

Glen Canyon National Recreation Area. More 

information is available on the NPS Cave and Karst 

website, http://go.nps.gov/cavesandkarst (accessed 

20 June 2016).

Land et al. (2013) reported that Glen Canyon 

National Recreation Area could potentially contain 

karst landscape on about 23% of the recreation 

area. This figure was based on GIS analysis of a 

US Geological Survey national karst map (later 

published as Weary and Doctor 2014) which 

classified some of the sedimentary rocks in the park 

as “evaporite rocks at or near the land surface in a 

dry climate.” Such conditions are known to produce 

karst features in some areas. However, John Spence 

(Chief Scientist and Terrestrial Natural Resources 

Branch Chief at Glen Canyon National Recreation 

Area, written communication, 9 December 2015) is 

not aware of any karst topography in the park, with 

the exception of possible karst features in the Kaibab 

Limestone in the Lees Ferry area.

Paleozoic carbonate strata, especially in the Honaker 

Trail (PNht), Elephant Canyon (PPNe), and the Kaibab 

Formations (Pk) are potential sites for solution caves in 

Glen Canyon National Recreation Area. As mentioned 

in the “Alcoves and Hanging Gardens” section, 

numerous alcoves and caves have formed in the Navajo 

Sandstone and Cedar Mesa Sandstone cliffs (tables 3 

and 9).

Paleosols

As they do today, soils in the geologic past (paleosols) 

result from five major soil-forming factors: (1) parent 

material, (2) climate, (3) living organisms, especially 

vegetation, (4) topography, and (5) time. Study 

of paleosols, therefore, may provide evidence of 

paleoclimates. Many of the Mesozoic Era formations 

contain evidence of paleosol development, but typical 

paleosol characteristics, such as mottled reddish, 

greenish, and gray mudstone and siltstone, are 

especially abundant in the Owl Creek Member of the 

Chinle Formation (TRcop; fig. 22). Chinle paleosols 

exposed at the base of a channel sandstone between 

Figure 22. Photograph of paleosols in the Chinle Formation, 

between Twomile and Fourmile Canyons, Glen Canyon 

National Recreation Area. These paleosols formed on a 

floodplain and were then incised by a river that deposited 

the overlying, thick-bedded sandstone. Photograph from 

Anderson et al. (2010, figure 12).
45

Twomile and Fourmile Canyons are one of the “classic 

geologic sites” in Glen Canyon National Recreation 

Area (Anderson et al. 2010). The lighter-colored beds 

are typically carbonate (caliche) zones that, like today, 

formed near the ancient ground surface. Vegetation that 

grew in these developing soils is documented by lightcolored, steeply inclined veinlets of carbonate rock that 

represent root zones (Anderson et al. 2010).

Unconformities

An unconformity represents a substantial break or gap 

in the stratigraphic record, which results from either 

non-deposition over an extended period of time or 

erosion of previously formed strata. Unconformities 

often separate rock units representing different 

depositional environments. In Glen Canyon National 

Recreation Area, six regional unconformities mark 

major hiatuses (missing time) in the Mesozoic Era’s 

geologic record and are shown on the stratigraphic 

column for the recreation area (fig. 4). Unconformities 

have been identified in rocks of Triassic (TR), Jurassic 

(J), and Cretaceous (K) periods. Documenting 

unconformities is important to understanding the 

expanse of time represented by rocks and fossils in the 

area. Paleontologists and geologists do not always agree 

on the location and/or duration of unconformities. 

Continued scientific investigation may be able to further 

refine the interpretation of geologic history recorded in 

the rocks of the Colorado Plateau in general and Glen 

Canyon National Recreation Area in particular.

Triassic Unconformities

There are five unconformities in strata of the Triassic 

Period, and all of them except TR-2 have been 

recognized in Glen Canyon National Recreation 

Area (Pipiringos and O’Sullivan 1978; Dubiel 1994; 

Anderson et al. 2010). Two, TR-1 and TR-3, are regional 

unconformities that represent major episodes of 

erosion and/or non-deposition (fig. 4). All of the Triassic 

unconformities are associated with significant regressive 

(sea level fall) episodes (Dubiel 1994). 

The regional TR-1 unconformity marks the boundary 

between the Paleozoic and Mesozoic eras, a time 

when all the land masses were coming together to 

form the supercontinent Pangea. In the northern part 

of Glen Canyon National Recreation Area, the TR-1 

unconformity separates the White Rim Sandstone (Pwr) 

from the overlying Early Triassic Moenkopi Formation 

(TRm), and where the White Rim Sandstone is absent 

in the San Juan Arm, TR-1 separates the Moenkopi 

Formation from the Early Permian Organ Rock 

Formation (Stewart et al. 1972a). The unconformity 

represents several million years of elapsed time during 

which paleochannels were eroded into the Permian 

strata in southeastern Utah. The basal Hoskinnini 

Member (TRmh) of the Moenkopi Formation filled 

these paleochannels (Pipiringos and O’Sullivan 1978; 

Dubiel 1994). 

Nearly all of the Middle Triassic rocks were eroded 

from southeastern Utah during a regression that 

occurred after deposition of the upper part of the 

Moenkopi Formation. TR-3 represents those millions 

of missing Middle Triassic years prior to the deposition 

of the basal Shinarump Conglomerate Member (TRcs) 

of the Late Triassic Chinle Formation (fig. 4; Stewart et 

al. 1972b; Pipiringos and O’Sullivan 1978; Dubiel 1994). 

The TR-4 and TR-5 unconformities occur within the 

Chinle Formation and mark shorter intervals of missing 

time. The TR-4 unconformity separates the fluviallacustrine environment of the Monitor Butte Member 

(TRcmn) from the overlying fluvial system of the Moss 

Back Member (TRcms). The TR-5 unconformity 

separates the cliff-forming Church Rock Member (TRcc) 

from the underlying ledgy slopes of the Owl Rock and 

Petrified Forest Members (TRcop) (Lucas et al. 1997; 

Anderson et al. 2010).

Jurassic Unconformities

The contact represented by the J-1 unconformity, which 

separates the Lower Jurassic Navajo Sandstone (Jn) 

from the Middle Jurassic Temple Cap Formation, is one 

of the “classic geologic sites” referred to in Anderson 

et al. (2010). Features at the contact of the two 

formations include a lag of angular pebble- to cobblesize fragments of chert, breccia zones, large polygonal 

shrinkage (desiccation) cracks filled with sand from the 

overlying Temple Cap, carbonate nodules, extensive 

bioturbation, and weathering or bleaching that forms 

alteration zones up to 9 m (30 ft) thick. The J-1 surface 

also undulates over long distances, effectively reducing 

the thickness of the Navajo Sandstone by 60 m (200 ft). 

These features suggest that the surface was exposed to 

erosion for a long period of time prior to deposition of 

the Temple Cap (Anderson et al. 2010; Doelling et al. 

2013).
46

Correlating stratigraphic units and unconformities 

over great distances on the Colorado Plateau is 

challenging, and the relationship between the J-1 and 

J-2 unconformities remained a conundrum for many 

years. In Zion National Park, the J-1 unconformity 

separates the Lower Jurassic Navajo Sandstone (Jn) 

from the Middle Jurassic Temple Cap Formation, 

and the J-2 unconformity separates the Temple Cap 

Formation from the overlying Carmel Formation (Jc) 

(Pipiringos and O’Sullivan 1978; GRI report by Graham 

2006b; Doelling et al. 2013). East of Zion National 

Park, the Temple Cap pinches out, and previous 

reports suggested that the J-2 unconformity continued 

across southern Utah and cut out both the Temple 

Cap Formation and the J-1 unconformity (Pipiringos 

and O’Sullivan 1978; Peterson and Pipiringos 1979; 

Anderson et al. 2010). 

Recent field and isotopic age data collected in a regional 

study of the Jurassic in Utah, however, tell a different 

story. The study documents north–south trending 

paleotopographic highs in southern Utah and the 

eastward thinning of the Temple Cap Formation against 

these paleotopographic highs (Doelling et al. 2013). 

The Temple Cap Formation consists of sediments 

that were originally deposited on both sides of the 

paleotopographic highs. Isotopic ages indicate relatively 

little time separates Temple Cap from Carmel Formation 

deposition. In other words, the J-2 unconformity is a 

relatively minor, local unconformity. The J-1 and Temple 

Cap Formation in Zion National Park are interrupted 

by paleotopographic highs, but they continue to the east 

into Glen Canyon National Recreation Area (Doelling 

et al. 2013).

Isotopic age data from the Face Canyon area of Lake 

Powell indicate that Temple Cap sediments were 

deposited approximately 173 million to 170 million 

years ago. In the recreation area, the Temple Cap 

Formation is conformable with the overlying Carmel 

Formation (Jc) (fig. 4; Sprinkel et al. 2009; Anderson 

et al. 2010; Doelling et al. 2013). The GRI GIS data 

includes the Page Sandstone (Jp). Now, the Page 

Sandstone is restricted to areas south-southeast of Page, 

Arizona (Doelling et al. 2013), and many of the mapped 

areas of “Page Sandstone” should be considered Temple 

Cap Formation. Research continues on validating the 

regional significance of Jurassic unconformities in the 

recreation area (Anderson et al. 2010).

The regional J-3 unconformity is at the top of the 

Entrada Sandstone (Je) (fig. 4). The contact between 

the cliff-forming Entrada Sandstone and slope-forming 

Summerville Formation (Jesu) is easy to identify, but 

the J-3 unconformity becomes less obvious where the 

Romana Sandstone overlies the Entrada Sandstone 

(Anderson et al. 2010). The Entrada Sandstone is 

generally tannish-orange and rounded compared to the 

more reddish-brown, blocky sandstone of the Romana 

Sandstone.

The Romana Sandstone and Summerville Formation 

are considered equivalent in age because they are 

bounded by the J-3 and J-5 regional unconformities 

(the J-4 unconformity is not found in southeastern 

Utah) (Pipiringos and O’Sullivan 1978). The exact 

stratigraphic relationship between these formations 

is uncertain because erosion has removed these rocks 

from the Circle Cliffs uplift (figs. 4 and 23).

Erosion at the top of the Jurassic Morrison Formation 

(Jmb, Jms, and Jsmt) accounts for its varying thickness 

in southeastern Utah and resulted in the K-0 (also 

known as the sub-Cretaceous) unconformity (fig. 4). 

This regional unconformity represents a long gap in the 

rock record separating the Morrison Formation from 

the Late Cretaceous Dakota Formation (Kd).

Folds and Faults

The Laramide Orogeny folded and faulted the strata in 

the Glen Canyon area. Folds and faults are included as 

layers in the GRI GIS data. The folds are broad, northto northwest-oriented anticlines (convex, A-shaped 

folds) and synclines (concave, U-shaped folds). In 

general, the anticlines that intersect Glen Canyon 

National Recreation Area are asymmetrical, with steep 

eastern limbs and more gently dipping western limbs. 

The Circle Cliffs anticline is the most prominent fold 

in Glen Canyon National Recreation Area (fig. 23). 

The nearly 160-km- (100-mi-) long steep eastern limb 

of the fold is referred to as the Waterpocket Fold. The 

Waterpocket Fold is also referred to (and mapped) 

as a monocline, which is a one-limb, step-like fold in 

otherwise relatively horizontal or gently dipping strata. 

The Waterpocket Fold forms the principal geologic 

structural feature in Capitol Reef National Park (see 

GRI report by Graham 2006a). In Glen Canyon 

National Recreation Area, dips on the Waterpocket Fold 

are up to 15°, but north of the recreation area, dips can 

be greater than 60° (Doelling and Willis 2006, 2008; 
47

Morris et al. 2010). The west limb of the Circle Cliffs 

anticline, on the other hand, has dips of 4° or less. The 

anticline tilts to the south and crosses Lake Powell in 

The Rincon area (Willis 2004). 

In Glen Canyon National Recreation Area, the crest 

of the Circle Cliffs anticline is composed primarily 

of Navajo Sandstone (Jn). Near Iceberg Canyon, the 

Kayenta Formation (Jk) forms the steep slope of the 

Waterpocket Fold. A series of normal faults (fig. 24) 

extends north from Lake Powell for 20 km (12 mi) along 

the Waterpocket Fold. Rocks on the east side of these 

faults have moved down relative to the strata across the 

faults.

Pennsylvanian and Permian formations are exposed 

on the Monument uplift, a broad, north–southtrending, asymmetrical monocline in southeastern 

Utah and northeastern Arizona. The eastern limb of 

the Waterpocket Fold is the gently dipping west flank 

of the Monument uplift, a portion of which lies within 

the eastern part of the recreation area (Anderson et al. 

2010). North–south-trending secondary folds wrinkle 

the monocline along the San Juan Arm and include, 

from east to west, the Halgaito anticline, Cedar Mesa 

anticline, Slick Horn anticline, Moonlight syncline, 

North Organ Rock anticline, and South Organ Rock 

anticline (Anderson et al. 2010). 

Laramide deformation also produced the Kaiparowits 

and Henry Mountains basins. The axis of the Henry 

Mountains basin trends north-northwest between 

the Henry Mountains and the Circle Cliffs, and the 

southeastern part of the basin lies within the northcentral section of Glen Canyon National Recreation 

Area. The steeply dipping Waterpocket Fold forms the 

western limb of the basin (Anderson et al. 2010). 

North of Bullfrog Bay, the relatively small, northwesttrending Mule Creek anticline lies between the axis 

of the Henry Mountains basin and the Rock Spring 

syncline (Anderson et al. 2010). In the recreation area, 

the Salt Wash Member (Jms) of the Jurassic Morrison 

Formation forms the crest of the anticline, indicating 

that deformation occurred after Late Jurassic time. 

North of Bullfrog Bay, the axes of the Mule Creek 

anticline and the Rock Spring syncline merge with 

the central axis of the Henry Mountains basin, which 

proceeds to curve to the southwest, eventually merging 

with the axis of the Circle Cliffs anticline (see geologic 

map posters [in pocket]).

Several northwest-trending anticlines and synclines 

deform the Kaiparowits basin, which extends into the 

southern part of Glen Canyon National Recreation 

Area. From Fiftymile Mountain southwest to Marble 

Canyon, these folds include:

● Fiftymile Creek syncline

● Bridge anticline

● Hurricane Wash syncline

● Willow Tank anticline

● Lake Creek syncline

Figure 23. Schematic diagram across the Circle Cliffs anticline, which trends north–south to northwest–southeast 

through Glen Canyon National Recreation Area. The Waterpocket Fold defines the steep eastern limb and is the 

dominant structural feature in Capitol Reef National Park (plate 1). Diagram from Anderson et al. (2010, figure 22).
48

● Rock Creek anticline

● Croton Canyon syncline

● Rees Canyon anticline

● Last Chance Creek syncline

● Smoky Mountain anticline

● Warm Creek syncline

● Nipple Bench anticline

● Wahweap syncline

● Cedar Mountain anticline

These secondary folds developed over reversefaulted (compressional setting) (fig. 24), deeply buried 

Precambrian basement rocks (Anderson et al. 2010). 

The folds extend for tens of kilometers (miles). Minor, 

high-angled normal faults (extensional setting) (fig. 24) 

with less than 30 m (100 ft) of displacement parallel 

the axes of some anticlines (Anderson et al. 2010). The 

strata have dropped down on the west side of the fault 

relative to the east side.

Folds and faults create geologic structures that can trap 

oil, gas, or groundwater. According to Anderson et al. 

(2010), several unsuccessful oil exploration wells were 

drilled on the Mule Creek anticline and the secondary 

folds in the Kaiparowits basin. Folds and faults can 

also weaken the strata, which may then be more easily 

exploited by natural erosion or human activity. In 1880, 

Mormons took advantage of the weak, fractured rock 

in the Hole-in-the-Rock fault zone and built a primitive 

road through the canyon wall that dropped almost 

600 m (2,000 ft) to the Colorado River (Anderson et al. 

2010). 

Joints

Joints are fractures or breaks in bedrock surfaces, but 

unlike faults, they do not displace rock strata. Large 

joint sets, especially in the sandstones of the Wingate 

Sandstone (JTRw), Kayenta Formation (Jk), and Navajo 

Sandstone (Jn), are some of the more prominent 

features in Glen Canyon National Recreation Area. 

More than 4,100 joints are mapped in the GRI GIS data. 

Joint spacing depends on bed thickness and lithology, 

and in some areas, such as in the Navajo Sandstone 

south of Glen Canyon dam, the joints are closely 

spaced.

Three types of joints occur in Glen Canyon National 

Recreation Area: (1) near-vertical, (2) inclined, and 

(3) surficial (Anderson et al. 2010). Near-vertical 

and inclined joints were partly responsible for the 

development of slot canyons, rockfalls, and many 

natural arches in the recreation area. Many joints 

parallel the vertical canyon walls. Processes responsible 

for the near-vertical and inclined joints in these brittle 

sandstones include: (1) regional deformation of the 

Colorado Plateau during the Laramide Orogeny,

(2) regional uplift throughout the Cenozoic Era that 

led to the removal of thousands of feet of overlying 

Figure 24. Schematic illustrations of fault types. Movement occurs along a fault plane. Footwalls are below the fault 

plane and hanging walls are above. In a normal fault, such as those associated with the Waterpocket Fold, crustal 

extension (pulling apart) moves the hanging wall down relative to the footwall. In a reverse fault, crustal compression 

moves the hanging wall up relative to the footwall. Reverse faults are associated with deeply buried Precambrian 

basement rocks beneath Glen Canyon National Recreation Area. A thrust fault is similar to a reverse fault, but 

has a dip angle of less than 45°. In a strike-slip fault, the relative direction of movement of the opposing plate is 

lateral. When movement across the fault is to the right, it is a right-lateral (dextral) fault, as illustrated above. When 

movement is to the left, it is a left-lateral (sinistral) fault. A strike-slip fault between two plate boundaries is called a 

transform fault. Graphic by Trista Thornberry-Ehrlich (Colorado State University).
49

rock by erosion, and (3) local stresses such as laccolith 

intrusions (Anderson et al. 2010).

Surficial joints, also known as exfoliation or sheeting 

joints, form concentric, sheet-like layers that are 

roughly parallel to the surface topography. The origin 

of exfoliation joints has fascinated geologists for more 

than a century. Dense bedrock forms under great 

pressure deep within the Earth, and perhaps the most 

widely held hypothesis, included in textbooks for 

decades, suggests that exfoliation joints form when this 

confining pressure is released by erosion of overlying 

rock and sediment (Anderson et al. 2010). Another 

popular explanation for local surficial fractures involves 

the vertical grooves in Checkerboard Mesa, one of 

the “classic geologic sites” in Zion National Park. 

These shallow fractures may have formed as a result of 

freeze-thaw weathering where water in grooves freezes 

and expands in winter and thaws in summer, similar 

to freeze-thaw processes involved in the formation of 

natural arches (Biek et al. 2010).

Recent studies have shown, however, that simple relief 

of confining pressure will not open large fractures 

in massive rock bodies, such as those in the Navajo 

Sandstone (Martel 2004, 2006, 2011). Most eroded 

terrains contain no sheeting joints, and erosion typically 

does not produce the pull-apart stress perpendicular 

to Earth’s surface required to open such joints. Martel 

(2006, 2011) explained that surficial joints occur 

primarily in strong, dense rocks that have convex 

surfaces and are under strong horizontal compression. 

Greg Stock, Yosemite National Park geologist, and 

Allen Glazner, a professor at the University of North 

Carolina–Chapel Hill, illustrated how horizontal 

compression could open joints parallel to a convex 

surface if the curvature was sufficient and horizontal 

compression overcame both the force of gravity and the 

strength of the rock (Glazner and Stock 2010). 

Questions about surficial joint formation persist, 

including the nature of their interaction and 

propagation (Stock et al. 2012), the distances they 

extend, and their presence in slopes that are now 

concave (Martel 2006). Regardless of how they form, 

surficial joints have contributed to the impressive domelike structures above vertical canyon cliffs in the Navajo 

Sandstone (Anderson et al. 2010).

Laccoliths

The dome-shaped laccoliths of the Henry Mountains 

and Navajo Mountain contribute to the dramatic 

landscape and viewshed surrounding Glen Canyon 

National Recreation Area (fig. 25). Laccoliths, 

Figure 25. Photograph of Navajo Mountain. The domed shape of Navajo Mountain was caused by an igneous intrusion 

known as a laccolith. The Carmel and Entrada Formations overlie the cliffs of Navajo Sandstone that rise from lake 

level. High-level alluvial fans shed off Navajo Mountain cap outcrops of Entrada Sandstone. These fans are about 

500,000 years old. Photograph from Anderson et al. (2010, figure 19).
50

composed of intrusive igneous rock, form when 

magma is injected between bedding planes, causing 

the overlying sedimentary rock strata to dome or bow 

upward (fig. 5). Renowned geologist Grove Karl Gilbert 

first described laccoliths and designated the Henry 

Mountains as their “type locality” in 1877 (Gilbert 

1877). 

Five laccoliths form the five dome-shaped mountains 

that are collectively known as the Henry Mountains. 

These mountains include Mounts Ellen, Pennell, 

Hillers, Holmes, and Ellsworth, and they define the 

skyline north of Bullfrog and west of the northern part 

of the recreation area (plate 1). Each mountain consists 

of a “stock” (an igneous intrusion that cuts through 

strata) that provided a conduit for the laccolith’s 

magma. In the Henry Mountains, radiometric ages of 

the exposed igneous rock indicate that the laccoliths 

formed between 31.2 million and 23.3 million years 

ago, during the late Oligocene Epoch (Doelling 1975; 

Hunt 1980; Nelson et al. 1992). Cretaceous formations, 

exposed on the flanks of the Henry Mountains, are the 

youngest strata intruded by the magma. In the northern 

part of Lake Powell, Permian and Triassic formations 

dip gently west into a subtle syncline oriented parallel to 

Mounts Ellsworth and Holmes (Anderson et al. 2010).

The broad dome of Navajo Mountain outlines the 

eastern skyline in southern Glen Canyon National 

Recreation Area (fig. 25). However, in contrast to the 

laccoliths in the Henry Mountains and elsewhere 

on the Colorado Plateau, the igneous rock beneath 

Navajo Mountain is not exposed at the surface, and 

so very little is known about the laccolith’s formation 

(Anderson et al. 2010). At 3,166 m (10,388 ft) above 

sea level, Navajo Mountain is similar in elevation to 

the Henry Mountains. It has a diameter of 10 km (6 

mi). The Cretaceous Dakota Formation, which was 

deposited approximately 95 million to 100 million years 

ago, shapes the dome of Navajo Mountain, and like 

the Henry Mountains, it is the youngest exposed unit 

deformed by the laccolith (Anderson et al. 2010). The 

Navajo Mountain laccolith may have been emplaced 

at the same time as the Henry Mountains laccoliths 

or it may be age-equivalent to the Carrizo Mountains 

laccoliths in northeastern Arizona, which formed 

approximately 71 million to 74 million years ago in the 

Late Cretaceous (Semken and McIntosh 1997).

Unconsolidated Surficial Deposits

Although best known for the stark beauty of its bedrock 

landscape, Glen Canyon National Recreation Area 

contains a variety of unconsolidated surficial deposits 

dating from the middle Quaternary, about 1 million 

years ago, to the present (Anderson et al. 2010). The 

surficial deposits are in seven categories based on their 

depositional process: (1) alluvium (stream-deposited), 

(2) eolian (wind deposited), (3) slope movement (masswasting), (4) colluvium (water-, wind-, or gravitydeposited), (5) residuum (weathered in place),

(6) lacustrine (lake-deposited), and (7) tufa 

(evaporation).

Alluvium

Thirty-three alluvial and mixed alluvial units are in the 

GRI GIS data (“Qa” units), making alluvial deposits the 

most diverse group of surficial deposits in the recreation 

area (table 1). Anderson et al. (2010) categorized these 

deposits into three general types: (1) alluvium deposited 

by the large rivers, (2) alluvium deposited by local 

streams and washes, and (3) alluvial fans deposited 

at the mouths of washes and canyons and on large 

pediment-like benches (gently sloping bedrock surfaces 

at the base of mountains). The Unconsolidated Map 

Unit Properties Table (in pocket) contains a detailed 

description of all 33 units.

Clasts in the large river alluvium run the gamut of sizes 

from clay to large boulders (fig. 26). Constant grinding 

and knocking into one another resulted in well-sorted 

Figure 26. Photograph of clasts of river alluvium south 

of Antelope Island. The clasts consist of a variety of 

rock types, including quartzite, chert, metamorphic, and 

volcanic rocks. Photograph from Anderson et al. (2010, 

figure 18).
51

and well-rounded cobbles and pebbles. Some of the 

cobbles transported by the Colorado and San Juan 

rivers have their origins in Precambrian and Paleozoic 

rocks exposed in central and western Colorado, more 

than 240 km (150 mi) away (Anderson et al. 2010). 

These clasts are a mixture of all three general rock 

types: sedimentary, igneous, and metamorphic.

In contrast to the clasts found in large rivers, the clasts 

common along small streams and washes were locally 

derived, angular, and more poorly sorted because 

transport distance and transport velocity was less than 

in the Colorado and San Juan rivers. The boulders 

and cobbles consist of fragments of local sandstone, 

siltstone, and other rock types found in the recreation 

area. Volcanic and quartzite clasts derived from the high 

plateaus to the west are part of the alluvium in washes in 

the western part of the recreation area (Anderson et al. 

2010).

Alluvial fan deposits reflect a decrease in stream 

gradient and range in size from small fans at the 

mouths of small washes to large coalesced fans and 

fan remnants found on benches and mesas associated 

with the Henry Mountains, Navajo Mountain, the 

Kaiparowits Plateau, and other mesas in the area (fig. 

25). Clasts in the alluvial fans are generally poorly sorted 

and may contain large boulders transported by debris 

flows from intense summer afternoon thunderstorms 

(Anderson et al. 2010).

Alluvial deposits in Glen Canyon National Recreation 

Area are found in active channels and as erosional 

remnants (terraces) as much as 490 m (1,600 ft) above 

modern river level (Hunt 1969; Willis 2004, 2010a, 

2010b). These erosional remnants represent past river 

levels that were abandoned when the Colorado River 

and its tributaries vertically incised bedrock (fig. 27). 

Anderson et al. (2010) summarized the various methods 

that have been used to date these river terraces in order 

to calculate incision rates of the Colorado River and its 

tributaries (tables 1 and 2 in Willis and Ehler, in prep.). 

In central Glen Canyon National Recreation Area, the 

Colorado River incised bedrock at a rate of over 0.6 m 

(2 ft) per thousand years, which is one of the highest 

incision rates in any part of the Colorado River system. 

Between 500,000 and 250,000 years ago, the incision 

rate was 0.40 m (1.3 ft) per thousand years, and from 

250,000 years ago to the present, the incision rate has 

been 0.70 m (2.3 ft) per thousand years (Garvin et al. 

2005). These incision rates suggest that most of the 

canyon visible today was carved in the last one million 

years. This exceptionally high incision rate may have 

been aided by isostatic rebound (crustal unloading) 

following the rapid erosion of relatively nonresistant 

strata when the Grand Canyon was carved about 5.5 

million years ago (Pederson 2009; Lucchitta 1989).

Features in Holocene alluvium (Qal1) include smallscale trough cross-bedding, climbing ripple laminations, 

and imbricated cobbles. Similar features are found 

in terrestrial bedrock strata, indicating that the same 

fluvial processes acting today have occurred throughout 

geologic time. Holocene flooding has deposited humanmade debris up to 12 m (40 ft) above the modern river 

(Willis and Ehler, in preparation). If preserved in the 

rock record, these deposits will indicate the flow paths 

the rivers took on their way to the sea.

Eolian Deposits

Wind-blown sand (Qes), primarily derived from the 

easily weathered sand dunes preserved in the Navajo 

and Entrada Sandstones, accumulates in wind shadows 

and areas not affected by runoff during intense 

thunderstorms (Anderson et al. 2010). The deposits 

generally consist of well-sorted, rounded, fine- to 

medium-grained quartz sand (table 1). Eolian sand is 

also found associated with alluvial deposits (Qae, Qaeo, 

Qaec, Qea, Qeao). Wind-blown silt (loess) and clay 

commonly form dark-reddish-brown deposits found at 

higher elevations on the Kaiparowits Plateau.

Figure 27. Photograph of river-cut terrace near Oak 

Canyon, Glen Canyon National Recreation Area. Alluvial 

cobbles carried in by the Colorado and San Juan rivers 

and large boulders derived from old, high-level alluvial 

fans associated with Navajo Mountain cover this terrace. 

Photograph from Anderson et al. (2010, figure 20).
52

Water may leach wind-blown calcium-carbonate dust 

into the subsurface where it can accumulate to form 

caliche (calcic soil) deposits. These deposits are known 

as “hardpan,” a calcium-carbonate layer that ranges 

from a few inches to several feet thick (Anderson et al. 

2010). Because caliche takes time to accumulate, it can 

be a valuable age indicator (Birkeland et al. 1991).

Slope Movement (Mass-Wasting) Deposits

Slope movements are the downslope transfer of soil, 

regolith, and/or rock under the influence of gravity. 

Soil creep, rockfalls, debris flows, and avalanches are 

common types of slope movements. These processes 

and the resultant deposits are also known as “mass 

wasting” and commonly grouped as “landslides” (table 

1). Slope movements occur on time scales ranging 

from seconds to years, and most landslides continue to 

move, or have the potential to move, long after they are 

considered to be stable (Ashland 2003). The landslides 

in the recreation area record an ongoing process that 

has been active since the late Pleistocene (Willis and 

Ehler, in preparation). As is the case in many other 

parks, slope movements create geologic hazards and 

associated risks in Glen Canyon National Recreation 

Area. These hazards are addressed in the “Geologic 

Resource Management Issues” chapter of this report.

Landslides are common in the Triassic Chinle 

Formation (TRc), Triassic-Jurassic Wingate Sandstone 

(JTRw), and the Cretaceous Tropic Shale (Kt), but they 

also occur in the Morrison (Jm), Carmel (Jc), Kayenta 

(Jk), Moenkopi (TRm), Organ Rock (Po), Honaker Trail 

(PNht), and Paradox (PNp) Formations. The categories 

of slope movement deposits mapped in the Glen 

Canyon National Recreation Area include:

● Landslide and slump deposits (Qms): chaotic, 

extremely poorly sorted, massive blocks to clay-size 

material, some with obvious historic movement 

(Qmsh).

● Slump blocks (Qmsb): blocks that may be as 

much as 2.7 km (1.5 mi) long and typically rotate 

backwards and tilt toward the nearby cliff. The 

most common slump blocks are those of Wingate 

Sandstone that have slid onto the Chinle Formation.

● Talus deposits (Qmt): extremely poorly sorted, 

angular rubble deposited at the base of steep slopes. 

Some piles have an eolian sand mantle (Qmte).

The massive landslides and slumps that involve the 

Chinle Formation and the Wingate Sandstone are 

considered to be “classic geologic sites” by Anderson 

et al. (2010). Although the cliff-forming Shinarump 

Conglomerate Member (TRcs) of the Chinle 

Formation produces few landslides, the variegated 

claystones in the Monitor Butte Member (TRcmn) 

and Petrified Forest Member (TRcop, TRcu) trigger 

enormous landslides. These units contain abundant 

bentonite, a clay composed primarily of the mineral 

montmorillonite. Montmorillonite is one of the smectite 

group of minerals that form by the chemical alteration 

of volcanic ash in contact with water. The resulting 

chemical structure of smectitic minerals allows them to 

expand with the absorption of water and shrink upon 

desiccation, resulting in unstable slopes that give rise to 

abundant landslides. 

The stratigraphic juxtaposition of the highly erodible 

Chinle Formation below the cliff-forming Wingate 

Sandstone contributes to spectacular rockfalls and 

landslides. Erosion of the weaker Chinle Formation 

undercuts the Wingate Sandstone, and as a result of 

the lack of support, huge blocks detach from the cliff. 

The detached blocks may be quite large, up to several 

hundred meters across. Abundant vertical joints in 

the Wingate Sandstone help define the rock slabs 

that detach from the cliffs. Landslide deposits in the 

Chinle Formation often result in fresh landslide scarps 

and hummocky topography with blocks of Wingate 

Sandstone resting on the Chinle slopes (fig. 28). 

Extensive landslide deposits may be found in the Good 

Hope Bay area, the San Juan Arm, and at The Rincon 

(Anderson et al. 2010). 

According to Anderson et al. (2010), mass wasting has 

significantly increased along the Lake Powell shoreline 

as a result of three interrelated processes: 

(1) destabilization of clay minerals by water that 

constantly soaks deep into the bedrock, (2) dissolution 

of mineral cements, and (3) erosion of less resistant 

rocks by constant wave action, resulting in undercutting 

and destabilizing overlying cliffs and ledges. Landslides, 

rockfalls, and slumps (Qms) are especially common 

nearly everywhere the Chinle Formation is exposed 

above or just below the water line of Lake Powell 

(fig. 29). Lake water destabilizes the bentonite-rich 

members of the Chinle Formation. Spring runoff and 

water releases associated with power generation cause 

fluctuations in lake levels, which aggravate an already 

unstable position along the shoreline.
53

Mass wasting due to undercutting of overlying cliff- and 

ledge-forming units also occurs where the Straight Cliffs 

Formation (Ks) overlies the bentonite-rich claystones, 

mudstones, and shale in the Tropic Shale (Kt). Water 

percolates along joints to the base of the resistant 

sandstone where it perches on less porous clay and silt 

layers. The trapped water weakens cement, decreases 

friction, increases the load on the rocks, and can 

eventually cause bedrock to fail and slide down slope 

(Anderson et al. 2010).

In addition to triggering landslides, erosion in the 

Tropic Shale impacts paleontological resources (see 

“Paleontological Resource Inventory, Monitoring, and 

Protection” section). As of December 2016, monitoring 

protocols for measuring erosion in the Tropic Shale 

were being developed. In the interim, average erosion 

rates from available, albeit flawed, data range from 0.14 

cm/yr (0.06 in/yr) to 0.26 cm/yr (0.10 in/yr), which 

are relatively rapid compared with other units on the 

Colorado Plateau (Miller no date; available from John 

Spence, written communication, 9 December 2015). 

These erosion rates, which Miller considers to be 

conservative, suggest that 1.0 m (3.3 ft) of Tropic Shale 

will erode within either 715 years or 385 years. Large 

landslides of Tropic Shale scar the outcrops along 

the Straight Cliffs section of the Fiftymile Mountain 

escarpment (Anderson et al. 2010). 

Talus deposits (Qmt) are mapped in the Hite Crossing, 

Bullfrog, Lees Ferry, and San Juan Canyon areas, but 

they also occur in other areas (Willis and Ehler, in 

preparation). Eolian sand (Qmte) that mantles some 

talus deposits may be as much as 9 m (30 ft) thick.

Colluvium 

Colluvium consists of a mixture of unconsolidated 

sediments derived from alluvial, eolian, minor masswasting, and residual deposits (Anderson et al. 2010). 

Colluvium accumulates on moderate slopes in Glen 

Canyon National Recreation Area and is mapped with 

alluvial deposits (Qac, Qaco, Qaec). 

Residuum

Residuum consists of rock debris and sediment formed 

by weathering and essentially left in place after all 

but the least soluble constituents have been removed. 

Because sandstone is the most common rock type in 

Glen Canyon National Recreation Area, residuum 

primarily consists of sand weathered from these 

exposures. The residuum sand deposits often resemble 

wind-blown sand piles. Residuum is not mapped as 

a separate unit in the GRI GIS data for Glen Canyon 

National Recreation Area.

Figure 28. Photograph of landslide scarp along the east 

shore of Good Hope Bay, Glen Canyon National Recreation 

Area. The landslide developed in the Chinle Formation, and 

6–9 m (20–30 ft) of downward movement exposed a fresh 

surface (no desert varnish) of Wingate Sandstone. The talus 

blocks that mantle the Chinle slope are Wingate Sandstone 

and are not involved in the development of the landslide 

(they are just “along for the ride”) (Tyler Knudsen, Utah 

Geological Survey, geologist, written communication, 5 

December 2015). Note the vertical jointing in the Wingate 

Sandstone. Photograph from Anderson et al. (2010, figure 

13).

Figure 29. Photograph of cliff along the west shore 

between Twomile and Fourmile Canyons, Glen Canyon 

National Recreation Area. Erosion of the Chinle Formation 

(dark brown) undercuts the Wingate Sandstone, resulting 

in cliff collapse (note large boulders along water’s edge). 

Photograph from Anderson et al. (2010, figure 12).
54

Lacustrine Deposits

Lake deposits (Ql) in Glen Canyon National Recreation 

Area consist of thin, poorly consolidated silt, very 

fine-grained sand, peat, and clay (table 1). They are 

estimated to be as much as 10 m (30 ft) thick, but could 

be thicker. Middle Pleistocene lake deposits occur 

in an abandoned meander channel of the Colorado 

River in the Good Hope Bay area (Willis and Ehler, in 

preparation). 

Unusually thick lake deposits consisting of sand, silt, 

clay, and peat in Lake Canyon near Halls Crossing 

resulted from a lake called Pagahrit by the Piute Indians 

(Lyman 1963). The deposit records several lake cycles, 

with the oldest cycle dated at 5,180 radiocarbon years 

before present (Graf 1989; Pederson 2000). Lake 

Pagahrit formed behind a natural dam as much as 30 m 

(100 ft) high consisting of cottonwood, black willow, 

sand, and other debris flow deposits. The natural dam 

also served as a bridge until it was breached by an 

intense cloudburst in CE 1915 (Lyman 1963).

Tufa Deposits

Tufa is a chemical sedimentary rock composed of 

calcium carbonate and formed by evaporation. In Glen 

Canyon National Recreation Area, calcareous tufa (Qst) 

is associated with seeps and springs (table 1). The tufa 

cements bedrock and talus rubble, colluvium, and other 

surficial deposits. Tufa found below seeps and springs 

in many canyons in the recreation area may be 1–2 m 

(3–6 ft) thick. Extensive deposits of tufa are mapped in a 

small area in lower Red Canyon.

Questions remain to be answered regarding the age of 

the tufa deposits, the rate at which they formed, the 

effect of climate on the rate of tufa formation, and their 

potential to cover fossil resources (Kirkland et al. 2010). 

Kirkland et al. (2010) suggest that tufa deposits may also 

represent future fossil localities because the deposits 

contain plant and possibly animal remains.

Hite Delta Geomorphic Features

When Lake Powell reached full capacity in 1980, a delta 

immediately began forming in the lower reaches of 

Cataract Canyon, near the old town of Hite. The Hite 

delta grew rapidly because of the abundant sediment 

load of the Colorado River, which averaged ~24.7 x 106 

m3/year (~20,000 acre feet/year), and the narrowness of 

Cataract Canyon (Netoff et al. 2010).

Delta growth accelerated during the drought of 

2000–2005. Lake Powell lowered by more than 40 

m (131 ft) and large volumes of delta sediment were 

remobilized in addition to the normal load of sediment 

from the Colorado and Dirty Devil rivers. Incision by 

the Colorado River exceeded 10 m (30 ft) (Netoff et 

al. 2005, 2010). From 1999 to 2005, the delta advanced 

at a rate of almost 2.7 km/yr (1.7 mi/yr), growing to 60 

km (37 mi) long and extending almost to the mouth of 

White Canyon, ~6 km (3.7 mi) below the Hite marina.

Near-normal runoff returned in 2006, and by 2011, lake 

levels had risen by ~15 m (~50 ft) and again inundated 

much of the Hite delta (Netoff et al. 2010; Lake Powell 

Water Database 2016). Since 2011, average yearly lake 

levels have fallen by ~11 m (~37 ft). As of January 20, 

2016, the shoreline of Lake Powell was 14 m (47 ft) 

below the former Hite marina (Lake Powell Water 

Database 2016).

Exposure of the Hite delta offered researchers an 

opportunity to study the evolution of fluvial and 

lacustrine features and processes that are either 

rarely exposed or result from a non-seismic origin. 

Features include fluid/gas escape features (domes, mud 

volcanoes, and pockmarks), slumps and lateral spreads, 

and polygonal joint patterns (Netoff et al. 2010). 

These dynamic bio-geomorphic features and their 

transformations have analogs in marine sedimentary 

deposits, methane-dependent life forms, and methane 

contributions to global warming.

Domes, Mud Volcanoes, and Pockmarks

When lake levels started dropping in 2000, hundreds 

of closely-spaced, meter-decameter diameter domes 

were observed in the shallowing water. The domes had 

summit depressions from which a mixture of water, 

methane gas, and suspended sediment erupted. Rapid 

entrenchment of the Hite delta by the Colorado River 

exposed the domes, and many of them remained active, 

erupting muddy slurry that transformed the domes into 

steeper-sided cones known as mud volcanoes (fig. 30; 

Netoff et al. 2005, 2010). As their name suggests, mud 

volcanoes are surficial, volcano-shaped features that 

eject mud or silt (instead of lava) from a central vent 

(Dionne 1973; Reineck and Singh 1980). 

By December 2004, many of the volcanoes had 

collapsed, leaving shallow depressions on the surface 

of the Hite delta (fig. 31). The pockmarks ranged in size 
55

from 0.5 m (1.6 ft) to 7 m (23 ft) in diameter and 0.1 m 

(0.3 ft) to 0.5 m (1.6 ft) deep (Netoff et al. 2005, 2010; 

Livingston et al. 2014). Some of them remained active, 

emitting clear gases and fluids or a turbulent mixture of 

gases, fluids, and sediment. Once exposed, the viscosity 

of the extruded muds increased, resulting in the 

transformation of domes to mud volcanoes.

Lateral Spreads and Slumps

Incision by the Colorado and Dirty Devil rivers caused 

slumping and lateral spreading in the delta sediments. 

The slump blocks associated with the Colorado River 

are broadly arcuate, sub-parallel, and slightly tilted 

backward (Netoff et al. 2010). Direction of slumping 

has been towards the incised channel. The slump scarps 

range from 1 m (3 ft) to 5 m (16 ft) high and from 300 m 

(984 ft) to 530 m (1,739 ft) long. A nested series of semicircular, concentric scarps extends up the Dirty Devil 

delta beginning about 200 m (656 ft) from the mouth 

of the Dirty Devil River. The scarps extend up-stream 

for over 525 m (1,722 ft) (Netoff et al. 2010). The slight 

back-tilting and back-stepping of the slumps, combined 

with the drawdowns and incision of the Colorado River, 

suggest that the curved rupture surfaces become nearly 

horizontal (listric) at a relatively shallow depth.

Away from the incised channel, the slumps transform 

into lateral spreads on the Hite delta. The rupture 

surface and movement associated with lateral spreads 

is essentially horizontal (Netoff et al. 2010). Horizontal 

separation ranges from just a few meters to as much as 

40 m (131 ft). Surface ruptures resulting from slumping 

or lateral spreading do not appear to be related to 

domes and mud volcanoes.

Polygonal Joint Patterns

When lake levels dropped and the clay-rich delta beds 

were exposed, desiccation and shrinkage of the clays 

resulted in orthogonal, hexagonal, and radial joint 

patterns on the delta surface. Orthogonal joints (joints 

intersecting at right angles) dominate the joint patterns 

and are 5–15 cm (2–6 in) wide and can be over 0.7 m 

(2.3 ft) deep, indicating the clay-rich beds lost a large 

amount of volume during joint formation (Netoff et 

al. 2010). Columns bordered by the joints are typically 

20–35 cm (8–14 in) across. Hexagonal joint patterns 

occur locally, but they are often a mix of polygons with 

anywhere from 4 to 7 sides.

Mud volcanoes and pockmarks are dominated by 

radial joint patterns, which may be connected by 

orthogonal joints (fig. 31). Some radial joints formed 

prior to collapse, while others may have formed during 

subsidence and collapse.

Figure 30. Photograph of a mud volcano on the Hite delta, 

Glen Canyon National Recreation Area. Viscous, muddy 

sediment erupts long after subaerial exposure. Radial 

cracks form on the flanks of the mud volcano, probably 

from desiccation. Photograph from Netoff et al. (2010, 

figure 11). Used with permission from Utah Geological 

Association.

Figure 31. Photograph of a collapsed mud volcano on the 

Hite delta, Glen Canyon National Recreation Area. Many 

of the collapsed mud domes and mud volcanoes remained 

active following subaerial exposure, emitting clear gasses 

and fluids or a turbulent slurry. Radial joints formed, 

which may be a result of desiccation or stresses related to 

collapse. Photograph from Netoff et al. (2010, figure 12). 

Used with permission from Utah Geological Association.
56

Non-Seismic Triggering Mechanisms

Vibrations, especially from large earthquakes, often 

trigger fluid escape structures, slumps, and lateral 

spreads. These features in the sedimentary record 

indicate past or potential future seismic hazards. 

However, the features on the Hite and Dirty Devil 

deltas resulted from the release of methanogenic gas, 

channel incision, and loss of lateral support, rather than 

from seismic (earthquake) activity. Although several 

faults cut Permian strata in the vicinity of Hite, offset 

along these faults is small, and the faults do not cut 

Quaternary deposits, suggesting that any earthquake 

activity associated with the faulting was minimal (Netoff 

et al. 2010). In addition, only a few minor faults have 

been recorded in the region between 1990 and 2006 (US 

Geological Survey 2014). Documenting the geomorphic 

changes of these delta features may help researchers 

identify similar features in the rock record and to 

distinguish between seismic and non-seismic origins. 

Decaying organic matter buried in the sediment 

brought in by the Colorado and Dirty Devil rivers 

produced the methane gas that escaped through the 

central vents of the domes and mud volcanoes (Netoff 

et al. 2010; Livingston et al. 2014). Localized conduits 

probably formed in the delta sediments as fine-grained, 

low porosity and low permeability clay and mud 

accumulated on top of the more porous sediments. 

Increased pore water pressure may have resulted from 

dewatering of the delta sediments and also from leakage 

of the Cedar Mesa Sandstone. Pressure gradients 

resulting from methanogenic decay or organic material, 

pore water pressure from locally perched water 

bodies upslope on the delta surface, and underlying 

and adjacent water-saturated Cedar Mesa Sandstone 

were enough to fluidize and entrain unconsolidated 

subsurface silts, clay, and fine-grained sands as the gas 

escaped to the surface (Netoff et al. 2005). 

With subaerial exposure, pore water pressure 

decreased, causing the domes and mud volcanoes to 

collapse and leaving pockmarks on the delta surface 

(Netoff et al. 2010). The porous and permeable Cedar 

Mesa Sandstone lines the lower portion of Cataract 

Canyon and the narrow gorge of the Dirty Devil River. 

When lake levels are high, water seeps into the Cedar 

Mesa Sandstone. Dewatering of the sandstone when 

lake levels dropped provided at least some of the water 

pressure that enabled the exposed mud volcanoes and 

pockmarks to continue to erupt (Netoff et al. 2010).

Most of the clay minerals deposited on the deltas 

are derived from the montmorillonite-rich shale and 

mudstone of such Colorado Plateau units as the Chinle 

(TRc), Morrison (Jm), Mancos (Kmt), and Tropic (Kt) 

formations (Potter and Drake 1989; Netoff et al. 2010). 

Shrinkage of the clays upon exposure resulted in the 

polygonal jointing on the delta surface. The radial joint 

pattern on domes and mud volcanoes may be strictly 

desiccation features, or they may have been influenced 

by stresses created during doming.

Removal of lateral support as the Colorado River 

entrenched its channel triggered slumping and lateral 

spreading on the delta. Lateral spreads tend to occur 

where a somewhat competent surficial unit, in this case 

the partially dried mud, overlies water-saturated, noncohesive sediments under hydrostatic pressure, such 

as the coarser silts and sands that had previously been 

deposited.

Further research is needed to provide detailed 

morphological analyses of these features, the subsurface 

sediments and underground ‘plumbing’ associated 

with the pockmarks and mud volcanoes, the types of 

organic matter and microbes involved with the fluid/

gas escape structures, the similarity with features 

associated with seismic events, the potential for Martian 

analogues, and a comparison with similar features on 

other deltas, such as the San Juan delta (Netoff et al. 

2010). Furthermore, relatively new techniques such as 

ground penetrating radar (GPR) may be used to identify 

buried slump blocks and fluid escape conduits as lake 

levels rise. For example, in 2009 when lake levels rose to 

cover the Hite Delta and sediments infilled the incised 

channel, GPR recognized slump blocks, previously 

exposed topographic profiles, and large vertical fluid 

escape conduits (Degenhardt et al. 2009). Recognizing 

the geomorphic character of these modern features 

provides a guide for interpreting similar features 

preserved in ancient environments.

Economic Minerals

Tar Sands

Tar sands are a mixture of sand, clay, water, and 

bitumen, which is a black, syrupy, viscous oil. Tar sands 

near the surface are extracted from open-pit mines, 

such as those in northern Canada. Buried tar sands can 

be mined by injecting super-heated steam or igniting 

pockets of oxygen gas. Surface tar sands are transported 

to processing plants where the bitumen is separated 
57

from the sand using vibration and hot water. Subsurface 

bitumen is usually upgraded to synthetic-grade oil at a 

refinery.

Utah contains between 19.4 billion and 29.2 billion 

barrels of oil in tar sands, which is more than any other 

state in the United States (Bishop and Tripp 1993). 

For comparison, the much larger tar sand deposits 

in Alberta, Canada, contain an estimated 1.2 trillion 

barrels of oil (Huntoon et al. 1999). Most of the tar 

sands are located in the Uinta basin (northeastern Utah) 

and in southeastern-central Utah, where tar sands 

accumulated in three areas: the San Rafael Swell, Circle 

Cliffs, and Tar Sand Triangle (Bishop and Tripp 1993). 

The Tar Sand Triangle in southeastern Utah is the 

Figure 32. Map showing the location of the Tar Sand Triangle and road access. Road access to the bitumen deposit 

and the boundaries of Glen Canyon National Recreation Area are also shown. The dashed black line marks the 

approximate zero pinch-out boundary of bitumen-impregnated sandstones. Unpaved roads provide only limited access 

to the deposit. Tar Sand Triangle extent from Schamel (2013, figure 3) added to NPS map of Glen Canyon National 

Recreation Area. 
58

largest known tar sands deposit in the United States 

and intersects the northeastern portion of Glen Canyon 

National Recreation Area (fig. 32). The triangle is 

located on a deeply dissected plateau bounded on three 

sides by deep canyons formed by the Green River to 

the northeast, the Colorado River to the southeast, and 

the Dirty Devil River to the west. Bitumen-saturated 

sandstone at least 30 m (100 ft) thick covers an area of 

218 km2 (84 mi2) (Dana et al. 1984; Huntoon et al. 1999; 

Schamel 2013). A recent rigorous analysis of the Tar 

Sand Triangle estimated a total of 4.7 billion–5.6 billion 

barrels of in-place oil in a deposit exceeding 520 km2

(200 mi2) in size (Schamel 2013).

Tar sand in the Tar Sand Triangle occurs primarily in the 

eolian sandstones of the White Rim Sandstone (Pwr), 

although tar sands have also been found in the upper 

Cedar Mesa Sandstone (Pcm) and the sandy basal part 

of the Moenkopi Formation (TRml). Although the White 

Rim Sandstone is only as much as 26 m (85 ft) thick in 

the Hite area, it thickens rapidly to over 60 m (200 ft) 

to the north and northwest. Average porosity (15–20%) 

and permeability (200–500 millidarcies) values for 

the White Rim Sandstone are relatively high, but oil 

saturation averages 30–35%, which is considered to 

be low (Schamel 2013). Beds in the Tar Sand Triangle 

gradually tilt to the west-southwest at about 37 m (120 

ft) per mile (fig. 33; Huntoon et al. 1999; Schamel 2013).

Processes involved with oil migration into the White 

Rim Sandstone took advantage of tectonic plate 

collisions and the stratigraphic relationship between the 

porous White Rim Sandstone and relatively non-porous 

overlying strata. The collision of an oceanic plate with 

the western margin of North American during the Late 

Jurassic to the Eocene (Sevier and Laramide orogenies) 

caused west-to-east thrusting that stacked large 

thrust sheets on top of one another. Prior to tectonic 

deformation, many of the Pennsylvanian and Permian 

aquifers were hydrologically connected (Sanford 1995). 

Thrusting shortened central Utah by about 120 km (190 

mi), and the huge thrust sheets may have acted, as Oliver 

suggested, like “giant squeegees” to hydrodynamically 

force long-distance oil migration into southeastern Utah 

(Oliver 1986, p. 99). 

Thermal modeling of the White Rim Sandstone’s 

burial history indicates that oil migrated into the Tar 

Sand Triangle when the unit was at maximum burial 

depth and temperature, near the end of the Laramide 

Orogeny approximately 35 million to 40 million 

years ago (Huntoon et al. 1999; Whidden et al. 2014). 

Figure 33. Schematic geologic cross-section through the Tar Sand Triangle. The “drop pattern” represents the thickness 

of the bitumen deposit in the White Rim Sandstone (Pwr). The blue line marks the oil/water contact. Vertical scales are 

elevations above mean sea level. Diagram modified from Schamel (2013, figure 5).
59

Oil migration was aided by vertical faults that offset 

formations below the White Rim Sandstone and by 

regional unconformities, which may provide excellent 

conduits for migrating fluids (Huntoon et al. 1994, 

1999). Rocks in contact with Laramide faults on the 

eastern side of the Paradox Basin are often lighter 

colored than strata away from the faults. This bleaching 

effect resulted from migrating reducing fluids, such as 

petroleum (Breit and Meunier 1990).

Oil migrated into gently dipping, porous sandstones in 

the Tar Sand Triangle and was trapped by the up-dip 

unconformable contact with non-porous Triassic strata 

(Dana et al. 1984; Huntoon et al. 1999; Schamel 2013). 

Down-dip, the oil floats above an oil-water contact at 

elevations of 1,280–1,420 m (4,200–4,650 ft) above sea 

level (fig. 33). 

Basin-and-Range faulting in the Miocene Epoch 

disrupted oil migration by severing and fragmenting 

the permeable strata and unconformities in western 

Utah (Huntoon et al. 1999). Uplift of the Colorado 

Plateau eventually exhumed the White Rim Sandstone. 

Dead oil (crude oil containing very little dissolved gas) 

is found in the White Rim Sandstone on both sides of 

the Colorado and Green rivers in the Canyonlands 

area, suggesting that migration took place before the 

Green River dissected the White Rim Sandstone in the 

Oligocene–Miocene epochs (Gardner 1975; Huntoon et 

al. 1999). 

Neither the direction of migration nor the source of 

the oil in the White Rim Sandstone is well defined. 

The black shales in the Paradox Formation (PNp) and 

the Honaker Trail Formation (PNht) are the primary 

source rocks for the Paradox Basin, east of the Tar Sands 

Triangle (Whidden et al. 2014). To the north, in central 

Utah, geochemical analyses have identified Permian 

and Cretaceous oil sources in the Uinta Basin, SanpeteSevier Valley area, and the Wasatch Plateau (Sprinkel et 

al. 1997). Discovered in 2004 after more than 50 years 

of unsuccessful exploration in the area, the Covenant 

oil field in north-central Utah produces Pennsylvaniansourced oil from Navajo Sandstone reservoirs (Chidsey 

et al. 2007). None of these sources, however, are a 

geochemical match for the heavy oil found in the White 

Rim Sandstone. Rather, geochemical analyses suggest 

that the oil in the Tar Sand Triangle migrated from 

Mississippian and/or Permian age source rocks found to 

the distant west and northwest. To reach the tar sands, 

the oil had to migrate over 100 km (60 mi) eastward 

(Sandberg and Gutschick 1984; Huntoon et al. 1999; 

Whidden et al. 2014).

Development of tar sands in southeastern Utah 

poses a potential resource management issue, which 

is discussed in the “Abandoned Mineral Lands and 

Potential Mining Activity” section.

Gold

Much of the river gravel in Glen Canyon National 

Recreation Area eroded from the mountains of 

Colorado. Along with gravel, gold was transported 

downstream from Colorado’s many gold deposits. Early 

prospectors found gold in most gravel bars, but the 

gold is “flour gold,” which occurs as tiny specks about 

the size of finely sifted flour. Placer gold mines were 

developed in the region, including in the recreation 

area, but these very fine gold particles proved very 

difficult to separate from silt and clay and none of the 

mines were profitable (Anderson et al. 2010). Currently, 

gold mining is not a resource management issue for the 

recreation area.

Uranium

On the Colorado Plateau, uranium occurs in sandstones 

and conglomerates of the Shinarump Conglomerate 

Member (TRcs) of the Triassic Chinle Formation and in 

the Jurassic Morrison Formation (Jm). The Morrison 

Formation is famous for both uranium and dinosaur 

bones, although only uranium has been found in Glen 

Canyon National Recreation Area (Anderson et al. 

2010). Uranium-bearing fossil logs are present in the 

Chinle Formation. Past uranium mining has resulted in 

geologic resource management issues for the recreation 

area (see the “Geologic Resource Management Issues” 

chapter).

Coal

Coal beds are found throughout the Colorado Plateau, 

especially in the Late Cretaceous Straight Cliffs 

(Ks) and Dakota (Kd) formations (Anderson et al. 

2010). The John Henry Member of the Straight Cliffs 

Formation (Ksj) contains the major coal resources on 

the Kaiparowits Plateau, northwest of Glen Canyon 

National Recreation Area (Hettinger 2000; Anderson 

et al. 2010; Doelling et al. 2010). The Kaiparowits 

coalfield lies within Grand Staircase-Escalante National 

Monument, and as of 2010, it contained 60.7% of 

Utah’s estimated recoverable coal (Vanden Berg 2011). 
60

Locally, coal beds in the John Henry Member can be 6 

m (20 ft) or more thick. 

Coal beds in the Dakota Formation are thinner and 

discontinuous. Most of the beds occur in the sandstone, 

mudstone, and bentonitic claystone of the middle 

unit (Anderson et al. 2010). Coal beds formed in the 

Dakota Formation during the Late Cretaceous rapid 

transgression that produced the Western Interior 

Seaway. Because regression of the seaway occurred 

more slowly, thick peat beds formed in swamps and 

lagoons. Upon burial, which was accompanied by heat 

and pressure, these peat beds became the coal beds 

of the Straight Cliffs Formation. The Surface Mining 

Control and Reclamation Act of 1977 (30 USC § 1201 

et. seq.) (SMCRA) prohibits surface coal mining 

operations on any lands within the boundaries of a NPS 

unit, subject to valid existing rights. See the “Mineral 

Leasing” and “Coal Mining” sections.

Geologic Type Sections

A type section is an area where a sequence of strata 

was originally described. The type section serves as 

an objective standard with which to compare spatially 

separated strata (fig. 34). Preferably, a type section is 

designated in an area where the unit shows maximum 

thickness and both the top and bottom of the unit are 

exposed. Designated (“official”) and undesignated 

(a specific location is not designated, but general 

area is known) type sections of 11 formations occur 

in Glen Canyon National Recreation Area or its 

immediate vicinity (table 10). The US Geological Survey 

“GEOLEX” website provides location information and 

nomenclatural summaries for geologic map units across 

the country and is a source of additional information: 

http://ngmdb.usgs.gov/Geolex/search (accessed 25 

August 2015).

Type sections are typically selected for layers of 

sedimentary rocks which share similar characteristics, 

such as rock type (e.g., sandstone, shale, siltstone), 

color, or distinctive features. Such a rock unit is called 

a “formation.” Geologists usually name formations to 

reflect a geographic feature such as a river, mountain, 

or city where the layers are best seen (e.g., Wahweap 

Formation). Formations can be lumped together 

into “groups” (e.g., Hermosa Group) or subdivided 

into “members” (e.g., Moss Back Member of Chinle 

Formation).

Figure 34. Photograph of the Page Sandstone at its type 

locality on Manson Mesa, Arizona. The Page Sandstone 

is separated from the Navajo Sandstone by the J-1 

unconformity. Photograph from Anderson et al. (2010, 

figure 28A).
61

Table 10. Designated and unofficial type sections for formations within or in the vicinity of Glen Canyon National 

Recreation Area.

Period and 

Epoch

Geologic Unit 

(map symbol) Type Location(s) Official 

Designation Reference

Upper Cretaceous Wahweap Formation

(Kw)

Probably named for exposures along Wahweap 

Creek that drains into Wahweap Bay, northwest of 

Antelope Island

No Gregory and Moore (1931)

Upper Cretaceous

Straight Cliffs 

Formation

(Ks)

Straight Cliffs in Escalante Valley. Yes Gregory and Moore (1931

Upper Jurassic Romana Sandstone

(Jr)

Romana Mesa in the southern part of the 

recreation area north of The Sand Hills (north side 

of Lake Powell)

Yes Peterson (1988)

Middle Jurassic Page Sandstone

(Jpt)

Northwest side of Manson Mesa near Page, AZ (fig

35). Thins from 90 m (300 ft) at its type section to

27–60 m (90–200 ft) in the recreation area

Yes Peterson and Pipiringos 

(1979)

Lower Jurassic Navajo Sandstone

(Jn)

Named from the “Navajo Country” of AZ, UT, and 

NM. Yes Gregory and Stone (1917

Lower Permian White Rim Sandstone

(Pwr)

Topographic bench called White Rim, between the 

Green and Colorado rivers, Canyonlands National 

Park

No Baker (1929)

Lower Permian

Organ Rock 

Formation

(Po)

Natural monument known as Organ Rock, south of 

the San Juan Arm in San Juan County, UT. No Baker (1929

Lower Permian

Cedar Mesa 

Sandstone

(Pcm)

Cedar Mesa, north of the eastern end of the San 

Juan Arm. Yes Baker (1929

Lower Permian–

Upper Pennsylvanian

Halgaito Formation

(PPNhg) Halgaito Spring, southwest of Mexican Hat. Yes Baker (1929

Upper Pennsylvanian

Elephant Canyon 

Formation

(PPNe)

Elephant Canyon in Canyonlands National Park. Yes Baars (1962

Upper Pennsylvanian

Honaker Trail 

Formation

(PNht)

Honaker Trail, about 0.8 km (0.5 mi) east of th

recreation area near the Goosenecks of the San 

Juan River

Yes Wengerd and Matheny 

(1958)

Refer to US Geological Survey GEOLEX for additional information about type sections: http://ngmdb.usgs.gov/Geolex/search (accessed 21 June 201

63

Geologic Resource Management Issues

This chapter describes geologic features, processes, or human activities that may require management 

for visitor safety, protection of infrastructure, and preservation of natural and cultural resources in 

Glen Canyon National Recreation Area. The NPS Geologic Resources Division provides technical and 

policy assistance for these issues.

During the 1999 scoping meeting (Geologic Resources 

Division and Natural Resources Information Division 

1999) and 2015 conference call, participants (see 

Appendix A) identified the following geologic resource 

management issues:

● Landscape Safety Hazards

● Slope Movement Hazards and Risk

● Flash Floods and Debris Flows

● Paleontological Resource Inventory, Monitoring, 

and Protection

● Cave and Alcove Management

● Sediment Deposition in Lake Powell

● Abandoned Mineral Lands and Potential Mining 

Activity

● Potential Impacts from Global Climate Change

● Earthquakes

● Glen Canyon Dam and Downstream Impacts to the 

Colorado River

● Navajo Sandstone and Potential Glen Canyon Dam 

Failure

Resource managers may find Geological Monitoring

(Young and Norby 2009; http://go.nps.gov/

geomonitoring) useful for addressing these geologic 

resource management issues. The manual provides 

guidance for monitoring vital signs—measurable 

parameters of the overall condition of natural resources. 

Each chapter covers a different geologic resource 

and includes detailed recommendations for resource 

managers, suggested methods of monitoring, and case 

studies.

The Foundation Document for Glen Canyon National 

Recreation Area (National Park Service 2014a) 

identified current conditions and trends, challenges 

and opportunities, existing data and plans, data or 

GIS needs, planning needs, and applicable laws, 

executive orders, regulations, and policies associated 

with fundamental resources in the recreation area. 

Those resources are heritage resources, Lake Powell, 

landscape, paleontology, and water. Information is 

provided here for geologic resources, many of which 

contribute to the fundamental resources of the 

recreation area.

Landscape Safety Hazards

As with any canyon environment, the landscape 

poses safety hazards for hikers, climbers, and unwary 

sightseers (fig. 35). In spring 2014, Sarah Doyle, physical 

scientist at Glen Canyon National Recreation Area, 

compiled a list of geohazards, primarily from incident 

reports. Her list included detailed descriptions of each 

event, whether the incident was natural or humancaused, the rock type associated with the incident, and 

the date, time, and locality of each incident. Eighteen of 

the thirty-one reported incidents resulted in fatalities 

and were caused by rockfalls, landslides, flash floods, 

rock climbing, slipping on trails, or falls from the cliffs 

in the Kaibab Formation (Pk), Navajo Sandstone (Jn), 

and Salt Wash Member of the Morrison Formation 

(Jms) (Sarah Doyle, Glen Canyon National Recreation 

Area, physical scientist, written communication, 4 May 

2015). 

Moqui marbles contribute to potential slipping on 

trails that traverse the Navajo Sandstone (Jn). These 

iron-coated concretions, for example, are scattered on 

the friable sandstone surface of the popular Horseshoe 

Bend Trail (fig. 36). The National Park Service sign at 

the trailhead advises caution because the rocks may be 

unstable, the terrain uneven, and the viewpoint has no 

railing (fig. 35).

The Foundation Document for Glen Canyon National 

Recreation Area considers identifying landscape 

hazards and high-risk zones to be a medium priority 

for the park (National Park Service 2014a). Visitors 

approach the edge of cliffs in the recreation area to get 

a better look at the impressive landscape, but unstable 

conditions may lead to landslides, rockfalls, and other 

slope movement hazards discussed in the following 

section.
64

Slope Movement Hazards and Risk

As described in the “Unconsolidated Surficial Deposits” 

section, slope processes are common throughout Glen 

Canyon National Recreation Area (fig. 37). Although 

they may appear to be inactive, landslides and other 

slope movements may continue to move by slow creep, 

may be reactivated, and continue to pose a risk (Ashland 

2003). Slumps and slides (Qms and Qmsb) are common 

where erosion of less resistant strata oversteepens 

slopes and undercuts the more resistant sandstone cliffs 

and ledges (fig. 29). These natural processes become 

issues when visitors or boaters travel or camp near the 

base of the cliffs or atop overhanging ledges. Potentially 

hazardous areas include those with visible cracks, loose 

material, or overhangs. Fatal rockfalls have occurred 

where people were standing on ledges that collapsed or 

were struck by rocks falling from above. 

Rockfalls from overhanging alcoves and cliffs may occur 

without warning, making camping or boating beneath 

the overhangs potentially dangerous. Slabs of rock have 

fallen onto boats and caused fatalities in the recreation 

area. 

Figure 35. Photograph of visitors overlooking the popular Horseshoe Bend, Glen Canyon National Recreation 

Area. Much of the lighter-colored, cross-bedded sandstone that is supporting the darker ledge upon which the 

photographer is standing has fallen away, and what remains is nearly detached from the cliff face. Some visitors set up 

tripods on this ledge to get a photograph of the entire meander. Signs at the overlook and the trailhead (inset photos) 

include warnings to “not stand on the edge” and to “be aware of where you are standing.” Overlook photograph 

courtesy of Tyler Knudsen, Utah Geological Survey. Sign photographs by Eric Bilderback (NPS Geologic Resources 

Division) in February 2014.
65

Ten of the 16 rockfalls documented by Sarah Doyle 

occurred in the Navajo Sandstone (Jn), including the 

impressive 1983 rockfall at Rainbow Bridge National 

Monument (see GRI report by Graham 2009; Sarah 

Doyle, written communication, 4 May 2015). Rockfalls 

were also reported from the Chinle Formation (3), 

Entrada Sandstone (2), Wingate Sandstone (1), Kayenta 

Formation (1), and Morrison Formation (1). 

The Chinle Formation (TRc) is especially susceptible 

to slope movements because of its abundant bentonite 

content. The shrink-swell property of bentonite 

produces nearly impassable slippery roads and trails 

and slippery slopes that easily give way to landslides and 

slumps. 

Hiking on talus landslides (Qmt) may be potentially 

dangerous. Talus deposits may become dangerously 

unstable during periods of increased precipitation. 

Water tends to decrease friction and eventually the piles 

of talus begin to slide down slope.

Figure 36. Photograph of moqui marbles. These lose 

concretions on the surface of the friable Navajo 

Sandstone cover the trail to Horseshoe Bend Overlook 

and may lead to slippery conditions. Squares on 

scale bar are 1 cm to a side. National Park Service 

photograph.

Figure 37. Photograph of a cloud of dust from a rockfall. This rockfall occurred in the jointed Wingate Sandstone just 

east of Bald Rock Canyon near the crest of the Circle Cliffs anticline, San Juan Arm, Glen Canyon National Recreation 

Area. Photograph from Anderson et al. (2010, figure 21).
66

There are many options that park managers can 

consider to reduce risk associated with slope movement 

hazards. One is visitor and staff education regarding 

the potential risks. Verbal warnings by park rangers, or 

signs and other written notices posted at visitor centers, 

trailheads (fig. 35), and/or websites is one option to 

educate visitors. Another option is limiting access to 

potentially hazardous sites via fencing, ropes, or other 

barriers. These options should be assessed by NPS 

staff with regards to impacts to the natural experience, 

fiscal limitations, visitor access, and maintenance 

requirements.

One resource management tool that is expected to 

be completed in 2016 is a map folio consisting of 

nine or ten GIS-based geologic-hazard maps (Tyler 

Knudsen, Utah Geological Survey, geologist, written 

communication, 5 December 2015). The 1:24,000-scale 

maps will cover approximately 750 km2

 (290 mi2) near 

high-use areas at Wahweap/Lees Ferry and Bullfrog/

Hall’s Crossing. Each map will cover a different hazard 

including rockfall, landslides, flooding, faulting, and 

problematic soils. The mapped hazard will be ranked on 

a relative high, medium, or low index. 

If funding permits, resource managers could consider 

obtaining quantitative information to assess the 

frequency and magnitude of rockfall and other slope 

movements in high visitation areas. A photomonitoring 

program is one possibility. The Geoscientist-in-theParks program (http://go.nps.gov/gip) is an option to 

support such a project. The NPS Geologic Resources 

Division Photogrammetry website (http://go.nps.gov/

grd_photogrammetry) provides examples of how 

photographic techniques support structural analysis of 

rockfall areas.

In the Geological Monitoring chapter about slope 

movements, Wieczorek and Snyder (2009) described 

five vital signs for understanding and monitoring slope 

movements: (1) types of landslide, (2) landslide causes 

and triggers, (3) geologic materials in landslides, (4) 

measurement of landslide movement, and

(5) assessment of landslide hazards and risks. Additional 

information regarding slope movements, monitoring, 

and mitigation options may be found in Highland and 

Bobrowsky (2008) and the following websites: the US 

Geological Survey landslides website(http://landslides.

usgs.gov/), the NPS Geologic Resources Division 

Geohazards (http://go.nps.gov/geohazards), and the 

NPS slope movement monitoring website (http://

go.nps.gov/monitor_slopes).

Flash Floods and Debris Flows

During the summer monsoon season in southern Utah, 

intense thunderstorms cause flash floods and debris 

flows. Flash floods are common in this region of the 

Colorado Plateau because the arid, sparsely vegetated 

terrain does not have the capacity to absorb abundant 

precipitation that falls over a short time period. Runoff 

flows rapidly through the narrow slot canyons carved in 

the Kayenta Formation (Jk) and Navajo Sandstone (Jn). 

Even small storms can turn normally dry arroyos into 

raging torrents of water and mud in minutes.

Flash floods can transport clasts the size of boulders, 

along with vegetation and other debris, and these debris 

flows can quickly overwhelm hikers in slot canyons with 

little time to escape and no place to go. Fatal flash floods 

have occurred within the recreation area. 

Debris flows may originate kilometers away from the 

slot canyons in Glen Canyon National Recreation 

Area. For example, a fatal Antelope Canyon debris flow 

in 1997 originated from a cloudburst 24 km (15 mi) 

southeast of the canyon. At the trailhead, the skies were 

clear. National Park Service staff recommend that hikers 

seek weather information before hiking the slot canyons 

in the recreation area. The Glen Canyon National 

Recreation Area website provides safety information 

(https://www.nps.gov/glca/planyourvisit/safety.htm) 

and a podcast about flash floods (https://www.nps.

gov/glca/learn/photosmultimedia/podcasts.htm). The 

Grand Canyon National Park website(http://www.nps.

gov/grca/planyourvisit/weather-dangers.htm) provides 

a list of safety factors regarding hiking safely in canyon 

country and being aware of flash floods.

Floods can also damage or destroy park infrastructure. 

On September 12, 2013, flood waters washed out a 

newly paved road to Lees Ferry (fig. 38). According to 

park staff, the flood waters deposited a “VW-van-sized 

rock” in the center of the road (National Park Service 

2015f).

Flash floods also shape the landscape of Glen Canyon 

National Recreation Area. These natural processes form 

alluvial-fan deposits (Qaec) at the mouth of canyons 

where debris flow velocity dramatically decreases. 

Clasts in the alluvial fans may be as large as boulders.
67

Paleontological Resource Inventory, 

Monitoring, and Protection

All paleontological resources are nonrenewable and 

subject to science-informed inventory, monitoring, 

protection, and interpretation as outlined by the 

2009 Paleontological Resources Preservation Act (see 

Appendix B). As of June 2016, regulations associated 

with the Act were awaiting surnaming by the National 

Park Service (Julia Brunner, Policy and Regulatory 

Specialist, NPS Geologic Resources Division, written 

communication, 20 June 2016). The fossils of Glen 

Canyon National Recreation Area are diverse and 

significant. See “Paleontological Resources” section.

In 2009, Glen Canyon National Recreation Area was 

selected as the prototype Paleontological Monitoring 

Park for the National Park Service. According to the 

Glen Canyon National Recreation Area Foundation 

Document, approximately 350 paleontology sites have 

been located, but only about 10% of these sites have 

condition and trend assessments (National Park Service 

2014a). The Foundation Document identified the 

following challenges:

● Fluctuating lake levels (wetting and drying cycles) 

that may damage sites.

● Vandalism and illegal collecting, especially petrified 

wood in the Chinle Formation and fossils in easily 

accessible sites.

● Lack of staff or funds to survey and monitor sites.

● Effects from climate change, including severe 

flooding, storms, and accelerated erosion rates.

Fossils associated with the clay-rich Tropic Shale 

(Kt; table 8) have also been impacted by erosion 

and theft (Miller no date). These fossils are distinct 

Figure 38. Photograph of boulders and mud covering the road to Lees Ferry following the September 2013 flood. 

Person for scale. National Park Service photograph available at http://www.nps.gov/glca/learn/photosmultimedia/

photogallery.htm (accessed 30 April 2015).
68

paleontological resources, offering an insight into the 

organisms and environment of the Cretaceous Western 

Interior Seaway. Continued inventory, monitoring, and 

preservation are critical for maintaining this scientific 

resource and mitigating damage to these fossils.

Kirkland et al.’s (2010) Final Report for Paleontological 

Resources Inventory and Monitoring at Glen 

Canyon National Recreation Area recognized seven 

paleontological sites in Lockley’s Cove, an informal 

name for the recreation area’s first identified 

Paleontological Site Complex (PSC). A PSC is defined 

as “an area of restricted geographic and temporal 

extent that preserves an abundance of important fossil 

localities” (Kirkland et al. 2010, p. 28). Slick George’s 

Figure 39. Map of Slick George Dinosaur Tracksite, Glen Canyon National Recreation Area. (A) Distribution of dinosaur 

tracks showing the position of the reference stake and crack monitors for future site monitoring. (B) Overview of crack 

monitor 1 looking north. (C) Overview of crack monitor 2 looking east. Diagram and photographs from Kirkland et al. 

(2010, figure 23).
69

Dinosaur Tracksite, an exceptional tracksite within 

Lockley’s Cove PSC, was established as the first official 

monitoring site in Glen Canyon National Recreation 

Area (fig. 39). The site is about 8 m (26 ft) below the 

high waterline on the east side of Lake Powell. 

The 2010 report recommended specific monitoring 

protocol for the site and any future monitoring sites 

inventoried within the recreation area. This protocol 

included using NPS locality data forms, developing 

hard-copy “Paleontological Locality Files,” and 

developing a detailed monitoring database (Kirkland 

et al. 2010). Since 2010, the following significant 

developments have been made towards implementing 

these recommendations (John Spence, written 

communication, 9 December 2015):

● A GIS-rational database that contains site-specific 

spatial and scientific baseline data. The site 

information includes whatever was available and 

may range from a simple location to more detailed 

information about monitoring and significance, 

photos, and any additional information.

● Hard-copy files that include assessment and 

monitoring forms. These are kept for all sites and 

include any information based on site visits and 

monitoring.

● On-going training of personnel who monitor sites.

● Systematic files for many, but not all, 

paleontological sites. Files on the majority of older 

sites may contain only basic information, such as 

location and fossil type.

Santucci et al. (2009) present a guide to collecting and 

recording monitoring site data, especially important 

indicators, or “Vital Signs.” Kirkland et al. (2010) 

identified critical data that applied to the following Vital 

Signs.

● Vital Sign 1—Rates of Natural Erosion I (Geologic 

Variables). Erosion measurements using calibrated 

stakes and repeat photography of pre-determined 

reference points. 

● Vital Sign 2—Rates of Natural Erosion II (Climatic 

Variables). Measuring short- and long-term effects 

of climatic fluctuations and their impact on fossil 

resources by noting new cracks or widening of old 

cracks due to freeze-thaw cycles; new vegetation 

growing in cracks; encroaching vegetation or roots; 

proliferation of lichen or algae; spalling of rock; and 

evidence of secondary mineral encrustation that 

obscures or obliterates the fossil.

● Vital Sign 3— “Catastrophic” Geologic Processes or 

Geohazards. Documenting slope movements that 

may cover or expose fossil sites.

● Vital Sign 4—Hydrology and Bathymetry. 

Documenting the spatial relationship of fossil sites 

with lake levels of Lake Powell, groundwater seeps, 

and wave action. Also, documenting the association 

of fossil sites with tufa deposits.

● Vital Sign 5—Human Impacts. Monitoring adverse 

human impacts on fossil resources by recording 

a fossil site’s proximity to roads, trails, shoreline, 

marines, beaches, fire circles, old anchors, trash, 

and toilet paper. Also, documenting footprints 

and trampling, whether by humans or wild or 

domestic animals. Monitoring vandalism and theft 

by documenting stacked piles of petrified wood or 

body fossils and slabs of tracks turned on end.

Many of the fossil localities identified in the recreation 

area were submerged as lake levels rose. In the course 

of their research, Kirkland et al. (2010) found a number 

of new sites. Developing an inventory of fossil sites will 

be an ongoing process. Each of the documented sites 

at Glen Canyon National Recreation Area will need to 

be evaluated to determine the frequency and nature of 

future monitoring (Kirkland et al. 2010).

As suggested by Kirkland et al. (2010), resource 

managers may wish to implement protocols previously 

developed by Milner et al. (2006), Spears et al. (2009), 

and Santucci et al. (2009). Some of the methods in these 

references include:

● Repeat photography using recognizable natural or 

human-made landmarks (e.g., stakes).

● Using stakes (rebar) to provide reference points.

● Developing site-specific data packets for site 

monitors.

● Careful documentation of field notes and 

observations.

● Mapping and photogrammetric documentation 

of select sites (labor intensive and requires special 

techniques).

● Monitoring cracks in the rock by using clear resin 

plates following the technique used at Dinosaur 

National Monument.

● Sampling rocks to determine the effect of water on 

the rock’s minerals, mineral cement, and changes, if 

any, in the rock’s porosity and permeability.
70

Obviously, developing a detailed inventory and 

systematically monitoring the paleontological 

resources at Glen Canyon National Recreation Area 

will be a substantial undertaking. To develop a proper 

paleontological database for Glen Canyon National 

Recreation Area, previous fieldwork conducted by 

other institutions, such as the Museum of Northern 

Arizona, Denver Museum of Nature and Science, 

and the US Geological Survey, should be assembled 

and checked for duplication or omission of site data, 

although locating sites from old field data may prove 

problematic (Kirkland et al. 2010). Hard-copy data need 

to be maintained in digital form for use in the field. Each 

identified fossil locality needs to be visited to determine 

if the site is “at risk” and should be monitored. 

Protocols, methodology, and schedules for monitoring 

each site need to be formalized. Paleontological 

sensitivity maps could be made that include fossiliferous 

formations and members that are susceptible to 

chemical weathering, dissolution, spalling, wave action, 

and human activity.

In addition, Glen Canyon National Recreation 

Area can support ongoing research and educational 

opportunities related to paleontological resources 

(National Park Service 2014a). To survey the expanse 

of the recreation area, cooperative relationships 

should be developed with the Utah Geological Survey 

and other research groups with paleontological 

expertise. According to the Foundation Document, an 

interdisciplinary team consisting of personnel from 

Visitor and Resource Protection, Science and Resource 

Management, and Interpretation and Education could 

be assembled to monitor, conserve, and interpret 

paleontological sites (National Park Service 2014a). A 

paleontologist position shared among Glen Canyon 

National Recreation Area, other national parks, and 

Grand Staircase-Escalante National Monument is one 

possibility (John Spence, written communication, 9 

December 2015).

Cave and Alcove Management

Cave features are non-renewable resources. The Federal 

Cave Resources Protection Act of 1988 requires the 

identification of “significant caves” in NPS areas, the 

regulation or restriction of use as needed to protect 

cave resources, and inclusion of significant caves in 

land management planning. The act also imposes 

penalties for harming a cave or cave resources and 

exempts park managers from releasing specific location 

information for significant caves in response to a FOIA 

request (see also Appendix B). A park-specific cave 

management plan has not yet been completed for Glen 

Canyon National Recreation Area. Such plans include 

a comprehensive evaluation of current and potential 

visitor use and activities, as well as a plan to study 

known and discover new caves. The NPS Geologic 

Resources Division can facilitate the development of 

such a plan.

The caves and alcoves listed in table 9 contain a diverse 

assemblage of paleontological and cultural resources 

that the park currently manages. Research of the thick 

organic layer in Bechan Cave began in 1983, and it is 

the only cave from which skeletal evidence of a large 

mammal was discovered (a tooth from the shrubox 

Euceratherium collinum, see table 9) (Santucci et 

al. 2001). Oakleaf Alcove was the site of numerous 

archaeological excavations in the 1960s, but it was 

submerged under Lake Powell in 2001 (Santucci et al. 

2001). Prior to its submergence, Oakleaf Alcove had 

been vandalized. 

In the Geological Monitoring chapter about caves 

and associated landscapes, Toomey (2009) described 

methods for inventorying and monitoring caverelated vital signs, including the following: (1) cave 

meteorology, such as microclimate and air composition; 

(2) airborne sedimentation, including dust and lint; 

(3) direct visitor impacts, such as breakage of cave 

formations, trail use in caves, graffiti, and artificial cave 

lighting; (4) permanent or seasonal ice; (5) cave drip and 

pool water, including drip locations, rate, volume, and 

water chemistry, pool microbiology, and temperature; 

(6) cave microbiology; (7) stability issues associated with 

breakdown, rockfall, and partings; (8) mineral growth 

of speleothems, such as stalagmites and stalactites; 

(9) surface expressions and processes that link the 

surface and the cave environment, including springs, 

sinkholes, and cracks; (10) regional groundwater levels 

and quantity; and (11) fluvial processes, including 

underground streams and rivers.

Sediment Deposition in Lake Powell

Lake Powell is, of course, one of the fundamental 

resources in the recreation area (National Park Service 

2014a). Reservoirs, however, are temporary and 

eventually fill with sediment. Abundant sediment enters 

Lake Powell from the Colorado River, one of the most 

sediment-laden rivers in North America, and sediment 
71

accumulation, along with low water levels, has impacted 

several locations in the lake. Visitor access to Hite 

marina, for example, has been lost due to low water 

levels and the growth of the Hite delta. The absolute 

minimum usable elevation at the Hite marina is 1,111 m 

(3,645 ft) above sea level, which has not been reached 

since 2001 (Lake Powell Water Database 2016). 

Climate change models predict higher temperatures, 

decreased precipitation, and decreased runoff by 

10%–30% by 2100 (see “Potential Impacts from Global 

Climate Change” section; National Park Service 2014a). 

As lake levels lower, continued sedimentation into the 

lake will reduce storage in Lake Powell, potentially by 

50% by 2021. Currently, silt accumulates behind the 

dam and fills the reservoir at an average rate of 0.046 

km3 (0.011 mi3) per year. As lake levels fluctuate and 

sedimentation eliminates or complicates access to 

locations within the recreation area, resource managers 

will need an updated strategy to provide and maintain 

visitor and commercial access (National Park Service 

2014a). 

Abandoned Mineral Lands and Potential 

Mining Activity

Abandoned mineral lands (AML) are lands, waters, 

and surrounding watersheds that contain facilities, 

structures, improvements, and disturbances associated 

with past mineral exploration, extraction, processing, 

and transportation, including oil and gas features 

and operations. The NPS takes action under various 

authorities to mitigate, reclaim, or restore AML in order 

to reduce hazards and impacts to resources. 

According to the NPS AML database (updated 28 

October 2014) and Burghardt et al. (2014), Glen Canyon 

National Recreation Area contains 99 AML features at 

39 sites. Features at the sites include mine adits, waste 

rock, abandoned oil and gas wells, surface mines, 

abandoned mining equipment, buildings, and roads. 

Features that require mitigation are associated with the 

abandoned Jomac and El Pequito underground mines. 

As mentioned in the “Uranium Mining” section, high 

levels of radiation may require additional monitoring 

and mitigation of some AML features as documented in 

the database.

Sixteen of the sites are abandoned oil and gas wells. 

Nine of the sites are associated with the five abandoned 

underground uranium mines mentioned in the 

“Uranium Mining” section. Six of the sites are surface 

mines. The remaining sites include a placer mine, and 

abandoned access roads.

As Burghardt et al. (2014) discuss, AML features 

pose a variety of resource management issues such 

as visitor and staff safety and environmental quality 

of air, water, and soil. AML features can also provide 

habitat for bats and other animals, some of which may 

be protected under the Endangered Species Act or state 

species listings. Resource managers at Glen Canyon 

National Recreation Area inventory and report on the 

AML features in the park. Data should be recorded 

in the Servicewide AML Database (the NPS Geologic 

Resources Division may be able to provide assistance). 

The NPS AML website, http://go.nps.gov/aml, provides 

further information.

Mineral Leasing

Generally, units of the National Park System are not 

open to federal mineral leasing under the Mineral 

Leasing Act (30 USC § 181 et seq.) and the Mineral 

Leasing Act for Acquired Lands (30 USC § 351 et seq.). 

However, Glen Canyon National Recreation Area is 

one of three units in the National Park System which 

has specific statutory authority to allow federal mineral 

leasing. See also NPS Management Policies 2006 § 8.7.2 

and Appendix B. The Glen Canyon enabling legislation 

authorizes the removal of nonleasable or leasable 

minerals in accordance with BLM regulations at 43 CFR 

Part 3109.2, only if mineral removal does not have a 

significant adverse effect on the administration of the 

unit.

Approximately 32,000 ha (80,000 ac) in Glen Canyon 

National Recreation Area are designated as the “Special 

Tar Sands Area (STSA)” (see “Tar Sands Exploration” 

section).

Uranium Mining

Mining for uranium occurred mostly in the 1950s 

through 1970s, but only sporadic, small operations 

were conducted within or near what is now Glen 

Canyon National Recreation Area. Uranium mine 

openings at the following four abandoned uranium 

mine adits have been closed to prevent public access 

and to reduce health and safety risks: Jomac Mine, 

Blue Notch, White Canyon, and Whirlwind. In 1992, 

three adits in the Monitor Butte Member (TRcmn) of 

the Chinle Formation at the Jomac Mine were sealed, 

but routine monitoring in 2008 discovered the backfill 
72

had been breached. Portals to adits were patched and 

again backfilled (fig. 40). The adits at the Jomac Mine 

will receive additional attention in 2016 (John Spence, 

written communication, 9 December 2015). Adits 

from White Canyon, Blue Notch, and Whirlwind were 

backfilled in 2002 and 2003. 

Waste rock from mining operations at the White 

Canyon, Blue Notch, and Whirlwind mines do not 

pose a potential hazard. However, ore piles associated 

with the abandoned Jomac Mine are considered a high 

radiation risk and may require remediation. 

Removal or encapsulation of the spoils piles has 

not been done at these abandoned sites because 

radiation exposure to reclamation crews could be 

much greater than the inconsequential exposure to 

occasional visitors passing by the sites. Furthermore, 

far more contamination would be released into the 

environment in any type of reclamation attempt than 

if the piles were left alone in their current condition. 

Detailed site investigations conducted by the National 

Park Service in collaboration with US Environmental 

Protection Agency and the State of Utah on similar 

abandoned uranium sites in Canyonlands and Capitol 

Reef National Parks showed that there is virtually no 

environmental signature of uranium mining much 

beyond 10 m (30 ft) from the sampled waste rock piles, 

at which point radionuclide and heavy metals values 

return to essentially background levels. (John Burghardt 

and Phil Cloues, Geologic Resources Division, 

geologists, personal communications 19 April 2005).

In October, 2015, the recreation area finished the 

evaluation of the El Pequito mine. In 2016, the main 

entrance of the El Pequito mine will be closed (John 

Spence, written communication, 9 December 2015).

Coal Mining

In the early 1900s, Charles H. Spencer’s American 

Placer Company began mining for gold near Lees Ferry, 

and Spencer needed coal to run his equipment. The 

nearest coal seam was 45 km (28 mi) upstream in Warm 

Creek. Initially, Spencer built a trail and used mules to 

haul the coal. Finding mules to be inefficient, Spencer 

built a 28-m (92-ft) steamboat, named the Charles H. 

Spencer, in 1912. The steamboat used most of the coal it 

transported, and by the end of 1912, Spencer’s investors 

had pulled out. Spencer left the area and the Charles H. 

Spencer sank to the bottom of the Colorado River. The 

Figure 40. Photographs of mitigation work at the Jomac 

Mine, Glen Canyon National Recreation Area. Top: Native 

rock and masonry are used to seal the adit. Bottom: 

Backfill in progress at the mine entrance using the mine’s 

waste rock. National Park Service photographs from 

Burghardt et al. (2014, figure 11).
73

steamboat is now on the National Register of Historic 

Places. The Spencer mine was small, and in 1993, five 

adits were backfilled (Geologic Resources Division 

AML database). The Spencer Trail remains today, with 

its trailhead near the launch ramp for the Colorado 

River at Lees Ferry.

Unlike other federal minerals (see “Mineral Leasing”), 

coal leases cannot be issued in Glen Canyon National 

Recreation Area, or any other area of the National Park 

System, under the Federal Coal Leasing Amendments 

Act of 1975 (30 USC § 201). Likewise the Surface 

Mining Control and Reclamation Act of 1977 (SMCRA; 

30 USC § 1201 et. seq.) prohibits surface coal mining 

operations on any lands within the boundaries of a NPS 

unit, subject to valid existing rights. See Appendix B.

Under SMCRA Section 522(e), the NPS also has a 

role in surface coal mine operations outside park 

boundaries. If NPS can show that an operation will 

adversely affect park resources, then the NPS becomes 

a joint permitting agency with the appropriate lead 

agency (Office of Surface Mining Reclamation and 

Enforcement (OSMRE) or state agency). The NPS 

can then require mitigation measures designed to 

reduce the impacts to park resources or if mitigation 

measures cannot be sufficiently designed to avoid those 

impacts, the NPS can decline to approve the operation’s 

permit. Another alternative is for the NPS and/or other 

interested parties to petition OSMRE to declare the 

lands proposed for the surface mine unsuitable for 

surface coal mining.

Burning Coal Beds

Strata containing coal, such as the coal beds in the John 

Henry Member of the Straight Cliffs Formation (Ksj) 

and discontinuous seams in the Dakota Sandstone 

(Kd), can spontaneously combust. Participants at the 

1999 scoping workshop for Glen Canyon National 

Recreation Area and Rainbow Bridge National 

Monument noted that burning coal beds may occur in 

the recreation area (NPS Geologic Resources Division 

and Natural Resources Information Division 1999). 

However, the only burning coal beds in the region occur 

in Grand Staircase-Escalante National Monument, and 

they do not impact Glen Canyon National Recreation 

Area (John Spence, written communication, 9 

December 2015).

Oil and Gas Exploration

The National Park Service works with adjacent land 

managers and other permitting entities to help ensure 

that National Park System resources and values are not 

adversely impacted by external mineral exploration and 

development. Potential impacts include groundwater 

and surface water contamination, erosion and siltation, 

introduction of exotic plant species, reduction of 

wildlife habitat, impairment of viewsheds and night 

skies, excessive noise, and diminished air quality. Visitor 

safety and overall degradation of the visitor experience 

are particular concerns. The NPS Geologic Resources 

Division Energy and Minerals website,

http://go.nps.gov/grd_energyminerals, provides 

additional information.

In 1969, a petroleum exploration company acquired the 

rights to explore for petroleum on 3,940 ha (9.730 ac) 

in southern Utah. At that time, the BLM administered 

the land. Some of this land is now part of either Glen 

Canyon National Recreation Area or Capitol Reef 

National Park. In 1990, the company submitted an 

application to drill an exploratory well in the Circle 

Cliffs area in Glen Canyon National Recreation Area. 

Exploratory wells had previously been drilled on 

the Circle Cliffs in 1921 and 1947. Those wells were 

eventually plugged and abandoned. The company’s 

lease expired in 2007 prior to any drilling (National 

Park Service 2015g).

Most of the oil and gas in Utah is concentrated in 

Duchesne and Uintah Counties in the north and San 

Juan County in the south (Vanden Berg 2011). San Juan 

County produces 15.8% of Utah’s crude oil, primarily 

from the Greater Aneth oil field in the southeastern 

corner of Utah approximately 65 km (41 mi) from the 

eastern end of the San Juan Arm. The Greater Aneth 

oil field, discovered in 1956, is a giant oil field that 

originally contained an estimated 1.5 billion barrels of 

oil in place. As of 2012, 430 million barrels of oil had 

been produced primarily from the shallow marine 

limestone and dolomite in the Pennsylvanian Paradox 

Formation (PNp). This volume accounts for about 30% 

of the field’s estimated recoverable oil (Resolute Energy 

Corporation 2013; Utah Geological Survey 2013). 

Other potential hydrocarbon reservoirs in southeastern 

Utah include the beach and deltaic sandstones in the 

Pennsylvanian Honaker Trail Formation (PNht) and the 

eolian sandstones of the Permian Coconino Sandstone 

(Pco) (Utah Geological Survey 2013).
74

Tar Sands Exploration

About 130 km2 (50 mi2) of land in the Book Cliffs, north 

of Glen Canyon National Recreation Area, has been 

leased for tar sand production. An estimated 180 million 

barrels of oil could be produced from what would be 

the first tar sands mine in the United States (Fessenden 

2015; McCombs 2015).

Approximately 32,000 ha (80,000 ac) in Glen Canyon 

National Recreation Area are designated as the “Special 

Tar Sands Area (STSA).” Any new leases in the STSA are 

issued as combined hydrocarbon leases because of the 

Combined Hydrocarbon Leasing Act of 1981 (30 USC 

§ 181), which provided for the conversion of existing oil 

and gas leases and oil and gas mining claims in the STSA 

to combined hydrocarbon leases.

Tar sand mining presents a direct threat to air and 

water quality, as well as an impact to the viewshed. 

The permitted mine site lies within the upper reaches 

of the Colorado River watershed. Any contaminants 

may eventually be transported to Lake Powell and to 

water users in the lower Colorado River basin. Utah 

officials have approved three more tar sands operations 

in the same area. In the recent past, Utah officials have 

attempted to exchange state lands for potentially more 

economically productive federal lands, and similar 

attempts could potentially occur in the Tar Sand 

Triangle. 

Development of White Rim Sandstone (Pwr) tar sand 

deposits in the Tar Sand Triangle faces the following 

hurdles that will make commercial bitumen recovery 

difficult and expensive, but not impossible (Vanden 

Berg 2011; Schamel 2013):

● Low oil saturations and low quality of bitumen.

● High sulfur content of the oil and high viscosity at 

reservoir temperatures.

● Difficult access over unimproved roads, all of which 

pass through Glen Canyon National Recreation 

Area.

● Potentially expensive access to water.

● Lack of infrastructure, including petroleum service 

vendors and other support services in southeast 

Utah.

● Problems with reservoir sand heterogeneity.

● Proximity of environmentally protected public 

lands containing exceptional landscapes.

The Combined Hydrocarbon Leasing Act specifies that 

the conversion of leases within National Park Service 

units is prohibited without a finding by the Secretary 

of the Interior that there would be no significant 

adverse impacts. Draft Environmental Impact 

Statements (DEISs) completed in the 1980s for the 

Tar Sand Triangle and Circle Cliffs deposits discussed 

the adverse environmental impacts that would result 

from developing tar sands in Utah (Baxter 2008). The 

same environmental, economic, socio-economic, and 

technical concerns that existed in the 1980s exist today 

(Baxter 2008). 

Impacts from External Mining Activities

The accidental spill of contaminated water from 

the Gold King Mine near Silverton, Colorado, on 5 

August 2015 highlighted the potential impacts of past 

and present mining activities on Lake Powell and 

the Colorado River watershed. As many as 3 million 

gallons of wastewater contaminated with heavy metals, 

including arsenic, cadmium, lead, and mercury, were 

released into a tributary to the Animas River, which 

flows into the San Juan River. These rivers are part of 

the upper Colorado River basin watershed and supply 

water for drinking, recreation, livestock, and irrigation 

in Colorado, New Mexico, and Utah. 

By mid-August 2015, the contaminated water had 

flowed into Lake Powell, but the Environmental 

Protection Agency (EPA) did not expect any significant 

impacts to the lake (Romboy 2015). According 

to Richard Hepworth, state Division of Wildlife 

Resources aquatics manager in southern Utah, much 

of the contamination dissipated before reaching Lake 

Powell. Storms and runoff events may transport the 

contaminants into the lake in the future. Wildlife 

resource managers already check Lake Powell fish for 

mercury and will now test for other heavy metals, as 

well. 

Heavy metal contamination, however, is not new to the 

surface waters in Glen Canyon National Recreation 

Area. In 1994, the Water Resources Division of the 

National Park Service conducted a baseline water 

quality inventory for the recreation area and found that 

several heavy metals exceeded their respective EPA 

water quality criteria at least once within the study area. 

Arsenic, cadmium, chromium, copper, lead, silver, zinc, 

selenium, and mercury exceeded the acute or chronic 

criteria for the protection of freshwater aquatic life, and 
75

arsenic, cadmium, chromium, lead, nickel, mercury, 

and natural uranium exceeded the EPA drinking water 

criteria (Water Resources Division 1994).

At least twelve Superfund sites exist in the Colorado 

Rocky Mountains, and eight of these have been 

identified as among the 79 most polluted sites in the 

country (Environmental Protection Agency 2015). 

The Gold King Mine is one of the mines identified 

within the Upper Animas Mining District. Soil and 

water contamination at many of these sites is being 

successfully addressed by the combined efforts of 

the local communities and the EPA. In contrast, the 

Silverton community in the 1990s elected to decline 

the EPA’s help to construct an on-site water treatment 

plant, so the EPA agreed to postpone adding the Gold 

King Mine to the Superfund National Priorities List. 

However, the community-based efforts to remediate 

contamination to the Animas River began to fail in 2005 

when water quality began to significantly decrease in the 

river (Environmental Protection Agency 2015). 

The closed mine sites also include potential uranium 

contamination from the Uravan Uranium Project near 

Montrose, Colorado. Uranium mining is part of the 

rich mining history of Utah. In southeastern Utah, 

the number of abandoned uranium mines on BLM 

land ranges from 8,000 to 11,000, including those 

within Glen Canyon National Recreation Area (BLM 

2015). These abandoned uranium mines are within 

the Colorado River watershed, and their waste dumps 

often contain elevated levels of heavy metals, such 

as cadmium, lead, arsenic, and zinc. An estimated 

5%–10% of the abandoned mine sites may have water 

quality problems (BLM 2015).

With uranium prices increasing, a new uranium mining 

boom is occurring in Utah (BLM 2015). Hard-rock 

mining for gold and other precious metals continues in 

Colorado. The prospect of tar sand mining in Utah adds 

an additional external threat to the water quality in Glen 

Canyon National Recreation Area.

Potential Impacts from Global Climate 

Change

As climate continues to change, national parks 

across the country, including Glen Canyon National 

Recreation Area, will face many challenges. The 

NPS Climate Change website, http://go.nps.gov/

climatechange, provides background information 

and NPS context and actions. Primary concerns for 

the national recreation area include lower amounts 

of precipitation which will affect water availability for 

users of water stored in Lake Powell, as well as waterdependent ecosystems such as hanging gardens. 

On the Colorado Plateau, elevation strongly controls 

temperature, precipitation and evapotranspiration 

(Spence 2001). In general, precipitation increases 

and potential evaporation decreases as elevation 

increases. The arid-humid climate boundary occurs 

at approximately 2,730 m (8,957 ft) (Spence 2001). 

The Glen Canyon region includes some of the lowest 

elevations on the Colorado Plateau and some of the 

highest temperatures. Elevations along the Colorado 

River range from 1,219 m (4,000 ft) at Moab to 978 

m (3,209 ft) at Lees Ferry, a drop of only 241 m (791 

ft) in 450 km (276 mi). The hot, arid climate at the 

elevation of Lake Powell accounts for an average annual 

evaporation of 2.6% of the lake’s volume, or roughly 0.8 

km3 (0.2 mi3) of water. 

Over an 82-year period (1916–1998), the average 

annual temperature at Lees Ferry was 16.9°C (62.4°F). 

In contrast, the average annual temperature at Bryce 

Canyon National Park, where the weather station 

is 2,412 m (7,914 ft) above sea level, was 5.1°C 

(41.2°F) through the second half of the twentieth 

century (Spence 2001). The yearly average potential 

evapotranspiration at Lees Ferry was 99.3 cm (39.1 in) 

over the same period, approximately double the average 

annual evapotranspiration at Bryce Canyon National 

Park.

Glen Canyon National Recreation Area lies in a rain 

shadow. Rainfall is reduced because of the high Wasatch 

and Kaibab Plateaus to the north, west, and southwest. 

Over the 82-year period from 1916 to 1998, Lees Ferry 

received an annual average precipitation of 15.3 cm (6.0 

in) (Spence 2001). For comparison, Phoenix receives an 

average of 20.4 cm (8.04 in) of annual rainfall. 

Dynamic weather patterns in the region fluctuate 

between cool wet phases and dry warm phases based 

on the 20-year cyclic Pacific Decadal Oscillation (PDO), 

the Atlantic Multi-decadal Oscillation (AMO), which 

has a 50–80 year cycle, and El Niño-La Niña (EL-LN) 

events. The 1983 flood that almost overtopped Glen 

Canyon Dam, for example, corresponded to the 1983 El 

Niño event (National Park Service 2007). The extremely 

complex interactions between the PDO, AMO, and ELLN are not well understood, but these interactions have 
76

a significant effect on the region’s water supply and the 

organisms that depend on this water supply.

Water Resources

In general, precipitation is projected to decrease 

in the southwestern United States, and drought 

and increased warming are predicted to increase 

competition among agricultural, municipal, industrial, 

and ecological uses for scarce water resources, which 

are already overallocated (Bates et al. 2008; Karl et al. 

2009; Intergovernmental Panel on Climate Change 

2014; Melillo et al. 2014). Already known for its 

mega-droughts, the Southwest is expected to sustain 

substantially hotter droughts that will become more 

frequent, intense, and longer lasting than historical 

droughts in the Colorado River Basin (Karl et al. 2009; 

Intergovernmental Panel on Climate Change 2014; 

Melillo et al. 2014; Cook et al. 2015). Demand for 

freshwater may impact Lake Powell lake levels.

Over the past century, the duration and extent of 

snow cover, mountain snow equivalent, and annual 

precipitation has decreased in the southwestern US, 

and winter and spring precipitation is predicted to 

decrease even further by 2100, although a trend towards 

a slight increase in winter precipitation on the Colorado 

Plateau has occurred over the last 30–40 years (Spence 

2001; Bates et al. 2008; Melillo et al. 2014). There has 

also been a shift toward earlier peak runoff because 

more precipitation is falling as rain rather than snow 

(Knowles et al. 2006; Loehman 2009). In addition, dust 

and soot transported by winds from lowland regions 

will accumulate on the surface of snowpack, increasing 

the amount of the sun’s energy absorbed by the snow 

and resulting in an earlier snowmelt and evaporation. 

Already lower than 20th century average flows, 

streamflow in the Colorado River basin is projected to 

decline because of decreased snowpack and subsequent 

reduced spring runoff and soil moisture (Bates et al. 

2008; Intergovernmental Panel on Climate Change 

2014; Melillo et al. 2014).

At Lees Ferry, the minimum average temperature 

has significantly increased since 1944, although no 

significant changes have affected the average annual 

or maximum temperatures (Spence 2001). Increasing 

temperatures, even with no or minor changes in 

precipitation, will increase the rates of potential 

evapotranspiration in the Glen Canyon National 

Recreation Area (Spence 2001). Considering the 

general trend of increasing temperature at Lees Ferry, 

the annual potential evapotranspiration rate will 

increase from 99.3 cm (39.1 in) to 113.6 cm (44.8 in). By 

comparison, the potential evapotranspiration rate from 

1982–2005 for Tucson in the Sonoran Desert averaged 

110.0 cm/year (43.3 in/yr).

Ecosystems and irrigation demands are projected 

to be significantly stressed due to a combination of 

climate change, growing water demand, and water 

transfers to urban and industrial users (Bates et al. 

2008; International Panel on Climate Change 2014). 

Increased minimum temperatures at lower elevations 

may encourage the growth of cool season plants 

and the subsequent depletion of soil moisture prior 

to the germination of warm season species (Spence 

2001). Long-term models predict that grasslands and 

woodlands will increase on the Colorado Plateau at the 

expense of arid scrub vegetation.

Hundreds of reservoirs, irrigation projects and 

groundwater withdrawals have been developed in 

the semi-arid Colorado River basin in order to supply 

freshwater to a westward expanding population. The 

Colorado River Compact, negotiated in the 1920s, 

allocated the Colorado River’s water to seven US states, 

two Mexican states, and thirty-four American Indian 

tribes. However, the water was allocated based on the 

wettest period in over 400 years (Pulwarty et al. 2005; 

Bates et al. 2008; Karl et al. 2009). About 30–40% of 

the region has been under severe drought conditions 

since 1999, and the flow of the Colorado River was 

at a 5-year low from 2000 to 2004 (Bates et al. 2008). 

With increased population growth, increased climatic 

warming, increased evaporation, increased surface and 

groundwater withdrawals, and decreased runoff, the 

Colorado River Compact may meet its requirements 

only 60–75% of the time by 2025 (Christensen et al. 

2004). Discharge of the Colorado River at Lees Ferry, 

which separates the upper from the lower Colorado 

River basin, may be insufficient to meet current water 

demands within 20 years (Pulwarty et al. 2005; Bates et 

al. 2008).

In addition, hydropower production is predicted to 

decrease as total runoff decreases within the Colorado 

River basin (Christensen et al. 2004; Bates et al. 

2008). Changes in precipitation and river discharge 

significantly affect hydroelectric generation. For 

example, a 1% decrease in streamflow in the Colorado 
77

River basin results in a 3% drop in power generation 

(Karl et al. 2009). 

Increasing development and climate variability may 

intensify conflicts among water users in the Colorado 

River basin. Lake Powell levels may continue to decline 

in order to meet the needs of the Colorado River 

Compact. Declining lake levels may impact recreational 

activities and expose fossil sites to erosion. Increased 

erosion from wave activity in Lake Powell and flash 

floods in tributary streams and slot canyons will 

increase the amount of silt deposited in the reservoir, 

as well. Climate change will not only impact average 

conditions but also accelerate specific climatic events 

such as intense storms, floods, and drought. These 

extreme events can significantly cause fundamental and 

widespread shifts in the condition of park resources 

(National Park Service 2014b).

Hanging Gardens

Hanging gardens and other spring systems in Glen 

Canyon National Recreation Area and throughout 

the Colorado Plateau are fragile ecosystems (fig. 9). 

In addition to foot traffic, livestock, and the invasion 

of exotic species that already threaten the delicate 

vegetation in the hanging gardens, global climate 

warming threatens the hanging gardens in Glen Canyon 

National Recreation Area (National Park Service 

2015c).

If precipitation decreases and groundwater levels lower, 

seeps and springs along the contact of the Kayenta 

Formation (Jk) and the Navajo Sandstone (Jn) may also 

decrease. Many animals and plants living in the hanging 

gardens depend on this water for survival. Global 

climate change may significantly jeopardize the water 

resources and survival of organisms that are dependent 

Figure 41. Map of earthquake probability for Glen Canyon National Recreation Area. The map shows the probability of 

an earthquake with a magnitude >5.0 occurring within 100 years. Brown lines are fault traces. Blue lines are rivers. The 

black outline is the approximate extent of Lake Powell. Map created using the US Geological Survey 2009 Earthquake 

Probability Mapping tool, available at http://geohazards.usgs.gov/eqprob/2009/index.php (accessed 29 June 2016).
78

on the hanging gardens in Glen Canyon National 

Recreation Area (National Park Service 2007).

Earthquakes

Earthquakes are ground vibrations—shaking—that 

occur when rocks suddenly move along a fault, 

releasing accumulated energy (Braile 2009). Earthquake 

intensity ranges from imperceptible by humans to 

total destruction of developed areas and alteration 

of the landscape. Earthquakes can directly damage 

park infrastructure, or trigger other hazards such as 

slope movements that may impact park resources, 

infrastructure, or visitor safety. 

Until 1979, earthquakes were measured using the 

Richter magnitude scale which is based on a logarithmic 

scale from 1 to 10. Seismologists now measure 

earthquake magnitude using the moment magnitude 

(energy released) scale, which is more precise than 

the Richter scale but retains the same continuum of 

magnitude values. The Modified Mercalli Intensity 

Scale is a measure of the effect of an earthquake on 

Earth’s surface. It consists of a series of key responses 

such as sleeping people awakening, furniture moving, 

chimneys damaged, and finally, total destruction. 

All of Utah’s earthquakes are associated with Basinand-Range Province extension (Grant Willis, Utah 

Geological Survey, geologist, written communication, 

2 December 2015). Extension began about 17 million 

years ago and continues today. The Hurricane fault, 

west of Zion National Park, marks the eastern boundary 

of the Basin-and-Range Province, but the Paunsaugunt 

fault, which is responsible for the cliffs of Bryce 

Canyon National Park, is a potentially active fault in 

the transition zone between the Basin-and-Range and 

the Colorado Plateau. The Paunsaugunt fault is only 

about 56 km (35 mi) away from Glen Canyon National 

Recreation Area, and the even more active Sevier fault, 

west of Kanab, is only about 97 km (60 mi) away.

Since 1973, no earthquakes of magnitude 4.5 or greater 

have occurred in southeastern Utah (US Geological 

Survey 2014). Nevertheless, the probability that an 

earthquake of magnitude >5 (considered a “moderate” 

earthquake) will occur in the Glen Canyon National 

Recreation Area in the next 100 years ranges from 

0.04 to 0.30 (fig. 41; US Geological Survey 2010). 

The southern part of the recreation area where Glen 

Canyon Dam is located has a higher probability of an 

earthquake of this magnitude than does the area north 

of the San Juan Arm (fig. 41).

In the Geological Monitoring chapter about earthquakes 

and seismic activity, Braile (2009) described the 

following methods and vital signs for understanding 

earthquakes and monitoring seismic activity:

(1) monitoring earthquakes, (2) analysis and statistics 

of earthquake activity, (3) analysis of historical and 

prehistoric earthquake activity, (4) earthquake risk 

estimation, (5) geodetic monitoring and ground 

deformation, and (6) geomorphic and geologic 

indications of active tectonics. Braile (2009), the NPS 

Geologic Resources Division Seismic Monitoring 

website (http://go.nps.gov/seismic_monitoring), 

and the US Geological Survey Earthquakes Hazards 

website (http://earthquake.usgs.gov/), provide more 

information. The University of Utah Seismograph 

Stations (UUSS) provides real-time data and maps of 

the most recent earthquakes (http://quake.utah.edu/

index.shtml). 

Glen Canyon Dam and Downstream Impacts 

to the Colorado River

Typical of all large dams and their reservoirs, Glen 

Canyon Dam has trapped upstream sediment and 

significantly altered downstream flow regimes. Since 

the dam closed in 1963, average peak flows in Glen 

Canyon have decreased by 63% and the fine sediment 

supply has been essentially eliminated. The average 

daily legal range of outflow from Glen Canyon Dam 

is 140–570 m3/s (5,000–20,000 ft3/s), but flood events 

have produced a maximum flow of 9,120 m3/s (322,000 

ft3/s) (Anderson et al. 2010). After the dam closed, the 

downstream Colorado River channel narrowed and 

was transformed from a sand-dominated channel to a 

gravel-dominated river channel. Bed incision, which 

occurred primarily in 1965, has scoured an average 

of 2.6 m (8. 5 ft) of sediment from the center of the 

channel. Sandbars and pre-dam flood deposits have 

been eroded and once active sand and gravel bars have 

been abandoned and stabilized by vegetation (Grams et 

al. 2005, 2007, 2010). On the enclosed map, thin point 

bars consisting of alluvial deposits (Qal1) have formed 

at meander bends along the downstream reach of the 

Colorado River south of the Glen Canyon Dam.

The physical changes to the Colorado River have led to 

an artificial ecosystem dominated by nonnative species. 

According to Grams et al. (2007, p. 556), models for the 
79

response of the Colorado River downstream from Glen 

Canyon dam should consider “(1) possibility of variable 

responses among different channel elements, and

(2) the potential importance of exceptional flows 

resulting from management decisions,” along with 

the usual factors such as the pre-dam and post-dam 

sediment load, grain size, and average flows.

In analyzing the bed degradation and channel 

adjustment of the Colorado River, Grams et al. 

(2005, 2007, 2010) used many of the techniques 

described in Geological Monitoring chapter on fluvial 

geomorphology (Lord et al. 2009). Glen Canyon 

National Recreation Area resource managers may 

wish to review this chapter in which Lord et al. (2009) 

present an overview of stream dynamics, describe 

factors that may lead to channel instability, and provide 

guidelines on monitoring rivers and streams in the Glen 

Canyon National Recreation Area. Taking an integrated 

system approach, Lord et al. (2009) present vital signs, 

or critical factors, that can be monitored in order to 

establish the overall condition of the river system. These 

vital signs include: (1) watershed landscape (vegetation, 

land use, surficial geology, slopes, and hydrology), 

(2) hydrology (frequency, magnitude, and duration 

of stream flow rates), (3) sediment transport (rates, 

modes, sources, and types of sediment), (4) channel 

cross section, (5) channel planform, and (6) channel 

longitudinal profile (Lord et al. 2009).

Navajo Sandstone and Potential Glen Canyon 

Dam Failure

Participants at the 1999 scoping workshop expressed 

concern that the Glen Canyon Dam could fail because 

it was anchored in the porous Navajo Sandstone (NPS 

Geologic Resources Division and Natural Resources 

Information Division 1999). The two original internal 

spillways were first used during an impressive flood 

in May 1983, three years after Lake Powell had filled. 

Noticeable vibrations and rumblings occurred, and an 

inspection of the spillways found pieces of concrete 

and sandstone in the water. Cavitation had damaged 

and eroded the concrete lining at bends in the spillway 

tunnels. In places, erosion had exposed the relatively 

soft Navajo Sandstone (Jn). 

Following the 1983 flood, the spillways were redesigned 

to reduce or eliminate cavitation and eliminate the 

possibility of the reservoir rising and flowing over the 

crest of the dam. Erosion of the Navajo Sandstone 

around the dam abutments, damage to the power plant 

at the base of the dam, and subsequent failure would 

probably occur if the dam were overtopped by the 

reservoir.

If Glen Canyon Dam were to fail, approximately 33 

km3 (7.9 mi3) of water would surge out of Lake Powell. 

In addition to severely scouring the downstream 

Colorado River channel, damage would occur to every 

downstream community, every downstream dam 

(except possibly Hoover Dam), and every riparian 

ecosystem. Dam failure would also destroy up to 964 

known archaeological sites, including 264 in the Grand 

Canyon (Colorado Riverkeep 2005). Glen Canyon Dam 

is the central part of the Colorado River Storage Project, 

and a dam failure would impact the water supply to 

residences and farmland dependent on Colorado River 

water.

81

Geologic History

This chapter describes the geologic events that formed the present landscape of Glen Canyon National 

Recreation Area.

The rock units in Glen Canyon National Recreation 

Area span approximately 300 million years and 

record the dynamic transition from shallow marine 

environments on the North American continent to 

the carving of the Colorado River through layers of 

bedrock on the Colorado Plateau. As an overview, 

from the Late Pennsylvanian Period to the midTriassic Period, southeastern Utah became part of the 

supercontinent Pangea. Expansive sand deserts (ergs) 

inundated the region in the Jurassic Period, and tracks 

of dinosaurs can be followed to their abrupt end in the 

Late Cretaceous. During the Late Cretaceous–Eocene 

Laramide Orogeny (between about 70 million and 40 

million years ago), the strata on the Colorado Plateau 

were bent into broad folds, such as the Circle Cliffs 

anticline that trends through the recreation area. In the 

late Paleogene Period, approximately 31 million to 23 

million years ago, magma flowed through the crust and 

solidified to form the laccoliths that core the Henry 

and Navajo Mountains. Drainage systems developed 

and approximately 5.5 million years ago, the modern 

Colorado River began carving the Grand Canyon. 

Within about the last 1 million years, the river carved 

the part of Glen Canyon that we see today (it had been 

carving the older, now-missing, Glen Canyon for about 

5.5 million years). Today, these many millions of years 

of Earth history are on display along the shores of Lake 

Powell.

Pennsylvanian and Permian Periods: Shallow 

Seas and Assembling Pangea

Aggressive tectonism in the Pennsylvanian Period 

built mountains in Colorado with as much as 3,000 m 

(10,000 ft) of relief (De Voto 1980). Compression from 

the southwest caused a northwest–southeast trending, 

shallow, subsiding trough called the Paradox Basin to 

form across the Four-Corners area (fig. 42; Stone 1986). 

The Hermosa Group (PNp and PNht) records episodes 

of marine incursions from the south during the 

Pennsylvanian Period. The climate was quite arid in 

Glen Canyon National Recreation Area, and during 

times of sea level fall (regression), seawater evaporated 

and salt deposits formed (Rueger 1996). When relative 

sea level rose during subsequent transgressions, 

normal marine waters returned, salinity fell, and salt 

deposits (anhydrite) were overlain by silty dolomite, 

limestone, and black shale (Hite 1970; Rueger 1996; 

Doelling 2010). The Paradox Formation (PNp) offers 

textbook examples of these cycles of salt, dolomite, 

porous limestones, and black shales. These deposits in 

the Paradox Basin would later become economically 

important when the salt, reacting to overburden 

pressure in the subsurface, flowed upward to form 

anticlines that trapped oil migrating from the black 

shale into porous limestone reservoirs.

By Late Pennsylvanian time, barriers in the Paradox 

Basin that restricted open marine conditions were 

eliminated and unimpeded marine conditions returned 

to the area. The Honaker Trail Formation (PNht) records 

deposition in shallow marine, beach, lagoon, and deltaic 

environments (Rueger 1996; Anderson et al. 2010). The 

interlayered sandstones, mudstones, and fossiliferous 

limestones of the Permian–Pennsylvanian Elephant 

Canyon (PPNe) and Halgaito (PPNhg) formations and 

the lower Cutler beds (PPNcl) were deposited in tidal 

flat, delta, coastal sand dune, fluvial, and shallowmarine shelf environments (Loope 1984; Condon 1997; 

Huntoon et al. 2010).

Approximately 275 million years ago (Early Permian), 

most of Utah was located near 10° north latitude in a 

dry, high pressure climatic belt, analogous to that of 

the Sahara Desert today (fig. 42; Morris et al. 2010). 

An extensive dune field that would become the Cedar 

Mesa Sandstone (Pcm) formed along the sea coast, 

and most of southeastern Utah became covered by an 

extensive coastal dune field. Periodically, sea level rise 

would produce shallow marine incursions, resulting in 

the tidal mud-flat and beach environments preserved in 

parts of the Organ Rock Formation (Po) and White Rim 

Sandstone (Pwr) (Doelling and Davis 1989; Anderson et 

al. 2010).

At the end of the Paleozoic Era, the global landmasses 

sutured together to form the supercontinent Pangea. 

Collisions between these landmasses generated the 

Appalachian mountain chain, the Ouachita Mountains 

of Arkansas and Oklahoma, and the northwest–
82

southeast trending Ancestral Rocky Mountains in 

Colorado.

Much of the Permian strata has been eroded from the 

Glen Canyon region, leaving a gap in the rock record. 

The boundary between the Early Permian Period and 

the Early Triassic Period is marked by the regional TR-1 

unconformity (fig. 4).

Triassic Period: Fluvial Systems in a Tropical 

Climate

In the Early Triassic (251 million to 245 million years 

ago), Pangea was more-or-less centered on the equator 

(fig. 43; Dubiel 1994). To the west, explosive volcanoes 

arose from the sea and formed a north-south trending 

arc of islands along the present-day border of California 

and Nevada (Christiansen et al. 1994; Dubiel 1994; 

Lawton 1994). The western Colorado Plateau region 

consisted of a broad continental shelf that accumulated 

shallow marine to coastal marine sediments while a 

fluvial and floodplain system developed in the eastern 

part of the Colorado Plateau from the erosion of 

Colorado’s Ancestral Rocky Mountains. These deposits 

became the Moenkopi Formation (TRm) (Stewart 

et al. 1972a; Christiansen et al. 1994; Doelling 2010; 

Anderson et al. 2010; Huntoon et al. 2010). Plant and 

animal fossils in the Moenkopi Formation (table 8) 

suggest a shift to a warm tropical climate with likely 

monsoonal, wet-dry conditions (Stewart et al. 1972a; 

Huntoon et al. 2010; Morris et al. 2010).

In the Late Triassic, streams cut valleys into the 

underlying Moenkopi Formation. Paleovalley geometry 

and channel sandstones in Glen Canyon National 

Figure 42. Middle Pennsylvanian (308 million years ago) and Early Permian (280 million years ago) paleogeographic 

maps of North America. As the Paleozoic Era came to a close, subduction zones along the western, southern, and 

eastern margins of present-day North America sutured together North America, South America, and Africa to form 

the supercontinent Pangea. By the Early Permian, the Paradox Basin had closed. The continent-continent collisions 

resulted in the Appalachian Mountain chain as well as the Ancestral Rocky Mountains. The red star approximates the 

location of Glen Canyon National Recreation Area. Yellow arrows represent the direction of plate movement. Base 

paleogeographic maps by Ron Blakey (Colorado Plateau Geosystems, Inc.), available online: http://cpgeosystems.com/

index.html (accessed 12 January 2016). 
83

Figure 43. Mesozoic Era paleogeographic maps of 

North America. In the Triassic Period (245 million 

years ago), Pangea began to split apart, opening 

what would become the Gulf of Mexico and the 

Atlantic Ocean. During the Jurassic (170 million years 

ago), coastal mountains rose along the western coast 

of North America and great deserts of sand (ergs) 

formed as winds from the north funneled sand into 

the region of Glen Canyon National Recreation Area. 

By the Middle Jurassic, a shallow sea encroached into 

the region from the north. By the Late Cretaceous 

(85 million years ago), the Western Interior Seaway 

bisected the North American continent. The red star 

approximates the location of Glen Canyon National 

Recreation Area. Yellow arrows represent the direction 

of plate movement. Dashed yellow line represents 

the approximate boundary between the Farallon and 

Kula plates. Base paleogeographic maps by Ron Blakey 

(Colorado Plateau Geosystems, Inc.), available online: 

http://cpgeosystems.com/index.html (accessed 13 May 

2015).
84

Recreation Area, Capitol Reef National Park, and other 

exposures on the Colorado Plateau provide evidence for 

the development of a dendritic (tree-like) fluvial system 

in southeastern Utah. The main trunk river flowed to 

the northwest, and tributaries drained highlands that 

had risen to the west, southwest, south, and southeast 

(see GRI report by Graham 2006a; Lucas 1993; Dubiel 

1994; Lucas et al. 1997; Morris et al. 2010). The complex 

assemblage of alluvial, marsh, lacustrine, playa, and 

eolian deposits became the Chinle Formation (TRc) 

(Stewart et al. 1972b; Anderson et al. 2010). Interlayered 

with the clastic sediments are beds of bentonite, 

altered volcanic ash that had blown into the area from 

volcanic activity in present-day Arizona and California 

(Christiansen et al. 1994; Anderson et al. 2010). 

Jurassic Period: Extensive Dune Fields

The Jurassic western margin of North America was 

associated with an Andean-type margin where the 

eastward subduction of the seafloor gave rise to 

volcanism similar to that found in the modern Andes 

of South America. Volcanoes formed an arcuate north–

south chain of mountains off the coast in what is now 

central Nevada. The northwest–southeast-trending 

Uncompahgre Uplift, that part of the Ancestral Rocky 

Mountains in western Colorado, and the Monument 

Upwarp in eastern Utah, east of present-day Glen 

Canyon National Recreation Area, remained slightly 

topographically high during the Jurassic. 

The Four-Corners area of Arizona, New Mexico, 

Colorado, and Utah during the Early Jurassic was 

covered by extensive ergs, similar to the modern Sahara/

Sahel regions (fig. 43). Southeastern Utah was located 

about 18° north latitude at the beginning of the Jurassic 

(about 199 million years ago) and moved to 30°–35° 

north latitude by the end of the Jurassic (about 145 

million years ago) (Kocurek and Dott 1983; Peterson 

1994). This is the latitude of the present day northeast 

trade wind belt where cool, dry air descends from the 

upper atmosphere and sweeps back to the equator in a 

northeast–southwest direction. The cool, dry air warms 

and expands and sucks up any additional moisture from 

the land’s surface. 

The Jurassic deserts that inundated the Colorado 

Plateau for roughly 40 million years (not counting the 

time represented by erosion) contained sand dunes 

that may be the largest recorded in the history of 

Earth (Kocurek and Dott 1983). Like the Sahara, these 

were ergs that formed on a coastal and inland dune 

field, and they affected the present areas of southern 

Montana, western Wyoming, eastern Idaho, eastern 

Utah, westernmost Colorado, southwest Colorado, 

northeastern Arizona, and northwestern New Mexico 

(Kocurek and Dott 1983; Peterson 1994). 

During the Latest Triassic to Early Jurassic, wind 

transported abundant quantities of sand eroded from 

Paleozoic sandstones exposed from as far north as 

Montana and Alberta to the Colorado Plateau (Kocurek 

and Dott 1983). These dunes became the Wingate 

Sandstone (JTRw). Sinuous rivers meandered in a 

general westward to southwestward direction across 

a broad floodplain in southeastern Utah, depositing 

fluvial and floodplain sediments that formed the 

Kayenta Formation (Jk) (Anderson et al. 2010; Morris et 

al. 2010).

Extensive ergs returned to the Colorado Plateau as 

the region became increasingly arid. Lower Jurassic 

Navajo Sandstone (Jn) dune deposits are as much as 

340 m (1,100 ft) thick below the dam in Glen Canyon. 

The sand dunes gradually overtook the fluvial systems 

of the Kayenta Formation. In contrast to the Wingate 

Sandstone, most of the sand that formed the Navajo 

dunes originated from the ancestral Appalachian 

Mountains (Dickinson and Gehrels 2003, 2009; Rahl 

et al. 2003; Biek et al. 2010). A continental-scale river 

system transported the sand grains to the western shore 

of the Jurassic margin of North America. Winds from 

the north and northwest blew the sand southward to be 

incorporated into the vast dune field represented by the 

regional Navajo, Nugget, and Aztec sandstones. Broad 

shallow lakes formed in interdunal desert oases that 

were scattered throughout the coastal Navajo dune field 

(Anderson et al. 2010). 

Early Jurassic compressional deformation along the 

western margin of North America preserved this 

tremendous thickness of eolian sand (Allen et al. 2000). 

As North America collided with the oceanic plate, the 

continental interior flexed downward, providing space 

for sediment to accumulate. Along the continental 

margin, west of the Glen Canyon region, mountains 

rose and blocked any moisture blowing in from the 

western ocean, increasing aridity.

The regional J-1 unconformity separates the Navajo 

Sandstone from the eolian and fluvial sandstones of 

the Middle Jurassic Temple Cap Formation, which is 
85

mapped as the Page Sandstone (Jp) in the GRI GIS data 

(fig. 4; see posters [in pocket]). Interbedded sandstones 

and siltstones, fossil-bearing limestone, and gypsum 

record episodes of intermittent marine flooding and 

evaporation in the Glen Canyon area (Anderson et al. 

2010; Morris et al. 2010). A broad depression called the 

Utah-Idaho trough was inundated by a sea encroaching 

onto the continent from the north. Associated with the 

advancing sea were shallow marine, marginal marine, 

and sabkha environments.

The members of the overlying Carmel Formation (Jc) 

represent two transgressive-regressive cycles. In Glen 

Canyon National Recreation Area, the first cycle is 

represented by the transgressive Judd Hollow Member 

(Jcj) and the regressive Thousand Pockets Member (Jpt) 

(Doelling et al. 2013). The transgressive Paria River 

Member (Jcp) marks the rise in sea level that initiated 

the second cycle, and the Winsor Member (Jcw) was 

deposited as the shoreline regressed to the northwest. 

During regressions, northward-flowing streams carried 

sand eroded from highlands covered with Navajo 

Sandstone, and wind reworked the sand into coastal 

dunes. These fluvial-eolian deposits were inundated 

by the sea during transgressive episodes (Blakey 1994; 

Anderson et al. 2010; Doelling et al. 2013). 

The Entrada dunes formed following the final 

regression of the Carmel sea from the region. The 

Entrada Sandstone (Je) dune fields became the most 

widespread of the preserved late Paleozoic and 

Mesozoic wind-blown deposits on the Colorado 

Plateau (Peterson 1994). 

Mudcracks, ripple marks, and inch-scale crossbedding in the overlying Summerville Formation (Jesu) 

represent tidal flat deposition. These marginal marine 

conditions resulted from a major transgression of the 

inland seaway from the north at the end of the Middle 

Jurassic and beginning of the Late Jurassic (about 157 

million years ago). Deposits from fluctuating sea levels 

mark the end of the vast ergs that once covered the 

Colorado Plateau (Kocurek and Dott 1983). Shallow 

marine, tidal flat, and eolian deposits of the Romana 

Sandstone (Jr) spread over the region. In the Late 

Jurassic, sea level fell, and the extensive Morrison 

Formation (Jm) was deposited in river floodplains 

across western North America (Lawton 1994; Anderson 

et al. 2010).

Cretaceous Period: Western Interior Seaway

No Early Cretaceous deposits are known from 

southeastern Utah, probably because the area was 

undergoing erosion rather than deposition. From 

approximately 155 million years to 50 million years 

ago, the western margin of North America became 

a subduction zone and tectonic forces compressed, 

folded, and faulted rocks from Alaska to northern 

Mexico and thrust them eastward as if a giant accordion 

was being squeezed. Older Paleozoic rocks were thrust 

over younger strata, thickening the crust until the 

sedimentary layers at the bottom of these kilometerscale thrust stacks were metamorphosed (Oldow et 

al. 1989; Lageson and Schmitt 1994; Lawton 1994; 

DeCelles 2004). 

The Sevier Orogeny, a mountain-building event that 

occurred between 140 million and 50 million years 

ago, generated a rugged north–south trending foldand-thrust belt in central Utah. Rivers flowing from 

the early Sevier highlands deposited the sediments 

found in the lower Dakota Sandstone (Kd). As thrust 

sheets stacked atop one another, the crust parallel to the 

Sevier mountain range began to subside, and marine 

incursions produced the lagoons, beaches, and swamps 

documented in the upper Dakota Sandstone. 

With subsidence, sea water began to fill the basin from 

the Arctic region and the Gulf of Mexico. Episodic 

fluctuations in sea level occurred throughout the 

Cretaceous, culminating in the formation of the most 

extensive interior seaway ever to bisect the North 

American continent (fig. 43). The Western Interior 

Seaway extended from today’s Gulf of Mexico to the 

Arctic Ocean, a distance of about 4,800 km (3,000 

mi; Kauffman 1977; Steidtmann 1993). At maximum 

sea level rise, the width of the basin reached 1,600 

km (1,000 mi). The Mancos Shale (Km) and Tropic 

Shale (Kt) in Glen Canyon National Recreation Area 

accumulated in this seaway (Elder and Kirkland 1994; 

Anderson et al. 2010). When sea level fell, the shoreface, 

beach, lagoon, and paludal environments of the Straight 

Cliffs Formation (Ks) were deposited (Anderson et al. 

2010). Peat beds in the swamps and lagoons were buried 

and eventually transformed into thick coal deposits.

Cretaceous–Paleogene Periods: The Laramide 

Orogeny

The Western Interior Seaway receded from the 

continental interior with the onset of the Laramide 
86

Orogeny. The Laramide Orogeny occurred from about 

70 million years ago (latest Cretaceous Period) to 40 

million years ago (Eocene Epoch of the Paleogene 

Period) and overlaps the Sevier Orogeny by about 25 

million years (Hintze and Kowallis 2009; Biek et al. 

2009; Grant Willis, Utah Geological Survey, geologist, 

written communication, 1 December 2015). The Drip 

Tank Member (Ksd) of the Straight Cliffs Formation 

and the Dakota Formation (Kd) form the crest of the 

Smoky Mountain anticline in the southern part of the 

recreation area. Deformation of these strata indicates 

that the initiation of the Laramide Orogeny in this 

region had to have occurred after deposition of these 

Late Cretaceous units. 

The Laramide Orogeny resulted from a profound 

eastward shift in tectonic activity along the western 

margin of North America. The angle of the subducting 

plate flattened and compressive forces were felt far 

inland. Rather than generating volcanic mountain 

ranges on the west coast as in previous orogenies, 

the Laramide Orogeny displaced deeply buried 

Precambrian plutonic and metamorphic rocks along 

reverse faults and folded the strata on the Colorado 

Plateau into asymmetric, north- to northwesttrending anticlines and synclines, such as the Circle 

Cliffs anticline, the associated Waterpocket Fold, 

and the secondary folds of the Kaiparowits basin 

(fig. 23). During folding of the Echo Cliffs monocline 

southeast of the southern end of the recreation area, 

the Navajo Sandstone was intensely brecciated (TKb). 

The broad, asymmetrical, north–south-trending 

Monument monocline formed in southeastern Utah 

and northeastern Arizona at this time. Its gently dipping 

western flank exposes Pennsylvanian and Permian 

rocks in the eastern part of the recreation area.

The regional increase in heat flow from the Laramide 

Orogeny also affected oil migration. The thermal history 

of the White Rim Sandstone (Pwr) in the Hite area 

constrains oil migration into the Tar Sand Triangle to 

sometime between the latest Cretaceous to the earliest 

Paleogene (Oligocene Epoch) (Huntoon et al. 1999). 

Paleogene Period (Oligocene Epoch): 

Laccolith Emplacement

From about 31.2 million to 23.3 million years ago 

(Oligocene Epoch), laccoliths domed up the five steepsided mountains in the Henry Mountains (Anderson 

et al. 2010). These igneous intrusions injected along 

bedding planes in Cretaceous and Permian sedimentary 

rocks that are now exposed on the Colorado Plateau, 

and probably in older still buried rocks as well.

The laccolith that formed the broad dome of Navajo 

Mountain is not exposed, so its age has not been 

determined as accurately as the laccoliths in the Henry 

Mountains. The intrusion deformed Jurassic and 

Triassic strata and is capped by the Cretaceous Dakota 

Sandstone (Anderson et al. 2010). Field relations suggest 

that the Navajo Mountain laccolith may be correlative 

with the Henry Mountains laccoliths, or it may be 

related to the 71 million to 74 million year old laccoliths 

that core the Carrizo Mountains in northeastern 

Arizona (Semken and McIntosh 1997; Anderson et al. 

2010).

Paleogene–Quaternary Periods: Colorado 

River System and Carving Glen Canyon

The Colorado Plateau uplifted and the landscape 

transformed from one of deposition to one of erosion 

beginning in the Paleogene Period, which began about 

66 million years ago (Anderson et al. 2010). Running 

water, wind, and mass wasting removed several 

thousand meters of sedimentary rock. Rivers flowed 

north to northeast, draining into lake basins in central 

and northeastern Utah (Blakey and Ranney 2008; 

Anderson et al. 2010). Erosion has removed most of the 

evidence of this drainage pattern.

About 5.5 million years ago, these northern drainages 

were captured by lower drainages in the Lake Mead 

area that flowed to the Gulf of California. The 

integration of these drainages resulted in the modern 

southwest-flowing Colorado River and led to the 

dramatic carving of Glen Canyon and the Grand 

Canyon in only a few million years (Karlstrom et al. 

2008; Anderson et al. 2010). As the Colorado Plateau 

continued to rise, the Colorado River incised rapidly 

into relatively soft Cretaceous, Jurassic, and Triassic 

strata. Narrow slot canyons were carved into more 

resistant strata and wide valleys formed in softer strata 

(Anderson et al. 2010; Huntoon et al. 2010). Vertical 

incision entrenched the meanders of tributary channels 

as they attempted to keep pace with the downcutting of 

the Colorado River. 

Erosion may have accelerated during the wet 

Pleistocene Epoch (2.6 million to 11,700 years ago). 

Glacial ice scoured the top of Boulder Mountain and 

the Aquarius Plateau, west of Capitol Reef National 
87

Park, and a broad tongue of ice extended into the 

lowlands near Grover, southwest of Fruita, the bestknown settlement in Capitol Reef National Park (see 

GRI report by Graham 2006a; Smith et al. 1963; Morris 

et al. 2010). Although erosion may have accelerated 

during the Pleistocene, incision of the Colorado River 

probably did not. Incision is controlled by the base level 

of the river, which is controlled by tectonic activity.

Meltwater from the glaciers flowed down valleys and 

spread outwash gravels along the drainage routes. Steep, 

rain-saturated slopes collapsed, resulting in some of 

the landslide and other mass movement deposits (Qm) 

in the recreation area. Some of the unconsolidated 

alluvial gravel deposits (Qa) in Glen Canyon National 

Recreation Area may have originated as glacial 

outwash. Today, the gravels cap terraces that were once 

floodplains before the Colorado River and its tributaries 

incised farther into the underlying bedrock.

Glen Canyon National Recreation Area And 

Other NPS Areas Along The Colorado River

Until 1963 when Glen Canyon Dam closed, the 

Colorado River flowed freely through Glen Canyon, 

continuing its natural incision of bedrock and 

depositing fresh sediments in the canyons. Today, silt 

accumulates at the sites of inflow deltas, such as the 

Hite delta, and the natural processes that produced 

the dynamic landscape of Glen Canyon National 

Recreation Area have been altered and subdued. 

Visitors with boats can easily access many geologic 

wonders.

Glen Canyon National Recreation Area is one in a 

series of National Park Service units that preserve and 

protect the exceptional landscape and expansive vistas 

of the Colorado Plateau along its namesake river. To 

the north, Canyonlands National Park protects the 

canyons, mesas, buttes, and spires that formed adjacent 

to the confluence of the Colorado and Green rivers 

(plate 1; National Park Service 2013). The expansive 

vistas include the La Sal, Abajo, Henry, and Navajo 

mountains. The Canyonlands landscape formed 

over hundreds of millions of years and preserves 

geologic processes such as sedimentation, erosion, salt 

dissolution and tectonics, and meteorite impact. As with 

the other parks along the Colorado River, Canyonlands 

preserves extensive fossil evidence of prehistoric life. 

Primarily a backcountry park, Canyonlands National 

Park offers visitors the opportunity to experience 

remote wilderness and solitude. 

South of Glen Canyon National Recreation Area, 

the Colorado River flows through Grand Canyon 

National Park, established to preserve and protect the 

canyon’s world renown vistas and unique geologic, 

paleontologic, and natural and cultural features 

(National Park Service 2010). One of the planet’s most 

iconic geologic landscapes, Grand Canyon was carved 

by the Colorado River over the last six million years by 

the same erosional and tectonic processes that continue 

to shape the canyon today. The exposed layers of rock 

in the Grand Canyon provide scientific evidence of 

depositional environments and tectonic processes that 

spans more than one third of Earth’s history. Geologic 

features, geologic processes, paleontological resources, 

and cave resources are included among the park’s 

fundamental resources and values (National Park 

Service 2010).

Lake Mead National Recreation Area shares a border 

with Grand Canyon National Park. Like Lake Powell, 

Lake Mead offers recreational opportunities, but the 

area also includes fundamental geologic resources 

such as deep canyons, dry washes, sheer cliffs, vistas of 

mountain ranges, and a variety of rock formations. The 

rugged desert landscape contrasts vividly with the vast 

water bodies. The landscape reflects the diverse array 

of geologic, geomorphic, and hydrogeologic features 

and processes. As in the other parks, fossil resources, 

wilderness, and desert ecosystems are considered 

valuable fundamental resources in Lake Mead National 

Recreation Area (National Park Service 2015h).

89

Geologic Map Data

This chapter summarizes the geologic map data available for Glen Canyon National Recreation Area. 

Posters (in pocket) display the map GIS data draped over imagery of the park and surrounding area. 

The Map Unit Properties Tables (in pocket) summarizes this report’s content for each geologic map 

unit. Complete GIS data are included on the accompanying CD and are also available at the GRI 

publications website: http://go.nps.gov/gripubs.

Geologic Maps

Geologic maps facilitate an understanding of an area’s 

geologic framework and the evolution of its present 

landscape. Using designated colors and symbols, these 

maps portray the spatial distribution and temporal 

relationships of rocks and unconsolidated deposits. The 

American Geosciences Institute website, http://www.

americangeosciences.org/environment/publications/

mapping, provides more information about geologic 

maps and their uses.

Source Maps

The GRI team digitizes paper maps and converts digital 

data to conform to the GRI GIS data model. The GRI 

digital geologic map product includes essential elements 

of the source maps such as map unit descriptions, a 

correlation chart of units, a map legend, map notes, 

cross-sections, figures, and references. The GRI team 

used a compiled map (Willis and Ehler in prep.) as the 

primary source map. That compiled map incorporated 

geologic information from many published maps listed 

below. These sources also provided information for this 

report. 

Billingsley, G. H., P. W. Huntoon, and W. J. Breed. 1987. 

Geologic map of Capitol Reef National Park and vicinity, 

Emery, Garfield, Kane, and Wayne Counties, Utah (scale 

1:62,500). Map 87. Utah Geological and Mineral Survey, 

Salt Lake City, Utah.

Doelling, H. H. 2004. Geologic map of the La Sal 30’x60’ 

quadrangle, San Juan County, Utah (scale 1:100,000). Map 

205. Utah Geological Survey, Salt Lake City, Utah.

Doelling, H. H., and F. D. Davis. 1989. The geology of Kane 

County, Utah, geology, mineral resources, geologic hazards 

(scale 1:100,000). Bulletin 124 (also published separately as 

Map 121). Utah Geological and Mineral Survey, Salt Lake 

City, Utah.

Doelling, H. H., and G. C. Willis. 1999. Interim geologic map 

of the Escalante and parts of the Loa and Hite Crossing 

30’x60’ quadrangles, Garfield and Kane Counties, Utah 

(scale 1:100,000). Open-File Report 368. Utah Geological 

Survey, Salt Lake City, Utah.

Doelling, H. H., and G. C. Willis. 2006. Geologic map of the 

Smoky Mountain 30’x60’ quadrangle, Kane and San Juan 

Counties, Utah, and Coconino County, Arizona (scale 

1:100,000). Map 213, 2 plates. Utah Geological Survey, Salt 

Lake City, Utah. 

Doelling, H. H., and G. C. Willis. 2007. Geologic map of 

the lower Escalante River area, Glen Canyon National 

Recreation Area, eastern Kane County, Utah (scale 

1:100,000). Miscellaneous Publications 06-3DM (GIS data). 

Utah Geological Survey, Salt Lake City, Utah.

Huntoon, P. W., G. H. Billingsley, Jr., and W. J. Breed. 1982. 

Geologic map of Canyonlands National Park and vicinity, 

Utah (scale 1:62,500). Canyonlands Natural History 

Association, Moab, Utah.

Phoenix, D. A. 2009. Geologic map of part of the Lees 

Ferry area, Coconino County, Arizona (scale 1:24,000). 

Miscellaneous Publication 09-2DM (digitized and modified 

from plate 1 of US Geological Survey Bulletin 1137, scale 

1;24,000, published in 1963). Utah Geological Survey, Salt 

Lake City, Utah.

Thaden, R. E., A. F. Trites, Jr., T. L. Finnell, and G. C. Willis. 

2008. Geologic map of the White Canyon-Good Hope 

Bay area, San Juan and Garfield Counties, Utah (scale 

1:100,000). Miscellaneous Publication 08-3DM (digitized 

and modified from plate 1 of US Geological Survey Bulletin 

1125, scale 1:24,000, published in 1964). Utah Geological 

Survey, Salt Lake City, Utah.

Willis, G. C. 2004. Interim geologic map of the lower San Juan 

River area, eastern Glen Canyon National Recreation Area 

and vicinity, San Juan County, Utah (scale 1:50,000). OpenFile Report 443DM (GIS data). Utah Geological Survey, Salt 

Lake City, Utah.

Willis, G. C. 2009a. Geologic map of the Hite Crossing–lower 

Dirty Devil River area, Glen Canyon National Recreation 

Area, Garfield and San Juan Counties, Utah (scale 

1:100,000). GIS data. Utah Geological Survey, Salt Lake 

City, Utah.

Willis, G. C. 2009b. Interim geologic maps of the Bullfrog, 

Halls Crossing, Halls Crossing NE, Ticaboo Mesa, and 

Knowles Canyon quadrangles, Glen Canyon National 

Recreation Area, Garfield and San Juan Counties, Utah 

(scale 1:24,000). Open-File Report. Utah Geological Survey, 

Salt Lake City, Utah.
90

Willis, G. C. 2009c. Geologic map of the Glen Canyon Dam 

area, Glen Canyon National Recreation Area, Arizona and 

Utah (scale 1:24,000). GIS data. Utah Geological Survey, 

Salt Lake City, Utah.

GRI GIS Data

The GRI team implements a GIS data model that 

standardizes map deliverables. The data model is 

available at http://go.nps.gov/gridatamodel. This data 

model dictates GIS data structure, including layer 

architecture, feature attribution, and relationships 

within ESRI ArcGIS software. The GRI team digitized 

the data for the park using data model version 2.1. 

The GRI Geologic Maps website, http://go.nps.gov/

geomaps, provides more information about GRI map 

products. 

GRI GIS data are publically available through the NPS 

Integrated Resource Management Applications (IRMA) 

portal (https://irma.nps.gov/App/Portal/Home). Enter 

“GRI” as the search text and select a park from the unit 

list.

The following components are part of the GRI GIS 

data:

● a GIS readme file (glca_gis_readme.pdf) 

that describes the GRI data formats, naming 

conventions, extraction instructions, use 

constraints, and contact information;

● data in ESRI geodatabase GIS format;

● layer files with feature symbology (table 11);

● Federal Geographic Data Committee (FGDC)–

compliant metadata;

● an ancillary map information document (glca_

geology.pdf) that contains information captured 

from source maps such as map unit descriptions, 

geologic unit correlation tables, legends, crosssections, and figures; and

● an ESRI map document (glca_geology.mxd) that 

displays the GRI GIS data.

● a version of the data viewable in Google Earth 

(glca_geology.kmz) (table 11).

GRI Posters

 Three posters of the GRI GIS data, draped over a 

shaded relief image of the park and surrounding area, 

are included with this report (in pocket). Not all GIS 

feature classes are included on the poster (table 11). 

Geographic information and selected park features have 

been added to the poster. Digital elevation data and 

added geographic information are not included in the 

GRI GIS data set, but are available online from a variety 

of sources. Contact GRI for assistance locating these 

data.

Map Unit Properties Tables

The Bedrock and Unconsolidated Map Unit Properties 

Tables (in pocket) list the geologic time division, 

symbol, and a simplified description for each of the 

geologic map units in the GRI GIS data. Following 

the structure of the report, the tables summarize the 

geologic features, processes, resource management 

issues, and history associated with each map unit. 

Use Constraints

Graphic and written information provided in this 

report is not a substitute for site-specific investigations. 

Ground-disturbing activities should neither be 

permitted nor denied based upon the information 

provided here. Please contact GRI with any questions.

Minor inaccuracies may exist regarding the locations 

of geologic features relative to other geologic or 

geographic features on the poster. Based on the source 

map scale (1:24,000 to 1:100,000) and US National Map 

Accuracy Standards, geologic features represented in 

the geologic map (GRI GIS) data are expected to be 

horizontally within 12 m (40 ft) to 51 m (167 ft) of their 

true locations.
91

Table 11. Geology data layers in the Glen Canyon National Recreation Area GRI GIS data.

Data Layer On GRI Posters? Google Earth Layer?

Geologic Attitude Observation Localities (strike, dip, trend data) No No

Mine Point Features (NPS access only) No No

Geologic Point Features (natural arches and springs) Yes No

Structure Contours Showing Base of the Navajo Sandstone No No

Structure Contours Showing Base of the Carmel Formation No No

Structure Contours Showing Top of the Navajo Sandstone No No

Structure Contours Showing Top of the Permian No No

Structure Contours Showing Top of the Morrison Formation No No

Structure Contours Showing Top of the Wingate Sandstone No No

Structure Contours Showing Top of the Permian and the Hoskinnini Member of the 

Moenkopi Formation No No

Structure Contours Showing Top of the White Rim Sandstone No No

Geologic Line Features (mineralized veins) No No

Map Symbology Yes No

Linear Joints Yes Yes

Folds Yes Yes

Faults Yes Yes

Major Water Body Extent (approximate extent of Lake Powell) Yes No

Geologic Contacts No Yes

Geologic Units Yes Yes
92

Glossary

These are brief definitions of selected geologic terms relevant to this report. Definitions are based on 

those in the American Geosciences Institute Glossary of Geology (5th edition; 2005). Additional terms 

are defined at http://geomaps.wr.usgs.gov/parks/misc/glossarya.html.

abandoned mineral lands (AML). Lands, waters, and 

surrounding watersheds that contain facilities, structures, 

improvements, and disturbances associated with 

past mineral exploration, extraction, processing, and 

transportation.

abandoned mineral lands (AML) feature. An individual 

element of an AML site, such as vertical shaft, adit, open 

stope, open pit, highwall, prospect, or associated structures. 

abandoned mineral lands (AML) site. An area composed of 

AML features associated with past mineral exploration, 

extraction, processing, and transportation operations.

absolute age. The geologic age (in years) of a fossil, rock, 

feature, or event. The term is now in disfavor as it implies a 

certainty or exactness that may not be possible by present 

dating methods. See “isotopic age” and “radiometric age.”

accretion (sedimentary). The gradual addition of new land 

to an existing landmass by the deposition of sediment, for 

example, on a beach by the washing up of sand from the 

sea.

active margin. A tectonically active plate boundary where 

lithospheric plates are converging, diverging, or sliding past 

one another. 

adit. A horizontal passage into a mine from the surface.

eolian. Describes materials formed, eroded, or deposited by 

or related to the action of wind. 

aggradation. The building up of Earth’s surface by 

depositional processes.

allochem. A collective term for one of several varieties of 

discrete and organized carbonate aggregates that serves 

as the coarser framework grains in most mechanically 

deposited limestones, as distinguished from sparry calcite 

(usually cement) and carbonate-mud matrix (micrite).

alluvial fan. A low, relatively flat to gently sloping, fanshaped mass of loose rock material deposited by a stream, 

especially in a semiarid region, where a stream issues from a 

canyon onto a plain or broad valley floor.

alluvial terrace. A stream terrace composed of 

unconsolidated alluvium produced by a rejuvenated stream 

via renewed downcutting of the floodplain or valley floor, 

or by the covering of a terrace with alluvium.

alluvium. Stream-deposited sediment.

anhydrite. A sulfate (sulfur + oxygen) mineral composed of 

anhydrous calcium sulfate, CaSO4; readily alters to gypsum 

(hydrous calcium sulfate).

anticline. A fold, generally convex upward (“A”-shaped) 

whose core contains the stratigraphically older rocks. 

aquifer. A rock or sedimentary unit that is sufficiently porous 

to hold water, sufficiently permeable to allow water to move 

through it, and saturated to some level.

aragonite. A carbonate (carbon + oxygen) mineral of calcium, 

CaCO3; the second most abundant cave mineral after 

calcite, differing from calcite in its crystal structure.

argillaceous. Pertaining to, largely composed of, or containing 

clay-size particles or clay minerals.

arroyo. A small, deep, flat-floored channel or gully of an 

ephemeral stream in the arid and semiarid regions of the 

southwestern United States.

ash. Fine-grained material, less than 2 mm (0.08 in) across, 

ejected from a volcano.

axis. A straight-line approximation of the trend of a fold 

along the boundary between its two limbs. “Hinge line” is a 

preferred term.

badlands. Eroded topography characterized by steep slopes 

and surfaces with little or no vegetative cover; composed of 

unconsolidated or poorly cemented clays or silts.

base flow. Streamflow supported by groundwater and not 

attributed to direct runoff from precipitation or snow melt.

base level. The lowest level to which a stream channel can 

erode. The ultimate base level is sea level, but temporary, 

local base levels exist. 

basement. The undifferentiated rocks, commonly igneous and 

metamorphic, that underlie rocks exposed at the surface, 

commonly sedimentary. In many regions the basement is of 

Precambrian age, but it may be much younger. Also, Earth’s 

crust below sedimentary deposits that extends down to the 

Mohorovicic discontinuity.

basin (structural). A doubly plunging syncline in which rocks 

dip inward from all sides.

basin (sedimentary). Any depression, from continental to 

local scale, into which sediments are deposited.

bathymetry. The measurement of ocean or lake depths and 

the charting of the topography of the ocean or lake floor. 
93

beach. The unconsolidated material at the shoreline that 

covers a gently sloping zone, typically with a concave 

profile, extending landward from the low-water line to 

the place where there is a definite change in material or 

physiographic form (e.g., a cliff), or to the line of permanent 

vegetation (usually the effective limit of the highest storm 

waves).

beach face. The section of the beach normally exposed to the 

action of wave uprush.

bed. The smallest sedimentary stratigraphic unit, commonly 

ranging in thickness from about 1 cm (0.4 in) to 1 to 2 m (40 

to 80 in) and distinguishable from beds above and below.

bedding. Depositional layering or stratification of sediments.

bedrock. Solid rock that underlies unconsolidated 

sedimentary deposits and soil.

benthic. Pertaining to the ocean bottom or organisms living 

on or in substrate; also, referring to that environment.

bentonite. Soft clay or greasy claystone composed mostly of 

the clay mineral smectite, formed by the chemical alteration 

of glassy volcanic ash in contact with water.

bioherm. A moundlike, domelike, lenslike, or reeflike mass 

of rock built up by sedentary organisms, composed almost 

exclusively of their calcareous remains, and enclosed or 

surrounded by rock of different lithology.

bioturbation. The reworking of sediments by organisms.

body fossil. Evidence of past organisms such as bones, teeth, 

shells, or leaf imprints. 

boundstone. A term used for a sedimentary carbonate rock 

whose original components were bound together during 

deposition and remained substantially in the position of 

growth (as shown by such features as intergrown skeletal 

matter and lamination contrary to gravity).

brachiopod. Any marine invertebrate belonging to the phylum 

Brachiopoda, characterized by two bilaterally symmetrical 

valves that are commonly attached to a substratum but may 

also be free. Range: Lower Cambrian to Holocene.

braided stream. A sediment-clogged stream that forms 

multiple channels that divide and rejoin.

breccia. A coarse-grained, generally unsorted sedimentary 

rock consisting of cemented angular clasts more than 2 mm 

(0.08 in) across. 

brecciation. Formation of a breccia, as by crushing or breaking 

a rock into angular fragments.

bryozoan. Any invertebrate belonging to the phylum Bryozoa; 

characterized by colonial growth and a calcareous skeleton. 

Range: Ordovician (and possibly Upper Cambrian) to 

Holocene.

burrow. A tubular or cylindrical hole or opening, made in 

originally soft or loose sediment by a mud-eating worm, 

mollusk, or other invertebrate; may be later filled with clay 

or sand and preserved.

calcareous. Describes a substance that contains calcium 

carbonate. When applied to a rock name it implies that as 

much as 50% of the rock is calcium carbonate.

calcium carbonate. CaCO3. A solid occurring in nature as 

primarily calcite and aragonite. 

calcic. Describes a mineral or igneous rock containing a 

significant amount of calcium.

calcite. A carbonate (carbon + oxygen) mineral of calcium, 

CaCO3; calcium carbonate. It is the most abundant cave 

mineral.

calcrete. A deposit of calcium carbonate that forms a 

cemented layers within a soil profile. Synonymous with 

“caliche,” especially used in the southwestern United States. 

caliche. A hard layer of cemented calcium carbonate, 

commonly on or near the surface in arid and semiarid 

regions.

carbonaceous. Describes a rock or sediment with 

considerable carbon, especially organic material, 

hydrocarbon, or coal.

carbonate. A mineral group composed of carbon and oxygen 

plus an element or elements; for example calcite, CaCO3

; 

and dolomite, CaMg(CO3)2.

carbonate rock. A rock, for example, limestone, calcite, and 

dolomite, that consist primarily of carbonate minerals.

cement (sedimentary). Mineral material, usually chemically 

precipitated, that occurs in the spaces among the individual 

grains of a sedimentary rock, thus binding the grains 

together.

cementation. The process by which clastic sediments become 

lithified or consolidated into hard, compact rocks, usually 

through deposition or precipitation of minerals in the 

spaces among the individual grains of the sediment; may 

occur simultaneously with sedimentation or at a later time.

cephalopod. A marine mollusk of the class Cephalopoda, 

characterized by a head surrounded by tentacles and, in 

most fossil forms, a straight, curved, or coiled calcareous 

shell divided into chambers. Range: Cambrian to Holocene. 

chalcedony. A cryptocrystalline variety of quartz.

channel. The bed of a stream or river. Also, a natural 

passageway or depression of perceptible extent containing 

continuously or periodically flowing water, or forming a 

connecting link between two bodies of water.
94

chemical weathering. Chemical breakdown of minerals at 

Earth’s surface via reaction with water, air, or dissolved 

substances; commonly results in a change in chemical 

composition providing more stability in the current 

environment.

chert. An extremely hard sedimentary rock with conchoidal 

fracturing, consisting mostly of interlocking crystals of 

quartz. 

chronology. The arrangement of events in their proper 

sequence in time.

clast. An individual constituent, grain, or fragment of a rock 

or unconsolidated deposit, produced by the mechanical or 

chemical disintegration of a larger rock mass.

clastic. Describes rocks or sediments made of fragments of 

preexisting rocks.

clay. Minerals and sedimentary fragments that are less than 

1/256 mm (0.00015 in) across.

clay mineral. Any mineral occurring in the clay-sized fraction 

with the understanding that size imposes physical and 

chemical characteristics. 

claystone (sedimentary). An indurated rock with more than 

67% clay-sized minerals.

coal. An organic sedimentary rock consisting of carbon, 

hydrogen, and oxygen, with some sulfur and nitrogen. 

Formed by the destructive distillation of plant remains 

under anaerobic and progressively rising pressures and 

temperatures.

coarse-grained. Describes a crystalline rock and texture 

in which the individual minerals are relatively large, 

specifically an igneous rock whose particles have an 

average diameter greater than 5 mm (0.2 in). Also, describes 

sediment or sedimentary rock and texture in which the 

individual constituents are easily seen with the unaided 

eye, specifically sediment or rock whose particles have an 

average diameter greater than 2 mm (0.08 in).

coastal plain. Any lowland area bordering a sea or ocean, 

extending inland to the nearest elevated land, and sloping 

very gently seaward; may result from the accumulation of 

material along a coast.

colluvium. A loose, heterogeneous, and incoherent mass 

of rock fragments and soil material deposited via surface 

runoff or slow continuous downslope creep; usually 

collects at the base of a slope or hillside, but includes loose 

material covering hillsides.

compaction. The process whereby fine-grained sediment is 

converted to consolidated rock.

compression. A decrease in volume of material (including 

Earth’s crust) as it is pressed or squeezed together.

concordant. Describes a stratum with contacts parallel to the 

orientation of adjacent strata.

concretion. A hard, compact aggregate of mineral matter, 

rounded to irregularly shaped; composition generally differs 

from that of the rock in which it occurs.

conglomerate. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented, rounded clasts 

larger than 2 mm (0.08 in) in diameter.

conodont. One of a number of small fossil elements assigned 

to the order Conodontophorida; commonly toothlike in 

form but not necessarily in function.

contact. The surface between two types or ages of rocks.

continental. Formed on land rather than in the sea. 

Continental deposits may be of lake, swamp, wind, stream, 

or volcanic origin.

coprolite. Fossilized feces.

coral. Any of a large group of bottom-dwelling, sessile, marine 

invertebrate organisms (polyps) that belong to the class 

Anthozoa (phylum Cnidaria), characterized by production 

of an external skeletons of calcium carbonate; may exist as 

solitary individuals or grow in colonies. Range: Abundant in 

the fossil record in all periods later than the Cambrian.

craton. The relatively old and geologically stable interior of a 

continent. 

crinoid. A marine invertebrate (echinoderm) that uses a stalk 

to attach itself to a substrate; “arms” are used to capture 

food. Range: Paleozoic to Holocene, through very common 

in the Paleozoic and rare today.

cross-bed. A single bed, inclined at an angle to the main planes 

of stratification; the term is commonly restricted to a bed 

that is more than 1 cm (0.4 in) thick.

cross-bedding. Uniform to highly varied sets of inclined beds 

deposited by wind or water that indicate flow conditions 

such as direction and depth. 

cross section. A graphic interpretation of geology, structure, 

or stratigraphy based on mapped and measured geologic 

extents and attitudes, depicted in a vertical plane (i.e., a cut 

or profile view).

cross-stratification. Arrangement of strata inclined at an 

angle to the main stratification. This is a general term that 

is commonly divided into cross-bed, which is cross-strata 

thicker than 1 cm (0.4 in); and cross-lamination, which is 

cross-strata thinner than 1 cm (0.4 in).

crust. Earth’s outermost layer or shell. 

cryptocrystalline. Describes a rock texture in which 

individual crystals are too small to be recognized or 

distinguished with an ordinary microscope. 

crystalline. Describes a regular, orderly, repeating geometric 

structural arrangement of atoms.
95

crystal structure. The orderly and repeated arrangement of 

atoms in a crystal.

cycad. A member of a group of seed-bearing plants 

(Cycadales) with pinnately compound leaves, poorly 

developed wood, and ovules borne on loosely or compactly 

arranged spore-bearing leaves in terminal cones. Range: late 

Carboniferous (?) to Holocene.

debris flow. A moving mass of rock fragments, soil, and mud, 

with more than half of the particles larger than sand size. 

Slow debris flows may move less than 1 m (3 ft) per year; 

rapid ones reach 160 kph (100 mph). 

deformation. The process of folding, faulting, shearing, or 

fabric development in rocks as a result of Earth stresses.

delta. The low, nearly flat, alluvial tract of land at or near 

the mouth of a river, commonly forming a triangular or 

fan-shaped plain of considerable area; resulting from 

the accumulation of sediment supplied by the river in 

such quantities that it is not removed by tides, waves, and 

currents.

delta plain. The level or nearly level surface composing the 

landward part of a large or compound delta; strictly, an 

alluvial plain characterized by repeated channel bifurcation 

and divergence, multiple distributary channels, and 

interdistributary flood basins.

dendritic. Describes a branching pattern.

desiccation. A complete or nearly complete drying-out or 

drying-up.

detrital. Pertaining to or formed from detritus.

detrital mineral. Any mineral grain resulting from mechanical 

disintegration of parent rock, especially a heavy mineral 

found in a sediment, or weathered and transported from a 

vein or lode and found in a placer or alluvial deposit.

detritus. Loose rock and mineral material that is worn off or 

removed by mechanical processes.

differential erosion. Erosion that occurs at irregular or 

varying rates due to differences in the resistance and 

hardness of surface material: softer and weaker rocks are 

rapidly worn away; harder and more resistant rocks remain 

to form ridges, hills, or mountains.

dip. The angle between a bed or other geologic surface and 

the horizontal plane.

dip-slip fault. A fault with measurable offset where the relative 

movement is parallel to the dip of the fault. 

discharge. The rate of flow of surface water or groundwater at 

a given moment, expressed as volume per unit of time.

discordant. Describes an igneous intrusion having contacts 

that are not parallel to foliation or bedding in the country 

rock.

displacement. The relative movement of the two sides of a 

fault; also, the specific amount of such movement.

dolomite (rock). A carbonate sedimentary rock containing 

more than 50% of the mineral dolomite (calciummagnesium carbonate).

dolomitic. Describes a rock containing dolomite, especially 

one that contains 5%–50% of the mineral dolomite in the 

form of cement and/or grains or crystals.

dome. Any smoothly rounded landform or rock mass; more 

specifically, an elliptical uplift in which rocks dip gently 

away in all directions. 

downcutting. Stream erosion in which cutting is directed 

primarily downward, as opposed to laterally.

drainage. The manner in which the waters of an area flow 

off in surface streams or subsurface conduits; also, the 

processes of surface drainage of water from an area by 

streamflow and sheet flow, and the removal of excess water 

from soil by downward flow.

drainage basin. A region or area bounded by a drainage divide 

and occupied by a drainage system, specifically the tract of 

country that gathers water originating as precipitation and 

contributes it to a particular stream channel or system of 

channels, or to a lake, reservoir, or other body of water.

dune. A low mound or ridge of sediment, usually sand, 

deposited by the wind. 

dune field. Extensive deposits of sand in an area where the 

supply is abundant; individual dunes resemble barchans 

dunes but are highly irregular in shape and crowded.

emergence. A change in the levels of water and land such that 

the land is relatively higher and areas formerly under water 

are exposed; results from either an uplift of land or fall of 

water level. 

entrenched meander. An incised meander carved downward 

into the surface of the valley in which the meander 

originally formed; preserves its original pattern with little 

modification, suggesting rejuvenation of a meandering 

stream as a result of rapid vertical uplift or a lowering of 

base level; exhibits a symmetric cross profile in a gorge or 

canyon setting.

ephemeral lake. A short-lived lake.

ephemeral stream. A stream that flows briefly, only in direct 

response to precipitation, and whose channel is always 

above the water table. 

erg. A regionally extensive tract of sandy desert.

erosion. The general process or group of processes that 

loosen, dissolve, wear away, and simultaneously move from 

one place to another, the materials of Earth’s crust; includes 

weathering, solution, abrasive actions, and transportation, 

but usually excludes slope movements.
96

escarpment. A steep cliff or topographic step resulting from 

vertical displacement on a fault or as a result of slope 

movement or erosion. Synonymous with “scarp.”

estuary. The seaward end or tidal mouth of a river where 

freshwater and seawater mix.

evaporite. A sedimentary rock composed primarily of 

minerals produced from a saline solution as a result of 

extensive or total evaporation of the solvent (usually water).

exfoliation. The spalling, peeling, or flaking of layers or 

concentric sheets from an exposed rock mass caused by a 

change in heat or a reduction in pressure when overlying 

rocks erode away.

extension. Deformation of Earth’s crust whereby rocks are 

pulled apart. 

extrusive. Describes an igneous rock that has been erupted 

onto the surface of the Earth. Extrusive rocks include lava 

flows and pyroclastic material such as volcanic ash.

fault. A break in rock characterized by displacement of one 

side relative to the other.

fenestral. Having openings or transparent areas in a rock.

fine-grained. Describes sediment or sedimentary rock and 

texture in which the individual constituents are too small 

to distinguish with the unaided eye, specifically sediment 

or rock whose particles have an average diameter less than 

1/16 mm (0.002 in), that is, silt-size particles and smaller. 

Also, describes a crystalline or glassy rock and texture 

in which the individual minerals are relatively small, 

specifically an igneous rock whose particles have an average 

diameter less than 1 mm (0.04 in). 

fissile. Capable of being easily split along closely spaced 

planes. 

flat slab subduction. Refers to the subduction of one tectonic 

plate beneath another at a relatively shallow angle.

floodplain. The surface or strip of relatively smooth land 

composed of alluvium and adjacent to a river channel, 

constructed by the present river in its existing regimen and 

covered with water when the river overflows its banks. A 

river has one floodplain and may have one or more terraces 

representing abandoned floodplains.

fluvial. Of or pertaining to a river or rivers.

fluvial channel. A natural passageway or depression produced 

by the action of a stream or river. 

fold. A curve or bend in an originally flat structure, such as a 

rock stratum, bedding plane, or foliation; usually a product 

of deformation.

foliation. A preferred arrangement of crystal planes in 

minerals. Primary foliation develops during the formation 

of a rock and includes bedding in sedimentary rocks and 

flow layering in igneous rocks. In metamorphic rocks, the 

term commonly refers to a parallel orientation of planar 

minerals such as micas. Secondary foliation develops during 

deformation and/or metamorphism and includes cleavage, 

schistosity, and gneissic banding.

footwall. The lower wall of a fault. 

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, and 

has definable upper and lower contacts.

fossil. A remain, trace, or imprint of a plant or animal that has 

been preserved in the Earth’s crust since some past geologic 

time; loosely, any evidence of past life.

fracture. The breaking of a mineral other than along planes of 

cleavage. Also, any break in a rock such as a crack, joint, or 

fault.

freeze-thaw. The mechanical weathering process caused 

by alternate or repeated cycles of freezing and thawing 

water in pores, cracks, and other openings of rock and 

unconsolidated deposits, usually at the surface. 

friable. Describes a rock or mineral that is easily crumbled. 

frost wedging. A type of mechanical disintegration, splitting, 

or breakup of a rock by which jointed rock is pried and 

dislodged by ice acting as a wedge.

gastropod. Any mollusk belonging to the class Gastropoda, 

characterized by a distinct head with eyes and tentacles 

and, in most, by a single calcareous shell that is closed at the 

apex, sometimes spiraled, not chambered, and generally 

asymmetrical. Range: Upper Cambrian to Holocene. 

gradient. A degree of inclination (steepness of slope), or a 

rate of ascent or descent, of an inclined part of Earth’s 

surface with respect to the horizontal; expressed as a ratio 

(vertical to horizontal), a fraction (such as m/km or ft/mi), a 

percentage (of horizontal distance), or an angle (in degrees).

grainstone. A mud-free (less than 1% of material with 

diameter less than 20 micrometers), grain-supported, 

carbonate sedimentary rock.

gravel. An unconsolidated, natural accumulation of typically 

rounded rock fragments resulting from erosion; consists 

predominantly of particles larger than sand; that is, greater 

than 2 mm (1/12 in) across.

groundmass. The finer grained and/or glassy material between 

the large crystals of an igneous rock. Also, sometimes used 

for the matrix of a sedimentary rock.

groundwater. That part of subsurface water that is in the zone 

of saturation, including underground streams.

gypsum. A sulfate (sulfur + oxygen) mineral of calcium and 

water, CaSO4

 • 2H2O.
97

hanging wall. The upper wall of a fault. 

hematite. An oxide mineral composed of oxygen and iron, 

Fe2O3.

heterogeneous. Consisting of dissimilar or diverse 

ingredients or constituents.

homogeneous. Of uniform structure or composition 

throughout.

hoodoo. A bizarrely shaped column, pinnacle, or pillar of 

rock, commonly produced in a region of sporadic heavy 

rainfall by differential weathering or erosion of horizontal 

strata, facilitated by layers of varying hardness and joints.

ichnofossil. A trace fossil such as a fossil footprint, track, or 

burrow.

igneous. Describes a rock or mineral that solidified from 

molten or partly molten material; also, describes processes 

leading to, related to, or resulting from the formation 

of such rocks. One of the three main classes or rocks—

igneous, metamorphic, and sedimentary.

imbrication. Consistent orientation of rocks or their clasts; 

commonly displayed by pebbles on a stream bed that have 

been tilted by flowing water so that their flat surfaces dip 

upstream.

incision. Downward erosion by a stream, resulting in a 

deepened channel and commonly a narrow, steep-walled 

valley.

indurated. Describes a rock or soil hardened or consolidated 

by pressure, cementation, or heat.

induration. Hardening by heat, pressure, or the introduction 

of cementing material, especially the process by which 

relatively consolidated rock is made harder or more 

compact.

interdune. The relatively flat surface between dunes, 

commonly a long, troughlike, wind-swept passage between 

parallel dunes; may be covered with sand or sand free.

intrusion. The process of emplacement of magma into 

preexisting rock. Also, the igneous rock mass formed. 

intrusive. Pertaining to intrusion, both the process and the 

rock body.

island arc. A offshore, generally curved belt of volcanoes 

above a subduction zone.

isotopic age. An age (in years) calculated from the quantitative 

determination of radioactive elements and their decay 

products.

isotopic dating. Calculating an age in years for geologic 

materials by measuring the presence of a short-lived 

radioactive element (e.g., carbon-14) or by measuring the 

presence of a long-lived radioactive element plus its decay 

product (e.g., potassium-40/argon-40). The term applies to 

all methods of age determination based on nuclear decay of 

naturally occurring radioactive isotopes.

joint. A break in rock without relative movement of rocks on 

either side of the fracture surface.

karst. A type of topography that is formed on limestone, 

gypsum, and other soluble rocks, primarily by dissolution. 

It is characterized by sinkholes, caves, and underground 

drainage.

laccolith. A mushroom-shaped pluton that has intruded 

sedimentary strata and domed up the overlying sedimentary 

layers. 

lacustrine. Describes a process, feature, or organism 

pertaining to, produced by, or inhabiting a lake.

lag gravel. An accumulation of coarse material remaining on a 

surface after finer material has been blown or washed away.

lagoon. A narrow body of water that is parallel to the 

shore and between the mainland and a barrier island; 

characterized by minimal or no freshwater influx and 

limited tidal flux, which cause elevated salinities. Also, a 

shallow body of water enclosed or nearly enclosed within 

an atoll.

landslide. A collective term covering a wide variety of 

slope-movement landforms and processes that involve the 

downslope transport of soil and rock material en masse 

under the influence of gravity.

left-lateral fault. A strike-slip fault on which the side opposite 

the observer has been displaced to the left. Synonymous 

with “sinistral fault.”

lens. A sedimentary deposit that resembles a convex lens and 

is characterized by converging surfaces, thick in the middle 

and thinning out toward the edges.

lenticular. Resembling in shape the cross section of a lens.

limb. One side of a structural fold.

limestone. A carbonate sedimentary rock consisting of more 

than 95% calcite and less than 5% dolomite.

lithification. The conversion of sediment into solid rock.

lithify. To change to stone, especially to consolidate from a 

loose sediment to a solid rock. 

lithofacies. A lateral, mappable subdivision of a designated 

stratigraphic unit distinguished from adjacent subdivisions 

on the basis of lithology.
98

lithology. The physical description or classification of a rock 

or rock unit based on characteristics such as color, mineral 

composition, and grain size.

loess. Windblown silt-sized sediment.

losing stream. A stream that loses water or disappears as it 

flows downstream. The water infiltrates into the ground or 

into underground void spaces.

lower flow regime. A condition of stream flow that is 

characterized by a unidirectional current and relatively low 

sediment transport rates. 

magma. Molten rock beneath Earth’s surface capable of 

intrusion and extrusion. 

marker bed. A well-defined, easily identifiable stratum or 

body of strata that has sufficiently distinctive characteristics 

(such as lithology or fossil content) to facilitate correlation 

in field mapping or subsurface work. Also, a geologic 

formation that serves as a marker.

mass wasting. Dislodgement and downslope transport of 

a mass of rock and/or unconsolidated material under the 

direct influence of gravity. In contrast to “erosion,” the 

debris removed is not carried within, on, or under another 

medium. Synonymous with “slope movement.”

meander. One of a series of sinuous curves, bends, or turns 

in the course of a stream, produced by a mature stream 

swinging from side to side as it flows across its floodplain 

or shifts its course laterally toward the convex side of an 

original curve.

mechanical weathering. The physical breakup of rocks 

without change in composition. 

medium-grained. Describes an igneous rock and texture 

in which the individual crystals have an average diameter 

in the range of 1 to 5 mm (0.04 to 0.2 in.). Also, describes 

sediment or sedimentary rock and texture in which the 

individual particles have an average diameter in the range of 

1/16 to 2 mm (0.002 to 0.08 in), that is, sand size.

member. A lithostratigraphic unit with definable contacts; a 

subdivision of a formation.

mesa. A broad, flat-topped erosional hill or mountain with by 

steeply sloping sides or cliffs.

metamorphic rock. Any rock derived from preexisting 

rocks that was altered in response to marked changes 

in temperature, pressure, shearing stress, and chemical 

environment. One of the three main classes of rock—

igneous, metamorphic, and sedimentary.

micrite. A descriptive term for the semiopaque crystalline 

matrix of limestones, consisting of carbonate mud and 

interpreted as a lithified ooze.

mineral. A naturally occurring inorganic crystalline solid with 

a definite chemical composition or compositional range.

mold. An impression made in the surrounding earth by 

the exterior or interior of a fossil shell or other organic 

structure and then preserved. Also, a cast of the inner 

surface of a fossil shell.

monocline. A one-limbed fold in strata that are otherwise 

flat-lying.

monument. An isolated pinnacle, column, or pillar of rock 

resulting from erosion that resembles a human-made 

monument or obelisk.

montmorillonite. A clay mineral of the smectite group, which 

is common in soils, sedimentary rocks, and some mineral 

deposits. Smectite minerals are derived from the alteration 

of volcanic glass and the weathering of primary silicates. 

mud crack. A crack formed in clay, silt, or mud by shrinkage 

during dehydration at Earth’s surface.

mudstone (carbonate sedimentary rock). A carbonate 

mud-supported sedimentary rock containing less than 

10% grains (particles with diameters greater than 20 

micrometers). 

mudstone (clastic sedimentary rock). An indurated mud 

having the texture and composition of shale, but lacking its 

fine lamination or fissility.

normal fault. A fault in which the hanging wall appears to 

have moved downward relative to the footwall; the angle of 

dip is usually 45°–90°. 

oil field. A geographic region rich in petroleum resources 

and containing one or more wells that produce, or have 

produced, oil and/or gas.

ooid. An individual spherite or an oolitic rock; an oolith.

oolite. A sedimentary rock, usually a limestone, made up 

chiefly of ooliths cemented together.

oolith. One of the small round or ovate accretionary bodies in 

a sedimentary rock, resembling the roe of fish, and having 

diameters of 0.25–2 mm (0.01–0.08 in).

orogeny. A mountain-building event.

outcrop. Any part of a rock mass or formation that is exposed 

or “crops out” at Earth’s surface. 

outwash. Glacial sediment transported and deposited by 

meltwater streams.

packstone. A sedimentary carbonate rock whose granular 

material is arranged in a self-supporting framework, yet also 

contains some matrix of calcareous mud.

paleogeography. The study, description, and reconstruction 

of the physical landscape in past geologic periods.

paleontology. The study of the life and chronology of Earth’s 

geologic past based on the fossil record.

paleosol. An soil layer preserved in the geologic record.
99

Pangea. A supercontinent that existed from about 300 million 

to about 200 million years ago and included most of the 

continental crust of the Earth, from which the present 

continents were derived by fragmentation and continental 

drift. During an intermediate stage of the fragmentation—

between the existence of Pangea and that of the present 

continents—Pangea split into two large fragments, Laurasia 

in the Northern Hemisphere and Gondwana in the 

Southern Hemisphere.

parent material. The unconsolidated organic and mineral 

material from which soil forms.

parent rock. Rock from which soil, sediment, or other rock is 

derived.

passive margin. A continental plate boundary where no platescale tectonism is taking place; plates are not converging, 

diverging, or sliding past one another.

peat. An accumulation of partly decomposed plant remains 

in swampy lowlands. It is an early stage or rank in the 

development of coal.

pebble. A small rounded rock, especially a waterworn stone, 

between 4 and 64 mm (0.16 and 2.5 in) across.

pediment. A gently sloping, erosional bedrock surface at the 

foot of a mountain or plateau escarpment.

pelecypod. Any benthic aquatic mollusk belonging to the 

class Pelecypoda, characterized by a bilaterally symmetrical 

bivalve shell, a hatchet-shaped foot, and sheetlike gills. 

Range: Ordovician to Holocene.

peloid. An allochem composed of micrite (carbonate mud), 

irrespective of size or origin, for which exact origin is 

unknown.

period. The fundamental unit of the worldwide geologic time 

scale. It is lower in rank than era and higher than epoch. 

The geochronologic unit during which the rocks of the 

corresponding system were formed.

permeability. A measure of the relative ease with which a fluid 

moves through the pore spaces of a rock or unconsolidated 

deposit.

pictograph. A picture painted on a rock by primitive peoples.

piedmont. A gently sloping area at the base of a mountain 

front. Synonymous with “bajada.” Also, describes a feature 

(e.g., plain, slope, or glacier) that lies or formed at the base 

of a mountain or mountain range.

piping. Erosion or solution by percolating water in a layer 

of subsoil, resulting in the formation of narrow conduits, 

tunnels, or “pipes” through which soluble or granular soil 

material is removed.

placer. A concentrated deposit of minerals, usually heavy, such 

as gold, cassiterite, or rutile, in a beach or stream deposit. 

placer mining. The extraction of metals or minerals from 

placers, usually involves running water.

plate tectonics. A theory of global tectonics in which the 

lithosphere is divided into about 20 rigid plates that interact 

with one another at their boundaries, causing seismic and 

tectonic activity along these boundaries.

plateau. A broad, flat-topped topographic high (terrestrial or 

marine) of great extent and elevation above the surrounding 

plains, canyons, or valleys.

playa. A dry, vegetation-free, flat area at the lowest part of an 

undrained desert basin.

playa lake. A shallow, intermittent lake in an arid region, 

covering up or occupying a playa in the wet season but 

subsequently drying up.

porosity. The percentage of total void space in a volume of 

rock or unconsolidated deposit.

Precambrian. A commonly used term to designate all rocks 

older than the Cambrian Period of the Standard Global 

Chronostratigraphic Scale. It includes the Archean and 

Proterozoic eons and represents 90% of geologic time.

quartz. Silicon dioxide, SiO2. The only silicate (silicon + 

oxygen) mineral consisting entirely of silicon and oxygen. 

Synonymous with “crystalline silica.”

radioactivity. The spontaneous decay or breakdown of 

unstable atomic nuclei.

radiocarbon age. An isotopic age expressed in years and 

calculated from the quantitative determination of the 

amount of carbon-14 remaining in an organic material. 

Synonymous with “carbon-14 age.”

radiometric age. An age (in years) calculated from the 

quantitative determination of radioactive elements and their 

decay products. The preferred term is “isotopic age.”

red bed. Sedimentary strata that is predominantly red due 

to the presence of ferric iron oxide (hematite) coating 

individual grains; usually sandstone, siltstone, or shale.

regolith. From the Greek “rhegos” (blanket) + “lithos” 

(stone), the layer of unconsolidated rock material that forms 

the surface of the land and overlies or covers bedrock; 

includes rock debris of all kinds, volcanic ash, glacial drift, 

alluvium, loess, and eolian deposits, vegetal accumulations, 

and soil.

regression. Long-term seaward retreat of the shoreline or 

relative fall of sea level.

relative dating. The chronological placement and ordering 

of rocks, events, or fossils with respect to the geologic time 

scale and without reference to numerical ages.

reverse fault. A contractional high-angle (greater than 45°) 

dip-slip fault in which the hanging wall moves up relative to 

the footwall. 
100

right-lateral fault. A strike-slip fault on which the side 

opposite the observer has been displaced to the right. 

rincon. Meaning “inside corner or nook” in Spanish and used 

in the southwestern United States for a square-cut recess 

or hollow in a cliff or a reentrant in the borders of a mesa 

or plateau. Also used for a small, secluded valley, and for a 

bend in a stream. 

ripple marks. The undulating, approximately parallel and 

usually small-scale pattern of ridges formed in sediment by 

the flow of wind or water.

rock. An aggregate of one or more minerals (e.g., granite), a 

body of undifferentiated mineral matter (e.g., obsidian), or a 

body of solid organic material (e.g., coal).

rockfall. The most rapid type of slope movement in which a 

newly detached fragment of bedrock of any size falls from a 

cliff or other very steep slope, traveling straight down or in a 

series of leaps and bounds down a slope.

roundness. The relative amount of curvature of the “corners” 

of a sediment grain.

sabkha. Any flat area, either coastal or interior, where saline 

minerals crystallize near or at the surface as a result of 

deflation or evaporation. 

sand. A clastic particle smaller than a granule and larger than 

a silt grain, with a diameter ranging from 1/16 to 2 mm 

(0.0025 to 0.08 in).

sand sheet. A sheetlike body of surficial sediment, commonly 

sand, that veneers the underlying stratigraphic units 

(unconsolidated deposits or bedrock) and can range in 

thickness from a few centimeters to tens of meters, with a 

lateral persistence of a few meters to tens of kilometers.

sandstone. Clastic sedimentary rock composed of 

predominantly sand-sized grains.

scarp. A steep cliff or topographic step resulting from 

displacement on a fault or as a result of slope movement or 

erosion. Synonymous with “escarpment.”

scour. The powerful and concentrated clearing and digging 

action of flowing water, air, or ice.

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary. Pertaining to or containing sediment. 

sedimentary rock. A rock resulting from the consolidation 

of loose sediment that has accumulated in layers; it may 

be “clastic,” consisting of mechanically formed fragments 

of older rock; “chemical,” formed by precipitation from 

solution; or “organic,” consisting of the remains of plants 

and animals. One of the three main classes of rock—

igneous, metamorphic, and sedimentary. 

sedimentation. The process of forming or accumulating 

sediment into layers, including the separation of rock 

particles from parent rock, the transportation of these 

particles to the site of deposition, the actual deposition or 

settling of the particles, the chemical and other changes 

occurring in the sediment, and the ultimate consolidation of 

the sediment into solid rock. 

seismic. Pertaining to an earthquake or Earth vibration, 

including those that are artificially induced.

seismicity. The phenomenon of movements in the Earth’s 

crust. Synonymous with “seismic activity.”

shale. A clastic sedimentary rock made of clay-sized particles 

and characterized by fissility.

siliciclastic. Describes noncarbonate clastic rocks.

siliceous. Describes a rock or other substance containing 

abundant silica.

sill. An igneous intrusion that parallels the bedding of 

preexisting sedimentary rock or the foliation of preexisting 

metamorphic rock.

silt. Clastic sedimentary material intermediate in size between 

fine-grained sand and coarse clay, 0.0039 to 0.063 mm 

(0.00015 to 0.0025 in) across.

siltstone. A clastic sedimentary rock composed of silt-sized 

grains.

slip face. The steeply sloping surface on the lee side of a dune, 

standing at or near the angle of repose of loose sand, and 

advancing downwind by a succession of slides wherever 

that angle is exceeded.

slope. The inclined surface of any part of Earth’s surface, such 

as a hillslope. Also, a broad part of a continent descending 

into an ocean.

slope movement. The gradual or rapid downslope movement 

of soil or rock under gravitational stress. Synonymous with 

“mass wasting.”

slope wash. Soil and rock material that is or has been 

transported down a slope under the force of gravity and 

assisted by running water not confined to channels; also, the 

process by which slope-wash material is moved.

slump. A generally large, coherent slope movement with a 

concave failure surface and subsequent backward rotation 

relative to the slope.

smectite. A group of expanding-lattice clay minerals 

derived from the alteration of volcanic glass and from the 

weathering of primary silicates.

soil. The unconsolidated portion of the Earth’s crust modified 

through physical, chemical, and biotic processes into a 

medium capable of supporting plant growth.
101

sorted. Describes an unconsolidated sediment consisting of 

particles of essentially uniform size.

sorting. The dynamic process by which sedimentary particles 

having some particular characteristic (such as similarity of 

size, shape, or specific gravity) are naturally selected and 

separated from associated but dissimilar particles by the 

agents of transportation.

spalling. The process by which scales, plates, or flakes of 

rock, from less than a centimeter to several meters thick, 

successively fall from the bare surface of a large rock mass; a 

form of exfoliation.

spicules. One of the numerous minute calcareous or siliceous 

bodies, having highly varied and often characteristic forms, 

occurring in and serving to stiffen and support the tissues 

of various invertebrates, and frequently found in marinesediment samples and in Paleozoic and Cretaceous chert. 

Example: a discrete, needle-like skeletal element of a 

sponge.

spring. A place where groundwater flows naturally from a 

rock or the soil onto the land surface or into a body of 

surface water. 

strata. Tabular or sheetlike layers of sedimentary rock that are 

visually distinctive from other layers above and below. The 

singular form of the term is stratum, but is less commonly 

used.

stratification. The accumulation or layering of sedimentary 

rocks as strata. Tabular, or planar, stratification refers to 

essentially parallel surfaces. Cross-stratification refers to 

strata inclined at an angle to the main stratification.

stratigraphy. The geologic study of the origin, occurrence, 

distribution, classification, correlation, and age of rock 

layers, especially sedimentary rocks.

stream. Any body of water moving under gravity flow in a 

clearly confined channel.

stream capture. The natural diversion of the headwaters 

of one stream into the channel of another stream having 

greater erosional activity. Synonymous with “stream piracy.”

stream channel. A long, narrow depression shaped by the 

concentrated flow of stream water.

stream terrace. A planar surface alongside a stream valley 

representing the remnants of an abandoned floodplain, 

stream bed, or valley floor produced during a former stage 

of erosion or deposition.

strike. The compass direction of the line of intersection of an 

inclined surface with a horizontal plane.

strike-slip fault. A fault with measurable offset where the 

relative movement is parallel to the strike of the fault. 

Described as left-lateral (sinistral) when relative motion of 

the block opposite the observer is to the left, and rightlateral (dextral) when relative motion is to the right. 

stromatolite. An sedimentary structure produced by 

sediment trapping, binding, and/or precipitation as a result 

of the growth and metabolic activity of microorganisms, 

principally cyanophytes (blue-green algae); occurs in 

a variety of forms, from nearly horizontal to markedly 

columnar, domal, or subspherical.

structural geology. The branch of geology that deals with 

the description, representation, and analysis of structures, 

primarily on a moderate to small scale. The subject is similar 

to tectonics, but the latter term is generally used for the 

analysis of broader regional or historical phases.

structure. The attitudes and relative positions of the rock 

masses of an area resulting from such processes as faulting, 

folding, and igneous intrusion.

subduction. The process of one lithospheric plate descending 

beneath another.

subduction zone. A long, narrow belt in which subduction 

takes place.

submarine. Something situated or living under the surface of 

the sea.

subsidence. The sudden sinking or gradual downward settling 

of part of Earth’s surface.

suture. The linear zone where two continental landmasses 

become joined via obduction.

syncline. A generally concave upward fold of which the core 

contains the stratigraphically younger rocks. 

system (stratigraphy). The fundamental unit of 

chronostratigraphic classification of Phanerozoic rocks; 

each unit represents a time span and an episode of Earth 

history sufficiently great to serve as a worldwide reference 

unit. It is the temporal equivalent of a period. 

talus. Rock fragments, usually coarse and angular, lying at the 

base of a cliff or steep slope from which they have fallen.

tectonic. Describes a feature or process related to large-scale 

movement and deformation of Earth’s crust.

tectonics. The geologic study of the broad structural 

architecture and deformational processes of the lithosphere 

and asthenosphere.

terrace. Any long, narrow, relatively level or gently inclined 

surface (i.e., a bench or steplike ledge) that is bounded 

along one edge by a steeper descending slope and along the 

other edge by a steeper ascending slope, thus breaking the 

continuity of the slope; commonly occurs along the margin 

and above the level of a body of water, marking a former 

water level.

terrestrial. Describes a feature, process, or organism related to 

land, Earth, or its inhabitants.

terrigenous. Describes material or a feature derived from the 

land or a continent.
102

thrust fault. A dip-slip fault with a shallowly dipping (less 

than 45°) fault surface where the hanging wall moves up and 

over relative to the footwall. 

topography. The general morphology of Earth’s surface, 

including relief and locations of natural and human-made 

features.

trace fossil. A fossilized feature such as a track, trail, 

burrow, or coprolite (dung), that preserves evidence of an 

organism’s life activities, rather than the organism itself. 

Compare to “body fossil.”

transform fault. A strike-slip fault that links two other faults 

or plate boundaries such as two segments of a mid-ocean 

ridge. 

transgression. Landward migration of the sea as a result of a 

relative rise in sea level.

trend. The direction or bearing of an outcrop of a geologic 

feature such as an ore body, fold, or orogenic belt.

trilobite. Any marine arthropod belonging to the class 

Trilobita, characterized by a three-lobed ovoid outer 

skeleton, divided lengthwise into axial and side regions and 

transversely into cephalon (“head”), thorax (middle), and 

pygidium (“tail”). Range: Lower Cambrian to Permian.

tufa. A chemical sedimentary rock composed of calcium 

carbonate, formed by evaporation commonly as an 

incrustation around the mouth of a spring, along a stream, 

or less commonly as a thick, concretionary deposit in a lake 

or along its shore. It may also be precipitated by algae or 

bacteria. The hard, dense variety of travertine.

type locality. The place where a geologic feature such as an 

ore occurrence, a particular kind of igneous rock, or the 

type specimen of a fossil species was first recognized and 

described.

type section. The originally described sequence of strata 

that constitute a stratigraphic unit. It serves as an objective 

standard with which spatially separated parts of the unit 

may be compared. It is preferably in an area where the unit 

shows maximum thickness and is completely exposed (or at 

least shows top and bottom).

unconformable. Describes strata that do not succeed the 

underlying rocks in immediate order of age or in parallel 

position, especially younger strata that do not have the same 

dip and strike as the underlying rocks. Also, describes the 

contact between unconformable rocks.

unconformity. A substantial break or gap in the geologic 

record where a rock unit is overlain by another that is not 

next in stratigraphic succession, resulting from either a 

change that caused deposition to cease for a considerable 

span of time or erosion with loss of the previously formed 

record.

undercutting. The removal of material at the base of a steep 

slope by the erosive action of water (such as a meandering 

stream), sand-laden wind in a desert, or waves along a coast.

uplift. A structurally high area in Earth’s crust produced by 

movement that raises the rocks.

upper flow regime. A condition of stream flow that is 

characterized by a unidirectional current and relatively high 

sediment transport rates.

vesicle. A cavity of variable shape formed by the entrapment 

of a gas bubble during solidification of lava.

vesicular. Describes the texture of a rock, especially lava, 

characterized by abundant vesicles formed as a result of the 

expansion of gases during the fluid stage of a lava.

volcanic. Pertaining to the activities, structures, or rock types 

of a volcano. A synonym of extrusive.

wackestone. A term for a mud-supported carbonate 

sedimentary rock containing more than 10% grains 

(particles with diameters greater than 20 micrometers).

wash. A broad, gravelly, dry stream bed, generally in the 

bottom of a canyon that is periodically swept by a torrent 

of water. The term is used especially in the southwestern 

United States.

weathering. The physical, chemical, and biological processes 

by which rock is broken down, particularly at Earth’s 

surface.
103

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Basin, Utah, Colorado, New Mexico, and Arizona. The Mountain Geologist 51(2):119–138.

Wieczorek, G. F., and J. B. Snyder. 2009. Monitoring slope movements. Pages 245–271 in R. Young and L. Norby, editors. Geological 

monitoring. Geological Society of America, Boulder, Colorado. http://go.nps.gov/monitor_slopes (accessed 30 April 2015).

Wild Backpacker. 2015. Coyote Gulch. http://www.wildbackpacker.com/backpacking-trails/coyote-gulch/ (accessed 4 February 

2015).

Wilkens, N. D., J. D. Farmer, and K. B. Pigg. 2005. Exceptional paleobotanical remains preserved in Navajo Sandstone interdune 

deposits near Moab, Utah. Geological Society of America Abstracts with Programs 37(7):527–528. 

Wilkens, N. D., J. D. Farmer, and K. B. Pigg. 2007. Paleoecology of Jurassic Navajo Sandstone interdune environments: an integrated 

view based on sedimentology, geochemistry, and paleontology. Geological Society of America Abstracts with Programs 39(6):434.

Willis, G. C. 1992. Lava Creek “B” volcanic ash in pediment mantle deposits, Colorado Plateau, east central Utah—implications 

for Colorado River downcutting and pedogenic carbonate accumulation rates. Geological Society of Abstracts with Program 

24(6):68.

Willis, G. C. 2004. Interim geologic map of the lower San Juan River area, eastern Glen Canyon National Recreation Area and 

vicinity, San Juan County, Utah (scale 1:50,000). Open-File Report 443DM. Utah Geological Survey, Salt Lake City, Utah.

Willis, G. C. 2010a. Geologic map of the Glen Canyon Dam area, Glen Canyon National Recreation Area, Arizona and Utah (scale 

1:24,000). Miscellaneous Publication (GIS data). Utah Geological Survey, Salt Lake City, Utah.

Willis, G. C. 2010b. Geologic map of the Hite Crossing— lower Dirty Devil River area, Glen Canyon National Recreation Area, 

Garfield and San Juan Counties, Utah (scale 1:50,000). Utah Geological Survey Map (GIS data), Salt Lake City, Utah.

Willis, G. C., and R. F. Biek. 2001. Quaternary incision rates of the Colorado River and major tributaries in the Colorado Plateau, 

Utah. Pages 119–124 in R. A. Young and E. E. Spamer, editors. Colorado River origin and evolution: Grand Canyon, Arizona. 

Symposium Volume. Grand Canyon Association, Grand Canyon, Arizona. 

Willis, G.C., and J. B. Ehler. in preparation. Interim geologic map of Glen Canyon National Recreation Area and vicinity, San Juan, 

Kane, Garfield, Wayne and Grand Counties, Utah and Coconino County, Arizona (scale 1:24,000 to 1:100,000). Open-File 

Report. Utah Geological Survey, Salt Lake City, Utah.

Young, R. and L. Norby, editors. 2009. Geological monitoring. Geological Society of America, Boulder, Colorado. http://go.nps.gov/

geomonitoring (accessed 29 February 2016).
117

Additional References

This chapter lists additional references, resources, and websites that may be of use to resource 

managers. Web addresses are valid as of June 2016. Refer to Appendix B for laws, regulations, and 

policies that apply to NPS geologic resources.

Geology of National Park Service Areas

● NPS Geologic Resources Division (Lakewood, 

Colorado) Energy and Minerals; Active Processes 

and Hazards; Geologic Heritage:

http://go.nps.gov/geology

● NPS Geologic Resources Division Education 

Website: http://go.nps.gov/geoeducation

● NPS Geologic Resources Inventory:

http://go.nps.gov/gri

● NPS Geoscientists-in-the-Parks (GIP) internship 

and guest scientist program: http://go.nps.gov/gip

● NPS Views program (geology-themed modules are 

available for Geologic Time, Paleontology, Glaciers, 

Caves and Karst, Coastal Geology, Volcanoes, and a 

variety of geologic parks): http://go.nps.gov/views

● USGS Geology of National Parks (including 3D 

imagery): http://3dparks.wr.usgs.gov/

NPS Resource Management Guidance and 

Documents

● Management Policies 2006 (Chapter 4: Natural 

resource management):

http://www.nps.gov/policy/mp/policies.html

● 1998 National parks omnibus management act: 

http://www.gpo.gov/fdsys/pkg/PLAW-105publ391/

pdf/PLAW-105publ391.pdf

● NPS-75: Natural resource inventory and 

monitoring guideline:

http://www.nature.nps.gov/nps75/nps75.pdf

● NPS Natural resource management reference 

manual #77: http://www.nature.nps.gov/Rm77/

● Geologic monitoring manual (Young and Norby 

2009): http://go.nps.gov/geomonitoring

● NPS Technical Information Center (TIC) (Denver, 

Colorado; repository for technical documents): 

http://www.nps.gov/dsc/technicalinfocenter.htm

Climate Change Resources

● NPS Climate Change Response Program Resources: 

http://www.nps.gov/subjects/climatechange/

resources.htm

● US Global Change Research Program:

http://globalchange.gov/home

● Intergovernmental Panel on Climate Change:

http://www.ipcc.ch/

Geological Surveys and Other Organizations

● Arizona Geological Survey: http://www.azgs.az.gov/ 

● Utah Geological Association:

http://www.utahgeology.org/

● Utah Geological Survey: http://geology.utah.gov/

● US Geological Survey: http://www.usgs.gov/

● Geological Society of America:

http://www.geosociety.org/

● American Geophysical Union: http://sites.agu.org/

● American Geosciences Institute:

http://www.americangeosciences.org/

● Association of American State Geologists:

http://www.stategeologists.org/

US Geological Survey Reference Tools

● National geologic map database (NGMDB):

http://ngmdb.usgs.gov/

● Geologic names lexicon (GEOLEX; geologic unit 

nomenclature and summary):

http://ngmdb.usgs.gov/Geolex/geolex_home.html

● Geographic names information system (GNIS; 

official listing of place names and geographic 

features): http://gnis.usgs.gov/

● GeoPDFs (download searchable PDFs of any 

topographic map in the United States):

http://store.usgs.gov (click on “Map Locator”)

● Publications warehouse (many publications 

available online): http://pubs.er.usgs.gov

● Tapestry of time and terrain (descriptions of 

physiographic provinces):

http://pubs.usgs.gov/imap/i272

119

Appendix A: Scoping Participants

The following people attended the GRI scoping meeting for Glen Canyon National Recreation Area, 

held on 23–25 September 1999, or the follow-up report writing conference call, held on 5 March 2015. 

Discussions during these meetings supplied a foundation for this GRI report. The scoping summary 

document is available on the GRI publications website: http://go.nps.gov/gripubs.

1999 Scoping Meeting Participants

Name Affiliation Position

Mark Anderson NPS Glen Canyon National Recreation Area Aquatic Ecologist

Pete Biggam NPS, Natural Resources Information Division Geologist

George Billingsley USGS-Flagstaff, AZ Geologist

Ben Bobowski NPS Glen Canyon National Recreation Area Rangeland Management Specialist

Lewis Boobar NPS Glen Canyon National Recreation Area Aquatic Ecologist

Tom Chidsey Utah Geological Association Geologist

Tim Connors NPS Geologic Resources Division Geologist

Joe Gregson NPS Natural Resources Information Division Geologist

Bruce Heise NPS Geologic Resources Division Geologist

Norm Henderson NPS Glen Canyon National Recreation Area Research Coordinator

Lex Newcomb NPS Glen Canyon National Recreation Area GIS Specialist

Pete Peterson

Vincent Santucci

John Spence

Doug Sprinkel

Christine Turner

Grant Willis

USGS-Denver, CO Geologist

NPS Geologic Resources Division, Fossil Butte National Monument, 

Wyoming Paleontologist

NPS Glen Canyon National Recreation Area Chief Scientist and Terrestrial Natural 

Resources Branch Chief

Utah Geological Association Geologist

USGS-Denver, CO Geologist

Utah Geological Survey Geologist

2015 Conference Call Participants

Name Affiliation Position

Tim Connors NPS Geologic Resources Division Geologist

Sarah Doyle NPS Glen Canyon National Recreation Area Physical Scientist

John Graham Colorado State University Geologist

Jason Kenworthy NPS Geologic Resources Division Geologist, GRI reports coordinator

Tyler Knudsen Utah Geological Survey Geologist

John Spence NPS Glen Canyon National Recreation Area Chief Scientist and Terrestrial Natural 

Resources Branch Chief

Grant Willis Utah Geological Survey Geologist; Mapping Program Manager

121

Appendix B: Geologic Resource Laws, Regulations, and Policies

The NPS Geologic Resources Division developed this table to summarize laws, regulations, and 

policies that specifically apply to NPS minerals and geologic resources. The table does not include 

laws of general application (e.g., Endangered Species Act, Clean Water Act, Wilderness Act, National 

Environmental Policy Act, or National Historic Preservation Act). The table does include the NPS 

Organic Act when it serves as the main authority for protection of a particular resource or when other, 

more specific laws are not available. Information is current as of June 2016. Contact the NPS Geologic 

Resources Division for detailed guidance.

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Paleontology

National Parks Omnibus Management 

Act of 1998, 54 USC § 100701 protects 

the confidentiality of the nature and 

specific location of paleontological 

resources and objects

Paleontological Resources Preservation 

Act of 2009, 16 USC § 470aaa et 

seq. provides for the management and 

protection of paleontological resources on 

federal lands

36 CFR § 2.1(a)(1)(iii) prohibits destroying, 

injuring, defacing, removing, digging or 

disturbing paleontological specimens or 

parts thereof

Prohibition in 36 CFR § 13.35 applies 

even in Alaska parks, where the surface 

collection of other geologic resources is 

permitted

Regulations in association with 2009 PRPA 

are being finalized (June 2016)

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity

Section 4.8.2.1 emphasizes Inventory and 

Monitoring, encourages scientific research, 

directs parks to maintain confidentiality of 

paleontological information, and allows 

parks to buy fossils only in accordance with 

certain criteria

Rocks and Minerals

National Parks Omnibus Management 

Act of 1998, 54 USC § 100701 protects 

the confidentiality of the nature and 

specific location of paleontological 

resources and objects

Exception: 16 USC. § 445c (c) – 

Pipestone National Monument 

enabling statute. Authorizes American 

Indian collection of catlinite (red pipestone)

36 C.F.R. § 2.1 prohibits possessing, 

destroying, disturbing mineral resources...

in park units

Exception: 36 C.F.R. § 7.91 allows limited 

gold panning in Whiskeytown

Exception: 36 C.F.R. § 13.35 allows some 

surface collection of rocks and minerals 

in some Alaska parks (not Klondike 

Gold Rush, Sitka, Denali, Glacier Bay, 

and Katmai) by non-disturbing methods 

(e.g., no pickaxes), which can be stoppe

by superintendent if collection causes 

significant adverse effects on park 

resources and visitor enjoyment

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity

Caves and Karst Systems

Federal Cave Resources Protection Act 

of 1988, 16 USC §§ 4301 – 4309 requires 

Interior/Agriculture to identify “significant 

caves” on Federal lands, regulate/

restrict use of those caves as appropriate, 

and include significant caves in land 

management planning efforts. Imposes

civil and criminal penalties for harming 

a cave or cave resources. Authorizes

Secretaries to withhold information about 

specific location of a significant cave from 

a Freedom of Information Act (FOIA) 

requester.

National Parks Omnibus Management 

Act of 1998, 54 USC § 100701 protects 

the confidentiality of the nature and 

specific location of cave and karst 

resources

36 CFR § 2.1 prohibits possessing/ 

destroying/disturbing...cave resources...in 

park units

43 CFR Part 37 states that all NPS caves 

are “significant” and sets forth procedures 

for determining/releasing confidential 

information about specific cave locations to 

a FOIA requester

Section 4.8.1.2 requires NPS to maintain 

karst integrity, minimize impacts

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity

Section 4.8.2.2 requires NPS to protect 

caves, allow new development in or on 

caves if it will not impact cave environment, 

and to remove existing developments if 

they impair caves

Section 6.3.11.2 explains how to manage 

caves in/adjacent to wilderness
122

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Upland and Fluvial Processes

Rivers and Harbors Appropriation 

Act of 1899, 33 USC § 403 prohibits the 

construction of any obstruction on the 

waters of the United States not authorized 

by congress or approved by the USACE

Clean Water Act 33 USC § 1342 requires 

a permit from the USACE prior to any 

discharge of dredged or fill material 

into navigable waters (waters of the US 

[including streams])

Executive Order 11988 requires federal 

agencies to avoid adverse impacts to 

floodplains. (see also D.O. 77-2

Executive Order 11990 requires plans for 

potentially affected wetlands (including 

riparian wetlands). (see also D.O. 77

None applicable

Section 4.1 requires NPS to manage 

natural resources to preserve fundamental 

physical and biological processes, as well 

as individual species, features, and plant 

and animal communities; maintain all 

components and processes of naturally 

evolving park ecosystems

Section 4.1.5 directs the NPS to reestablish natural functions and processes 

in human-disturbed components of natural 

systems in parks, unless directed otherwise 

by Congress

Section 4.4.2.4 directs the NPS to allow 

natural recovery of landscapes disturbed by 

natural phenomena, unless manipulation of 

the landscape is necessary to protect park 

development or human safety.

Section 4.6.4 directs the NPS to

(1) manage for the preservation of 

floodplain values; [and] (2) minimize 

potentially hazardous conditions associated 

with flooding

Section 4.6.6 directs the NPS to manage 

watersheds as complete hydrologic systems 

and minimize human-caused disturbance 

to the natural upland processes that deliver 

water, sediment, and woody debris to 

streams

Section 4.8.1 directs the NPS to allow 

natural geologic processes to proceed 

unimpeded. Geologic processes...include

erosion and sedimentation...processes.

Section 4.8.2 directs the NPS to protect 

geologic features from the unacceptable 

impacts of human activity while allowing 

natural processes to continue
123

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Soils

Soil and Water Resources Conservation 

Act, 16 USC §§ 2011–2009 provides for 

the collection and analysis of soil and 

related resource data and the appraisal of 

the status, condition, and trends for these 

resources

Farmland Protection Policy Act, 7 USC 

§ 4201 et. seq. requires NPS to identify

and take into account the adverse effects 

of Federal programs on the preservation 

of farmland; consider alternative actions, 

and assure that such Federal programs 

are compatible with State, unit of local 

government, and private programs 

and policies to protect farmland. NPS

actions are subject to the FPPA if they 

may irreversibly convert farmland (directly 

or indirectly) to nonagricultural use and 

are completed by a Federal agency or 

with assistance from a Federal agency.

Applicable projects require coordination 

with the Department of Agriculture’s 

Natural Resources Conservation Service 

(NRCS)

7 CFR Parts 610 and 611 are the US 

Department of Agriculture regulations 

for the Natural Resources Conservation 

Service. Part 610 governs the NRCS

technical assistance program, soil erosion 

predictions, and the conservation of private 

grazing land. Part 611 governs soil surveys

and cartographic operations. The NRCS

works with the NPS through cooperative 

arrangements

Section 4.8.2.4 requires NPS to

-prevent unnatural erosion, removal, and 

contamination;

-conduct soil surveys;

-minimize unavoidable excavation; and

-develop/follow written prescriptions 

(instructions)

Mining Claims

Mining in the Parks Act of 1976, 54 

USC § 100731 et seq. authorizes NPS 

to regulate all activities resulting from 

exercise of mineral rights, on patented and 

unpatented mining claims in all areas of the 

System, in order to preserve and manage 

those areas

General Mining Law of 1872, 30 USC 

§ 21 et seq. allows US citizens to locate 

mining claims on Federal lands. Imposes

administrative and economic validity 

requirements for “unpatented” claims (the 

right to extract Federally-owned locatable 

minerals). Imposes additional requirements

for the processing of “patenting” claims 

(claimant owns surface and subsurface)

Use of patented mining claims may be 

limited in Wild and Scenic Rivers

Surface Uses Resources Act of 1955, 

30 USC § 612 restricts surface use of 

unpatented mining claims to mineral 

activities

36 CFR § 5.14 prohibits prospecting, 

mining, and the location of mining claims 

under the general mining laws in park 

areas except as authorized by law

36 CFR Part 6 regulates solid waste 

disposal sites in park units

36 CFR Part 9, Subpart A requires the 

owners/operators of mining claims to 

demonstrate bona fide title to mining 

claim; submit a plan of operations to NPS 

describing where, when, and how; prepare/

submit a reclamation plan; and submit a 

bond to cover reclamation and potential 

liability

Section 6.4.9 requires NPS to seek to 

remove or extinguish valid mining claims in 

wilderness through authorized processes, 

including purchasing valid rights. Where

rights are left outstanding, NPS policy is 

to manage mineral-related activities in 

NPS wilderness in accordance with the 

regulations at 36 CFR Parts 6 and 9A

Section 8.7.1 prohibits location of new 

mining claims in parks; requires validity 

examination prior to operations on 

unpatented claims; and confines operations 

to claim boundaries
124

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Nonfederal Oil and Gas

NPS Organic Act, 54 USC § 100751 et 

seq. authorizes the NPS to promulgate 

regulations to protect park resources and 

values (from, for example, the exercise of 

mining and mineral rights)

Individual Park Enabling Statutes:

16 USC § 230a (Jean Lafitte NHP & Pres.

16 USC § 450kk (Fort Union NM)

16 USC § 459d-3 (Padre Island NS)

16 USC § 459h-3 (Gulf Islands NS)

16 USC § 460ee (Big South Fork NRRA)

16 USC § 460cc-2(i) (Gateway NRA)

16 USC § 460m (Ozark NSR)

16 USC § 698c (Big Thicket N Pres.

16 USC § 698f (Big Cypress N Pres.

36 CFR Part 6 regulates solid waste 

disposal sites in park units

36 CFR Part 9, Subpart B requires the 

owners/operators of nonfederally owned 

oil and gas rights to

-demonstrate bona fide title to mineral 

rights;

-submit a plan of operations to NPS 

describing where, when, how they intend 

to conduct operation

-prepare/submit a reclamation plan; and

-submit a bond to cover reclamation and 

potential liability

43 CFR Part 36 governs access to 

nonfederal oil and gas rights located in, or 

adjacent to, National Park System units in 

Alaska

Section 8.7.3 requires operators to comply 

with 9B regulations

Nonfederal minerals other than oil and gas

NPS Organic Act, 54 USC §§ 100101 and 

100751

Surface Mining Control and 

Reclamation Act of 1977, 30 USC § 

1201 et. seq. prohibits surface coal 

mining operations on any lands within the 

boundaries of a NPS unit, subject to valid 

existing rights

NPS regulations at 36 CFR Parts 1, 5, 

and 6 require the owners/operators of 

other types of mineral rights to obtain 

a special use permit from the NPS as a 

§ 5.3 business operation, and § 5.7 

Construction of buildings or other facilities, 

and to comply with the solid waste 

regulations at Part 6

SMCRA Regulations at 30 CFR Chapter 

VII govern surface mining operations on 

Federal lands and Indian lands by requiring 

permits, bonding, insurance, reclamation, 

and employee protection. Part 7 of the

regulations states that National Park System 

lands are unsuitable for surface mining

Section 8.7.3 states that operators 

exercising rights in a park unit must comply 

with 36 CFR Parts 1 and 5
125

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Federal Mineral Leasing (Oil and Gas, Salable Minerals, and Non-locatable Minerals)

The Mineral Leasing Act, 30 USC § 181 

et seq., and the Mineral Leasing Act for 

Acquired Lands, 30 USC § 351 et seq. 

do not authorize the BLM to lease federally 

owned minerals in NPS units

Exceptions: Glen Canyon NRA (16 USC § 

460dd et seq.), Lake Mead NRA (16 USC 

§ 460n et seq.), and Whiskeytown-ShastaTrinity NRA (16 USC § 460q et seq.) 

authorizes the BLM to issue federal mineral 

leases in these units provided that the BLM 

obtains NPS consent. Such consent must

be predicated on an NPS finding of no 

significant adverse effect on park resources 

and/or administration

Exceptions: Native American Lands 

Within NPS Boundaries Under the Indian 

Allottee Leasing Act of 1909, (25 USC 

§ 396), and the Indian Leasing Act of 

1938 (25 USC §§ 396a, 398 and 399) 

and Indian Mineral Development Act of 

1982 (25 USC §§ 2101-2108), all minerals 

are subject to lease and apply to Native 

American trust lands within NPS units

Federal Coal Leasing Amendments Act 

of 1975, 30 USC § 201 does not authorize 

the BLM to issue leases for coal mining on 

any area of the national park system

36 CFR § 5.14 states prospecting, mining, 

and...leasing under the mineral leasing 

laws [is] prohibited in park areas except as 

authorized by law

BLM regulations at 43 CFR Parts 3100, 

3400, and 3500 govern Federal mineral 

leasing

Regulations re: Native American Lands 

within NPS Units:

25 CFR Part 211 governs leasing of tribal 

lands for mineral development

25 CFR Part 212 governs leasing of 

allotted lands for mineral development

25 CFR Part 216 governs surface 

exploration, mining, and reclamation of 

lands during mineral development

25 CFR Part 224 governs tribal energy 

resource agreements

25 CFR Part 225 governs mineral 

agreements for the development of Indianowned minerals entered into pursuant to 

the Indian Mineral Development Act of 

1982, Pub. L. No. 97-382, 96 Stat. 1938 

(codified at 25 USC §§ 2101-2108).

30 CFR §§ 1202.100-1202.101 governs 

royalties on oil produced from Indian 

leases

30 CFR §§ 1202.550-1202.558 governs 

royalties on gas production from Indian 

leases

30 CFR §§ 1206.50-1206.62 and §§ 

1206.170-1206.176 governs product 

valuation for mineral resources produced 

from Indian oil and gas leases

30 CFR § 1206.450 governs the valuation 

coal from Indian Tribal and Allotted leases

43 CFR Part 3160 governs onshore oil and 

gas operations, which are overseen by the 

BLM

Section 8.7.2 states that all NPS units 

are closed to new federal mineral leasing 

except Glen Canyon, Lake Mead and 

Whiskeytown-Shasta-Trinity NRAs

Park Use of Sand and Gravel

Materials Act of 1947, 30 USC § 601

does not authorize the NPS to dispose of 

mineral materials outside of park units

None applicable

Section 9.1.3.3 clarifies that only the 

NPS or its agent can extract park-owned 

common variety minerals (e.g., sand an

gravel), and:

-only for park administrative uses;

-after compliance with NEPA and other 

federal, state, and local laws, and a 

finding of non-impairment;

-after finding the use is park’s most 

reasonable alternative based on 

environment and economics;

-parks should use existing pits and create 

new pits only in accordance with parkwide borrow management plan;

-spoil areas must comply with Part 6 

standards; and

-NPS must evaluate use of external 

quarries

Any deviation from this policy requires a 

written waiver from the Secretary, Assistant 

Secretary, or Director
126

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Climate Change

Secretarial Order 3289 (Addressing 

the Impacts of Climate Change on 

America’s Water, Land, and Other Natural 

and Cultural Resources) (2009) requires 

DOI bureaus and offices to incorporate 

climate change impacts into long-range 

planning; and establishes DOI regional 

climate change response centers and 

Landscape Conservation Cooperatives to 

better integrate science and management 

to address climate change and other 

landscape scale issues

Executive Order 13653 (Preparing the 

United States for the Impacts of Climate 

Change) (2013) outlines Federal agency 

responsibilities in the areas of supporting 

climate resilient investment; managing 

lands and waters for climate preparedness 

and resilience; providing information, data 

and tools for climate change preparedness 

and resilience; and planning

Executive Order 13693 (Planning for 

Federal Sustainability in the Next Decade) 

(2015) established to maintain Federal 

leadership in sustainability and greenhouse 

gas emission reductions

President’s Climate Action Plan (2013), 

http://www.whitehouse.gov/sites/defaul

files/image/president27sclimateactionplan

pdf 

None applicable

Section 4.1 requires NPS to investigate 

the possibility to restore natural ecosystem 

functioning that has been disrupted by past 

or ongoing human activities. This would

include climate change, as put forth by 

Beavers et al. (in review

NPS Climate Change Response Strategy

(2010) describes goals and objectives to 

guide NPS actions under four integrated 

components: science, adaptation, 

mitigation, and communication

Policy Memo 12-02 (Applying National 

Park Service Management Policies in the 

Context of Climate Change) (2012) applies 

considerations of climate change to the 

impairment prohibition and to maintaining 

“natural conditions”

Policy Memo 14-02 (Climate Change and 

Stewardship of Cultural Resources) (2014) 

provides guidance and direction regarding 

the stewardship of cultural resources in 

relation to climate change

Policy Memo 15-01 (Climate Change 

and Natural Hazards for Facilities) (2015) 

provides guidance on the design of facilities 

to incorporate impacts of climate change 

adaptation and natural hazards when 

making decisions in national parks

DOI Manual Part 523,

Chapter 1 establishes policy and provides 

guidance for addressing climate change 

impacts upon the Department’s mission, 

programs, operations, and personnel

Revisiting Leopold: Resource 

Stewardship in the National Parks

(2012) will guide US National Park natural 

and cultural resource management into 

a second century of continuous change, 

including climate change

Climate Change Action Plan (2012) 

articulates a set of high-priority no-regrets 

actions the NPS will undertake over the 

next few years

Green Parks Plan (2013) is a long-term 

strategic plan for sustainable management 

of NPS operations
The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and 

other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated 

Island Communities.

NPS 608/133731, August 2016
Natural Resource Stewardship and Science 

1201 Oak Ridge Drive, Suite 150 

Fort Collins, Colorado 80525

www.nature.nps.

National Park Service

U.S. Department of the Interior

EXPERIENCE YOUR AMERICATM
This map was produced by James Winter and Georgia Hybels 

(Colorado State University) in August 2016. It is an overview 

of compiled geologic data prepared as part of the NPS 

Geologic Resources Inventory. This map is not a substitute 

for site-specific investigations. 

The GRI team used a compiled map (Willis and Ehler in 

prep.) as the primary source map. That compiled map 

incorporated geologic information from maps published by 

the Utah Geological Survey, US Geological Survey, and 

Canyonlands Natural History Association.

As per source map scale and U.S. National Map Accuracy 

Standards, geologic features represented here are expected 

to be within 50 m (166 ft) of their true location.

All digital geologic data and publications prepared as part of 

the Geologic Resources Inventory are available at the NPS 

Integrated Resource Management Applications Portal 

(IRMA): https://irma.nps.gov/App/Reference/Search. Enter 

“GRI” as the search text and select a park from the unit list.


Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 1 of 14

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area 

Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER

CRETACEOUS to 

EOCENE (101–34

mya) 

Breccia

(TKb) 

Intensely brecciated Navajo Sandstone (Jn).

Mapped on sheets 2 and 3 (in pocket).

None reported. None reported.

Cretaceous–Paleogene Periods: The Laramide 

Orogeny. Folding of the Echo Cliffs monocline during the 

Laramide Orogeny brecciated the Navajo Sandstone and

produced TKb. 

UPPER

CRETACEOUS 

(101–66.0 mya) 

Wahweap 

Formation, 

Lower Member

(Kwl) 

Yellow-gray and yellow-brown mudstone with variable 

amounts of trough cross-bedded sandstone, siltstone, 

and minor carbonaceous shale. Thickness: 76–270 m 

(250–900 ft). 

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes with local ledges.

Geologic Type Sections. No official designated type 

section, but probably named for exposures along 

Wahweap Creek.

None reported.

Cretaceous–Paleogene Periods: The Laramide 

Orogeny. The Laramide Orogeny eliminated the Western 

Interior Seaway and deformed strata on the Colorado 

Plateau. As sea level fell, Kwl was deposited in the 

recreation area.

UPPER 

CRETACEOUS 

(101–66.0 mya)

Straight Cliffs 

Formation, Drip 

Tank Member

(Ksd) 

Yellow-gray and yellow-brown, fine- to mediumgrained, lenticular sandstone. Minor mudstone and 

pebble conglomerate. Commonly iron stained and 

contains iron oxide concretions. Present in westernmost 

part of the map area. Thickness: 43–170 m (140–550 

ft). 

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms cliffs and benches.

Paleontological Resources. Turtle and crocodilian 

fragments in Grand Staircase-Escalante National 

Monument.

None reported.

Cretaceous–Paleogene Periods: The Laramide 

Orogeny. The Laramide Orogeny eliminated the Western 

Interior Seaway and deformed strata on the Colorado 

Plateau. As sea level fell, the shoreface, beach, lagoon, 

and marsh environments of Ks were deposited in the 

recreation area.

UPPER 

CRETACEOUS

(101–66.0 mya)

Straight Cliffs 

Formation, John 

Henry Member

(Ksj) 

Yellow-gray sandstone, gray mudstone, carbonaceous 

mudstone, shale, and coal. Coal-barren zones are 

dominated by thick-bedded to massive cliff-forming 

sandstones. The lower approximately 200 m (600 ft) are

preserved in the recreation area.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes and ledges. 

Sandstone forms cliffs.

Sedimentary Rocks and Sedimentary Rock 

Features. Nearshore marine mudstone and coal from 

coastal marshes.

Paleontological Resources. Fossils are found in Grand 

Staircase-Escalante National Monument but not in the 

recreation area.

Economic Minerals. Contains the major coal resources 

of the Kaiparowits Plateau. Coal beds are locally 6 m 

(20 ft) or more thick.

Slope Movement Hazards and Risk. Erosion of the 

underlying Kt results in cliff collapse and rockfalls.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from Ksj have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Abandoned Mineral Lands and Potential Mining 

Activity. Ksj contains the major coal resources on the 

Kaiparowits Plateau. Coal seams may spontaneously 

combust.

Cretaceous–Paleogene Periods: The Laramide 

Orogeny. The Laramide Orogeny eliminated the Western 

Interior Seaway and deformed strata on the Colorado 

Plateau. As sea level fell, the shoreface, beach, lagoon, 

and marsh environments of Ks were deposited in the 

recreation area.

UPPER 

CRETACEOUS 

(101–66.0 mya)

Straight Cliffs 

Formation, 

Lower (Smoky 

Hollow and 

Tibbet Canyon) 

Members

(Ksl) 

Smoky Hollow Member: white and gray, fine- to 

medium-grained sandstone, mudstone, carbonaceous 

mudstone, and coal. Thickness: 7–71 m (24–234 ft). 

Tibbet Canyon Member: yellow-gray to brown 

sandstone with thin layers of gray mudstone and 

siltstone. Gradational with Tropic Shale. Thickness: 21–

56 m (70–185 ft). 

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Smoky Hollow Member: ledgeand slope-forming beds. Tibbet Canyon Member: forms 

cliffs.

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedding. Smoky Hollow features 

represent fluvial, floodplain, lagoon, and marsh 

settings. Tibbet Canyon features represent beach and 

shallow marine environments.

Paleontological Resources. Abundant in Grand 

Staircase-Escalante National Monument. Coal is in Glen 

Canyon National Recreation Area.

Slope Movement Hazards and Risk. Erosion of the 

underlying Kt results in cliff collapse and rockfalls.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from Ksl have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present. 

Cretaceous–Paleogene Periods: The Laramide 

Orogeny. The Laramide Orogeny eliminated the Western 

Interior Seaway and deformed strata on the Colorado 

Plateau. As sea level fell, the shoreface, beach, lagoon, 

and marsh environments of Ks were deposited in the 

recreation area.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 2 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER 

CRETACEOUS

(101–66.0 mya)

Tropic Shale

(Kt)

Gray, fossiliferous marine mudstone and shale with 

some gray sandstone, bentonitic claystone, siltstone, 

and limestone beds. Approximately equivalent to 

Tununk Shale (Kmt) but Tropic name is used south of 

Kaiparowits Plateau. Thickness: 150–230 m (500–750 

ft).

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes, badlands 

topography and landslide scarps.

Sedimentary Rocks and Sedimentary Rock 

Features. Mudstone and marine fossils.

Paleontological Resources. Ammonites, bivalves, 

sharks, rays, turtles, and plesiosaurs.

Slope Movement Hazards and Risk. The bentonite in 

Kt makes the unit susceptible to slope movements.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Cretaceous Period: Western Interior Seaway. In the 

Late Cretaceous, subsidence of the western interior caused 

by the Sevier Orogeny allowed incursions of the sea from 

both the north and south. Eventually, the Western Interior 

Seaway formed, bisecting North America and connecting 

the Gulf of Mexico with the Arctic Ocean. Kt accumulated 

within this seaway.

UPPER 

CRETACEOUS

(101–66.0 mya)

Mancos Shale, 

Ferron 

Sandstone 

Member

(Kmf)

Gray to yellowish-brown, fine- to very fine grained 

sandstone with thin beds of siltstone and coaly shale. 

Present only northwest of Bullfrog. Thickness: 60–87 m 

(200–285 ft).

Mapped on sheet 2 (in pocket).

Landscape Features. Forms a thin resistant cap on 

small mesas and benches

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedding.

None reported.

Cretaceous Period: Western Interior Seaway. In the 

Late Cretaceous, subsidence of the western interior caused 

by the Sevier Orogeny allowed incursions of the sea from 

both the north and south. Eventually, the Western Interior 

Seaway formed, bisecting North America and connecting 

the Gulf of Mexico with the Arctic Ocean. Kmf was 

deposited along the fluctuating coastline of this seaway.

UPPER 

CRETACEOUS

(101–66.0 mya)

Mancos Shale, 

Tununk Shale 

Member

(Kmt)

Dark gray, laminated to very thin bedded shale and silty 

shale. Weathers to pale gray to pale yellowish gray. 

Poorly exposed. Approximately equivalent to Kt. Present 

only northwest of Bullfrog. Thickness: 170–200 m (550–

650 ft).

Mapped on sheet 2 (in pocket).

Landscape Features. Forms slope or broad low 

badlands topography. None reported.

Cretaceous Period: Western Interior Seaway. In the 

Late Cretaceous, subsidence of the western interior caused 

by the Sevier Orogeny allowed incursions of the sea from 

both the north and south. Eventually, the Western Interior 

Seaway formed, bisecting North America and connecting 

the Gulf of Mexico with the Arctic Ocean. Kmt

accumulated within this seaway.

UPPER 

CRETACEOUS

(101–66.0 mya)

Dakota 

Formation

(Kd)

Light-brown sandstone, sandy and carbonaceous 

mudstone, shaley sandstone, conglomerate, dark-brown 

to black carbonaceous shale and coal. Discontinuous 

local basal conglomerate in the lower part fills 

paleotopographic lows. Deposited unconformably above

“Jm” units, Jr, and Je. Thickness: highly variable, but 

generally thickens westward from 1–46 meters (3–150 

ft). The lower part of Kd may be partly Early Cretaceous 

in age, which would make it equivalent to the Cedar 

Mountain Formation in central Utah.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Middle part forms ledges and 

slopes. 

Sedimentary Rocks and Sedimentary Rock 

Features. Marine fossils in the upper part. Coal in the 

middle part. Conglomerate and fluvial channels in lower 

part.

Paleontological Resources. Dinosaur tracks, plant 

fossils, nonmarine fauna, marine invertebrate fossils. 

Abundant fossils in the Grand Staircase-Escalante 

National Monument.

Unconformities. K-0 unconformity at the base of Kd.

Folds and Faults. Exposed on the crest of the Smoky 

Mountain anticline.

Laccoliths. Forms the dome of Navajo Mountain.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Coal Mining: thin, discontinuous coal seams.

Burning Coal Beds: potential for coal seams to 

spontaneously combust.

Cretaceous Period: Western Interior Seaway. In the 

Late Cretaceous, subsidence of the western interior caused 

by the Sevier Orogeny allowed incursions of the sea from 

both the north and south. Eventually, the Western Interior 

Seaway formed, bisecting North America and connecting 

the Gulf of Mexico with the Arctic Ocean. Kd was 

deposited along the fluctuating coastline of this seaway.

Rocks from the Early Cretaceous Epoch (145–101 million years ago) are not mapped within Glen Canyon National Recreation Area.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 3 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER JURASSIC 

(164–145 mya) 

Morrison 

Formation,

Brushy Basin 

Member

(Jmb) 

Dark-brown to purplish-red, smectitic mudstone. Minor 

sandstone and conglomerate with gray quartzite and 

chert clasts. Mapped in the Bullfrog Creek area 

northwest of Bullfrog Bay. Cut out by a major 

unconformity near Fiftymile Mountain and in the 

southwest part of the map area where Kd overlies Jms. 

Thickness: about 60 m (200 ft).

Mapped on sheet 2 (in pocket).

Landscape Features. Forms mostly bare slopes.

Economic Minerals. Morrison Formation contains 

uranium.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. A major 

transgression of the inland seaway from the north destroys 

the vast ergs that once covered the Colorado Plateau. Jr

was deposited in shallow marine, tidal flat, and eolian

environments. When sea level fell, the Morrison Formation

was deposited across western North America.

UPPER JURASSIC 

(164–145 mya)) 

Morrison 

Formation,

Salt Wash 

Member

(Jms) 

Gray, weathering to dark brown, very fine to mediumgrained, pebble conglomerate, and conglomeratic 

sandstone interbedded with minor purple, green, and 

reddish-brown mudstone and siltstone. A resistant basal 

ledge commonly protrudes as an overhanging lip above 

the ledgy Je beds below. Regional thickness ranges from 

0 to 94 m (0–310 ft). Cut out by an unconformity in the 

southwestern corner of the recreation area.. 

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms ledgy cliffs and mesas and 

Alcove Arch in Rock Creek Bay. 

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedded sandstone.

Paleontological Resources. Sauropod tracks in the 

Lost Spring Wash area.

Folds and Faults. Forms the crest of Mule Creek 

anticline.

Economic Minerals. Morrison Formation contains 

uranium.

Landscape Safety Hazards. Documented fall from Jms

outcrop.

Slope Movement Hazards and Risk. Rockfall hazard.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Uranium Mining: potential hazard. Uranium 

occurs in sandstones and conglomerates.

Jurassic Period: Extensive Dune Fields. A major 

transgression of the inland seaway from the north destroys 

the vast ergs that once covered the Colorado Plateau. Jr

was deposited in shallow marine, tidal flat, and eolian

environments. When sea level fell, the Morrison Formation 

was deposited across western North America.

UPPER JURASSIC

(164–145 mya)) 

Morrison 

Formation, 

Tidwell Member 

and/or 

Summerville 

Formation 

(Jsmt) 

Interbedded, gray to brown, very fine to fine-grained 

sandstone, siltstone, mudstone, and shale. Thickness: 

10–26 m (35–85 ft). Along the base of Fiftymile 

Mountain, the unit has been considered to be either the 

Summerville Formation or the Tidwell Member of the 

Morrison Formation.

Mapped on sheet 2 (in pocket).

Landscape Features. Forms ledgy cliffs to steep ledgy 

slopes.

Paleontological Resources. Sauropod tracks with skin 

impressions. Bone fragments. Termite nests. Pterosaur 

(Pteraichnus).

Slope Movement Hazards and Risk. Rockfall hazard.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. A major 

transgression of the inland seaway from the north destroys 

the vast ergs that once covered the Colorado Plateau. Jr

was deposited in shallow marine, tidal flat, and eolian 

environments. When sea level fell, the Morrison Formation 

was deposited across western North America.

UPPER JURASSIC

(164–145 mya)

San Rafael 

Group

Romana 

Sandstone

(Jr) 

Yellow, brown, and gray, very fine- to fine-grained, 

calcareous sandstone with thin beds of reddish-brown 

sandy siltstone. Mapped in the southwest part of map 

area. Thickness: 0–45 m (0–145 ft).

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms massive to ledgy cliffs. 

Romana Mesa.

Sedimentary Rocks and Sedimentary Rock 

Features. Planar beds of calcareous sandy siltstone and 

gypsum are characteristic of nearshore, tidal flat, and 

shallow marine depositional environments. Local highangle cross-bedding (sand dunes).

Unconformities. Bounded by the J-3 and J-5 regional 

unconformities.

Geologic Type Sections. Romana Mesa north of 

Wahweap Bay.

Slope Movement Hazards and Risk. Rockfall hazard.

Jurassic Period: Extensive Dune Fields. A major 

transgression of the inland seaway from the north destroys 

the vast ergs that once covered the Colorado Plateau. Jr

was deposited in shallow marine, tidal flat, and eolian 

environments.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 4 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Entrada 

Sandstone

(Je) 

Generally consists of upper, middle, and lower (informal) 

members that are not mapped separately. The 24–122 

m (80–400 ft) thick upper member (Escalante Member) 

has been cut out by the J-3 unconformity throughout 

most of the map area. Unconformable upper contact. 

Total thickness of Je: 90–300 m (300–1000 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Cliffs, slickrock, arches, natural 

bridges, hoodoos, sandstone pipes, weathering pits. 

Escalante Member: forms cliffs. Cannonville Member: 

forms slopes. Gunsight Butte Member: forms cliffs.

Sedimentary Rocks and Sedimentary Rock 

Features. High-angle cross-beds (eolian dunes).

Unusual Sedimentary Rock Features. Tafoni and 

contorted bedding.

Paleontological Resources. Theropod and sauropod 

tracks, root traces, insect burrows, vertebrate burrows, 

and sand-swimming traces.

Unconformities. J-3 unconformity

Slope Movement Hazards and Risk. Rockfall hazard.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north, yet Je became the most 

widespread of the preserved ergs on the Colorado Plateau.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Entrada 

Sandstone, 

middle member

(Jem)

Orange to brown, medium- to thick-bedded, crossbedded, calcareous, very fine grained sandstone with 

thin partings of siltstone, mudstone, and scarce very thin 

beds of bentonitic clay. Thickness: about 110 m (360 ft). 

Formal name is the Cannonville Member.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Generally forms red and white 

banded ledgy cliffs. Refer to Je for potential management issues.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north, yet Je became the most 

widespread of the preserved ergs on the Colorado Plateau.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Entrada 

Sandstone, 

lower member

(Jel) 

Yellow to orange, thick-bedded to massive, calcareous, 

fine-grained sandstone with thin partings of siltstone 

and mudstone. Thickness: about 140 m (460 ft). Formal 

name is the Gunsight Butte Member.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms massive smooth cliffs, 

rounded bare domes, and broad rolling slickrock swells 

with common large weathering pits. 

Unusual Sedimentary Rock Features. Contorted 

bedding, small internal faults, and complex small-scale 

folds indicate extensive and complex soft-sediment 

deformation.

Refer to Je for potential management issues.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north, yet Je became the most 

widespread of the preserved ergs on the Colorado Plateau.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Carmel 

Formation, 

upper (Winsor 

and Paria River) 

members

(Jcu) 

Winsor Member: reddish-brown, silty sandstone and 

siltstone with locally gypsiferous sandstone. Overlies the 

Paria River Member.

Paria River Member: reddish-brown to gray siltstone and 

silty sandstone capped by pale-gray to pink, silty to 

sandy limestone. 

Jcu thickness: 30–50 m (90–150 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Hoodoos. Forms slopes.

Paleontological Resources. Terrestrial trace fossils are 

found in the upper part of the Carmel Formation 

outside of the recreation area.

Sedimentary Rocks and Sedimentary Rock 

Features. Features, such as gypsum and silty limestone, 

that characterize nearshore, tidal flat, or shallow marine 

depositional environments. Commonly contorted and 

deformed together with the lower part of the Entrada 

Formation.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from “Jc” units have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Carmel 

Formation, 

Winsor Member

(Jcw)

Reddish-brown, silty sandstone and siltstone with locally 

gypsiferous sandstone. Mapped separate from Jcu in the 

southwest part of the map area. Thickness: 40–46 

meters (130–150 ft). Thins to the east.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes.

Paleontological Resources. Terrestrial trace fossils are 

found in the upper part of the Carmel Formation 

outside of the recreation area.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from “Jc” units have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 5 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Carmel 

Formation, Paria 

River Member

(Jcp)

Reddish-brown to gray siltstone and silty sandstone 

capped by pale-gray to pink, silty to sandy limestone. 

Mapped separate from Jcu in the southwest part of the 

map area. Thickness: 15–21 m (50–70 ft). Thins to the 

east.

Mapped on sheet 2.

Paleontological Resources. Terrestrial trace fossils are 

found in the upper part of the Carmel Formation 

outside of the recreation area.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from “Jc” units have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Carmel 

Formation, Judd 

Hollow Tongue 

and Page 

Sandstone, 

undivided

(Jpj) 

Judd Hollow Tongue: reddish-brown siltstone and 

grayish-orange, thin-bedded, fine-grained sandstone. 

Thickness: 0–90 m (0–300 ft); 18–30 m (60–100 ft) in 

the Hite area.

Page Sandstone (see note below): yellow to gray, thickto massive-bedded, fine- to medium-grained sandstone. 

In some areas, divided into two tongues by the Judd 

Hollow Tongue.

Note: Recent research recommended restricting the 

Page Sandstone to areas (mostly Arizona) where the 

Judd Hollow Member cannot be identified. Many of the 

mapped areas of “Page Sandstone” in the GRI GIS data 

should be considered Temple Cap Formation (see 

“Unconformities” section of report and Doelling et al. 

2013).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Page Sandstone (see note): forms 

ledges and cliffs. Judd Hollow Tongue: forms slopes,

Sedimentary Rocks and Sedimentary Rock 

Features. Page Sandstone: large-scale, high-angle 

cross-bedding typical of eolian sand dunes. Quartz 

grains are very well sorted, well rounded, and frosted 

from wind abrasion.

Unusual Sedimentary Rock Features. Page 

Sandstone: tafoni.

Paleontological Resources. Petrified wood.

Unconformities. J-1 unconformity marks the base of 

the Page Sandstone.

Geologic Type Sections. Just south of the recreation 

area on Manson Mesa.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Page Sandstone, 

Thousand 

Pockets Tongue

(Jpt) 

Gray to brown, thick-bedded, cross-bedded sandstone 

with thin, red siltstone partings. Forms ledges that 

overlie the slopes of Jcj. Thickness: 27–60 m (90–200 ft).

Note: Recent research has redefined the Thousand 

Pockets Tongue as a member of the Carmel Formation

(Doelling et al. 2013). 

Mapped on sheets 2 and 3 (in pocket).

Sedimentary Rocks and Sedimentary Rock 

Features. Large-scale, high-angle cross-bedding typical 

of eolian sand dunes. Quartz grains are very well sorted, 

well rounded, and frosted from wind abrasion.

None reported.

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.

MIDDLE JURASSIC

(174–164 mya)

San Rafael 

Group

Carmel 

Formation, Judd 

Hollow Tongue

(Jcj)

Reddish-brown sandstone, siltstone, and minor red and 

lavender limestone. Mapped separately only near the 

southwestern side of map area. Thickness: 0–70 meters 

(0–230 ft). Pinches out eastward.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms a prominent slope 

between Page Sandstone tongues northeast of Fiftymile 

Mountain and in the Bullfrog and Hite areas, where it is 

mapped as Jpj.

None reported. 

Jurassic Period: Extensive Dune Fields. A sea 

encroached into west-central Utah from the north, and 

coastal eolian, sabkha, tidal flat, ephemeral stream, and 

restricted marine environments developed in the 

recreation area. The encroaching sea eliminated the sand 

source from the north.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 6 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

LOWER JURASSIC

(201–174 mya)

Glen Canyon 

Group

Navajo 

Sandstone

(Jn) 

Yellowish-gray, reddish-brown, and reddish-orange, 

massive, cross-bedded sandstone. Contains thin lenses 

of gray sandy limestone, dolomite, and calcareous 

siltstone as much as 15 m (50 ft) thick and 3–5 km (2–3 

mi) long with common algae laminae, ripple marks, and 

mudcracks (Jnl). Gradational lower contact with Jk. 

Thickness ranges from about 170 m to 340 m (550–

1100 ft) with a maximum of about 340 m (1100 ft) 

exposed in Glen Canyon below the dam.

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms rounded cliffs, knobs, 

buttes, mesa rims, slickrock, slot canyons, alcoves, 

hanging gardens, arches, natural bridges. Entrenched 

meanders have cut through Jn, and the cross-beds in Jn

are often highlighted by desert varnish.

Sedimentary Rocks and Sedimentary Rock 

Features. High-angle cross-bedding, well sorted, 

rounded, and frosted quartz grains typical of eolian 

sand dunes. Cross-bed sets range up to 20 meters (60 

ft) thick. 

Unusual Sedimentary Rock Features. Moqui (Moki) 

marbles, contorted bedding from soft-sediment 

deformation, and tafoni. Features representing oases in 

the dune field include oscillation ripples, limestone 

beds, algal layers, and dinosaur tracks.

Paleontological Resources. Dinosaur tracks include 

Eubrontes, Anchisauripus, Otozoum, Batrachopus, 

Brasilichnium, and Grallator. Distinctive unionid clam 

bed. Petrified trees. Cenozoic fossils collected from 

Bechan Cave, an alcove formed in Jn.

Unconformities. J-1 unconformity separates Jn from 

overlying strata.

Folds and Faults. Jn forms most of the crest of the 

Circle Cliffs anticline.

Joints. Prominent, parallel to conjugate near-vertical 

joints.

Landscape Safety Hazards. Documented fall from Jn

cliff at Horseshoe Bend Overlook.

Slope Movement Hazards and Risk. Rockfall hazard.

Flash Floods and Debris Flows. Hazard in slot canyons 

carved in Jn.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Navajo Sandstone and Potential Glen Canyon Dam 

Failure. Failure of the porous Jn at dam spillways could 

lead to catastrophic consequences for downstream 

communities and others who rely on Lake Powell water.

Potential Impacts from Global Climate Change. 

Decreases in precipitation may adversely affect water 

availability for the aquifers, springs, and seeps, as well as 

impact the fragile ecosystems of hanging gardens.

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. Extensive sand 

deserts (ergs) gradually inundated the fluvial systems of Jk, 

resulting in one of the largest dune fields ever recorded in 

the history of Earth. The main part of Jn was deposited in 

a large erg with local interdunal playas (oasis-like setting). 

The basal part of Jn represents deposition in a sabkha 

environment that had abundant wind-blown sand.

LOWER JURASSIC

(201–174 mya)

Glen Canyon 

Group

Limestone and 

dolomite beds in 

Navajo 

Sandstone

(Jnl) 

Gray, thin-bedded limestone, dolomite, and calcareous 

siltstone. Thin lenses of Jnl are up to about 5 km (3 mi) 

long. As many as 10 lenses are present in the walls of 

Navajo Canyon, but 0–3 lenses are more typical.

Mapped on sheets 1, 2, and 3 (in pocket).

Sedimentary Rocks and Sedimentary Rock 

Features. Locally contain shallow channels with coarse, 

angular ripup clasts, algal structures, and dinosaur 

tracks.

None reported.

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. Extensive sand 

deserts (ergs) gradually inundated the fluvial systems of Jk, 

resulting in the largest dune fields ever recorded in the 

history of Earth. Glen Canyon National Recreation Area 

contains the largest number of Jnl lenses known 

anywhere within the Navajo Sandstone. Jnl represent 

shallow playas or lakes that formed in interdunal areas of 

the Jn erg and provide evidence that Jn was deposited in 

an area with a high water table.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 7 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

LOWER JURASSIC

(201–174 mya)

Glen Canyon 

Group

Kayenta 

Formation 

(Jk) 

Brown, reddish-orange, and purplish-red, lenticular, 

medium- to thick-bedded, locally cross-bedded, fine- to 

medium-grained sandstone, silty sandstone, and 

mudstone. A few thin lenses of conglomerate and 

limestone. Jk is divided into a lower Springdale 

Sandstone Member (Jks) and an informal upper member 

that contains more siltstone than sandstone. Jks is 

exposed only in the Lees Ferry area Thickness: 58–104 

meters (190–340 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms alternating cliffs, buttes, 

slot canyons, and steep ledgy slopes. Hanging gardens 

at contact with Jn. Entrenched meanders have cut 

through Jk.

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedded sandstone and silt represent 

braided and meandering streams.

Paleontological Resources. Dinosaur tracks include 

Eubrontes and Grallator. Vertebrate, invertebrate, trace, 

and plant fossils have been found in many other 

locations on the Colorado Plateau.

Folds and Faults. Jk forms the steep slope of the 

Waterpocket Fold.

Joints. Large joint sets.

Slope Movement Hazards and Risk. Rockfall hazard.

Flash Floods and Debris Flows. Hazard in slot canyons 

carved in Jk.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Abandoned material (cables, bricks, glass) from 

an oil and gas well. No natural resource impact. Major tar 

sands exploration site that was restored in the 1990s.

Potential Impacts from Global Climate Change. 

Decreases in precipitation may adversely affect water 

availability for the aquifers, springs, and seeps, as well as 

impact the fragile ecosystems of hanging gardens.

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. Jk represents 

rivers that meandered through and eventually overran the 

JTRw dunes. 

LOWER JURASSIC

(201–174 mya)

Glen Canyon 

Group

Kayenta 

Formation, 

Springdale 

Sandstone 

Member

(Jks)

Reddish-brown, fine-grained, cross-bedded sandstone 

and minor siltstone and mudstone. Only recognized in 

the Lees Ferry area where it is 55–68 m (180–223 ft) 

thick. 

Mapped on sheets 2 and 3 (in pocket).

Sedimentary Rocks and Sedimentary Rock 

Features. Horizontal and trough cross-bedding.

Paleontological Resources. Semionotid (ray-finned) 

fish and dinosaur tracks.

Slope Movement Hazards and Risk. Rockfall hazard.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. Jks represents a 

major fluvial system at the base of Jk. 

UPPER TRIASSIC 

to LOWER 

JURASSIC (237–

174 mya)

Glen Canyon 

Group

Wingate 

Sandstone

(JTRw) 

Reddish-orange to reddish-brown, massive, crossbedded, very fine to fine-grained eolian sandstone. 

Grains are mostly subangular to subrounded, wellsorted, and frosted. Upper contact varies from sharp to 

very gradational and is placed at top of highest massive 

eolian sandstone and below ledgy beds. Thickness: 60–

104 meters (200–340 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Massive, vertical to rounded cliffs 

commonly streaked by desert varnish. Entrenched 

meanders have cut through JTRw. Landscape scarps.

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedding typical of eolian processes.

Unusual Sedimentary Rock Features. Tafoni.

Paleontological Resources. Dinosaur tracks. 

Redondasaurus skull discovered just outside the 

recreation area.

Unconformities. Deposited above the TR-5 

unconformity, which was called the J-0 unconformity 

until new research showed that the lower part of the 

Wingate and equivalent strata are Upper Triassic in age.

Joints. Strongly cut by near-vertical joints.

Unconsolidated Surficial Deposits. Slump blocks.

Slope Movement Hazards and Risk. Erosion of the 

underlying Chinle Formation results in cliff collapse, 

rockfalls, and slides.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. Sand transported 

from as far north as Montana and Alberta became the 

dunes preserved in JTRw. 
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 8 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER TRIASSIC 

to LOWER

JURASSIC 

(237–174 mya)

Glen Canyon 

Group

Moenave 

Formation, 

Dinosaur 

Canyon Member

(JTRmd) 

Thick to massive, eolian (Wingate-like) sandstone near 

the base grades upward into thin- to thick-bedded, 

reddish-orange to reddish-brown, fine-grained 

sandstone and siltstone. Some beds near the base are 

equivalent to TRcc. In the recreation area, JTRmd is only 

recognized in the Lees Ferry area. Thickness; about 90–

134 m (290–440 ft).

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms thin to thick ledgy cliffs 

and steep slopes.

Sedimentary Rocks and Sedimentary Rock 

Features. Lithologic features suggest deposition by 

fluvial processes.

None reported. 

Jurassic Period: Extensive Dune Fields. Jurassic deserts 

began to inundate the Colorado Plateau. JTRmd was 

deposited in a broad coastal plain environment with low 

energy streams and lakes.

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, 

Church Rock 

Member 

(TRcc) 

Reddish-brown, fine- to coarse-grained sandstone and 

siltstone. Some conglomerate beds are locally present 

near the base of the unit. In the Hite area, the upper 

part of TRcc is a thick [6–26 m (20–85 ft)] bed of 

conglomeratic and purplish-red sandstone called the 

Hite bed. Surface often contains JTRw rockfall debris. 

Average thickness: 12–20 m (38–60 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Weathers to alternating steep 

slopes and cliffs. Buttes.

Sedimentary Rocks and Sedimentary Rock 

Features. Fluvial features include ripple laminations, 

mudcracks, and small-scale cross-beds.

Paleontological Resources. Fossil fish bones and 

petrified wood (potentially not in situ). Many additional 

fossils have been found in Grand Staircase-Escalante 

National Monument.

Slope Movement Hazards and Risk. The bentonite in 

the Chinle Formation makes the unit especially susceptible 

to slope movements. 

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest.

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, Owl 

Rock and 

Petrified Forest 

Members

(TRcop) 

Gradational contact between the two members. In most 

areas, it is recognized by a change from strongly colored 

and banded Petrified Forest Member to grayish-purple 

to grayish-yellow ledgy beds with abundant paleosols of 

the overlying Owl Rock. Combined thickness: 85–160 m 

(280–520 ft).

Owl Rock Member: calcareous sandstone, mottled and 

locally brecciated limestone, and siltstone. Commonly 

covered by talus. Thickness: generally 46–76 m (150–

250 ft), but locally thicker [111 m, (365 ft)] at Monitor 

Butte). 

Petrified Forest Member: variegated smectitic claystone 

interbedded with siltstone, sandstone, and pebble 

conglomerate beds. Thickness: 12–160 m (41–520 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Owl Rock Member: forms a 

steep slope with scattered ledges where protected by 

the overlying Wingate; elsewhere forms a low ledgy 

slope. Petrified Forest Member: forms a steep, barren 

“badlands” slope with “popcorn” weathered slopes 

and sandstone and conglomerate ledges. Landslide 

scarps.

Paleontological Resources. Petrified logs. Vertebrate, 

invertebrate, and plant fossils have been discovered at 

locations near the recreation area.

Paleosols. Owl Creek Member: stacked alluvial-plain 

paleosols.

Unconsolidated Surficial Deposits. Slope movement 

deposits (rock slides, landslides, and slumps).

Slope Movement Hazards and Risk. The bentonite in 

the Chinle Formation makes the unit susceptible to slope 

movements, especially where saturated by Lake Powell.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest. The 

Petrified Forest Member was deposited in a fluviallacustrine environment.

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, 

Upper (Church 

Rock, Owl Rock, 

Petrified Forest, 

Moss Back) 

Members

(TRcu)

Members are combined into one unit because contacts 

are not well-defined. Unit thickness: 91–244 m (300–

800 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Overall, TRcu forms a steep to 

ledgy slope commonly covered by talus just below the 

massive JTRw cliff.

See specific members for other features.

Slope Movement Hazards and Risk. The bentonite in 

the Chinle Formation makes the unit especially susceptible 

to slope movements.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 9 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, Moss 

Back Member

(TRcms) 

Brownish-yellow to brown, lenticular, cross-bedded, well 

cemented, fine- to coarse-grained sandstone and thin 

lenses and beds of siltstone and pebble conglomerate. 

TRcms is a discontinuous tongue at the base of the 

Petrified Forest Member in the northern half of the 

recreation area. Thickness: generally 0–15 m (0–50 ft), 

but locally as much as 60 m (200 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Forms cliffs to steeply ledgy 

slopes.

Sedimentary Rocks and Sedimentary Rock 

Features. Fluvial features include cross-bedding and 

rip-up fragments.

Paleontological Resources. Petrified logs. Possible 

dicynodont (large mammal-like reptile) Pentasauropus

tracks.

Unconformities. TR-4 unconformity is at the base of 

TRcms.

Slope Movement Hazards and Risk. The bentonite in 

the Chinle Formation makes the unit especially susceptible 

to slope movements.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest.

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, 

Monitor Butte 

Member

(TRcmn) 

Pale-greenish-gray to reddish-gray to grayish-purple, 

mottled mudstone with many lenticular, cross-stratified 

sandstone and conglomeratic sandstone beds. Contains 

lenses and thin beds of clayey sandstone, limestonepebble conglomerate, rippled gray mica-rich sandstone, 

calcareous shale, and coal. Beds at the top of TRcmn

are locally similar to Petrified Forest strata. Commonly 

smectitic. Differs from Petrified Forest Member by 

having more uniform greenish-gray color and larger 

number of sandstone beds. Thickness: 26–75 meters 

(85–250 ft); 30 m (97 ft) thick at Monitor Butte.

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms small cliffs to steep slopes, 

which generally have soft “popcorn” weathering.

Sedimentary Rocks and Sedimentary Rock 

Features. Fluvial features include cross-bedding and 

rip-up fragments.

Paleontological Resources. Petrified logs, unionids, 

crocodile relative, and coprolites. Significant lacustrine 

fossils from Red Canyon include plants, insects, 

crustaceans, conchostracans, and fish fossils. 

Slope Movement Hazards and Risk. The bentonite in 

the Chinle Formation makes the unit especially susceptible 

to slope movements.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Jomac and other uranium mines. High levels of 

Gamma radiation at the Jomac Mine.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest. 

Although similar to the Petrified Forest Member, TRcmn

was deposited under higher energy conditions.

UPPER TRIASSIC

(237–201 mya)

Chinle 

Formation, 

Shinarump 

Conglomerate 

Member

(TRcs) 

Gray to brown, fine- to coarse-grained sandstone and 

conglomeratic sandstone, with minor lenses of 

mudstone and siltstone. Fills basal fluvial channels that 

cut into the underlying Moenkopi Formation. Thickness: 

generally 0–30 m (0–100 ft), but locally 60 m (200 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms a prominent, 

discontinuous ledgy cliff with thin slope intervals. 

Sedimentary Rocks and Sedimentary Rock 

Features. Conglomerate and sandstone fill paleochannels. These deposits may contain minor uranium 

and copper, and very minor lead, silver, and cobalt.

Paleontological Resources. Fossils of fern stems, 

leaves, and coal. Bone fragments are preserved in 

cobbles. Fossils include tetrapod footprints, swim traces, 

invertebrate shells, insect eggs, and beetle feeding 

traces.

Unconformities. TR-3 unconformity is at the base of 

TRcs.

Economic Minerals. Uranium

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Uranium Mining: potential hazard. Uranium 

occurs in sandstones and conglomerates.

Coal Mining: TRcs is the surface formation at the 

abandoned Spencer coal mine.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Streams cut valleys into the underlying TRm, developing a 

dendritic (tree-like pattern) fluvial system in southeastern 

Utah. The main trunk stream flowed to the northwest.

Because of erosion at the TR-3 unconformity, Middle Triassic rocks (247–237 million years ago) are not recognized and probably not present within Glen Canyon National Recreation Area.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 10 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

LOWER TRIASSIC

(252–247 mya)

Moenkopi 

Formation (main 

part) 

(TRm) 

Reddish-brown, thinly laminated to medium-bedded, 

very fine to fine-grained sandstone and siltstone. 

Distinguished from TRmh by color and grain size. TRmh

is recognized east of Hite and near the San Juan River. 

Divided into TRmu and TRml near Lees Ferry. Thickness: 

53–114 m (175–375 ft), averaging about 90 m (300 ft).

Mapped on sheets 1, 2, and 3 (in pocket). 

Landscape Features. Forms buttes and ledges. 

Contains some arches. Entrenched meanders have cut 

through TRm.

Sedimentary Rocks and Sedimentary Rock 

Features. Common ripple marks and mud cracks 

characteristic of floodplains and low-energy stream 

flow.

Paleontological Resources. Vertebrate tracks, 

swimming claw marks, invertebrate trace fossils, and 

horsetail molds.

Unconformities. TR-3 unconformity separates TRm

from TRc. 

Unconsolidated Surficial Deposits. Slope movement 

deposits (rock slides, landslides, and slumps).

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Tropical climate conditions dominated the region in the 

Early Triassic. The western part of the Colorado Plateau 

consisted of a broad continental shelf while nearshore to 

coastal environments developed in the eastern part of the 

plateau. Sediments spread into Utah from the erosion of 

the Ancestral Rocky Mountains in Colorado. TRm

represents deposition in tidal-flat, sabkha, and low coastalplain environments. 

LOWER TRIASSIC

(252–247 mya)

Moenkopi 

Formation, 

Hoskinnini 

Sandstone 

Member

(TRmh) 

Reddish-brown to grayish-orange, very fine to coarsegrained sandstone. Poorly developed stratification with 

wavy laminations. Unconformably overlies either Pwr or 

Po. Thickness: 0–33 m (0–110 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms knobby cliffs.

Paleontological Resources. Stromatolites.

Unconformities. TR-1 unconformity marks the 

boundary between the Paleozoic Era and deposition of 

TRmh at the beginning of the Mesozoic Era.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Triassic Period: Fluvial Systems in a Tropical Climate. 

Tropical climate conditions dominated the region in the 

Early Triassic. The western part of the Colorado Plateau 

consisted of a broad continental shelf while nearshore to 

coastal environments developed in the eastern part of the 

plateau. Sediments spread into Utah from the erosion of 

the Ancestral Rocky Mountains in Colorado. TRmh was 

deposited in a sabkha environment with sediments filling a 

low area that had been carved into the underlying Po.

LOWER TRIASSIC

(252–247 mya)

Moenkopi 

Formation, 

upper and lower 

members

(TRmu, TRml) 

Upper unit: dark-reddish-brown, even-bedded siltstone 

and sandy siltstone with two to three thin beds of gray 

sandy limestone. Includes a distinctive 5–12-m (15–40 ft) 

thick, massive, pale-brown sandstone at the base. 

Thickness: 0–36 m (0–120 ft).

Lower unit: pale-brown, thin-bedded to laminated, 

gypsiferous, shaly siltstone and mudstone. Thickness: 

98–130 m (320–430 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Lower part forms ledgy cliff. 

Upper part forms steep slope with scattered ledges.

Abandoned Mineral Lands and Potential Mining 

Activity. TRmu is at the surface of some abandoned 

mines. 

Triassic Period: Fluvial Systems in a Tropical Climate. 

Tropical climate conditions dominated the region in the 

Early Triassic. The western part of the Colorado Plateau 

consisted of a broad continental shelf while nearshore to 

coastal environments developed in the eastern part of the 

plateau. Sediments spread into Utah from the erosion of 

the Ancestral Rocky Mountains in Colorado. TRm

represents deposition in tidal-flat, sabkha, and low coastalplain environments. 

Rocks from the Middle and Late Permian Epochs (272–252 million years ago) are not mapped within Glen Canyon National Recreation Area. 

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Permian 

Formations

(P)

In the Circle Cliffs area northeast of the Escalante River, 

Permian strata are exposed in the bottoms of several 

deep canyons. See separate descriptions below.

Mapped on sheet 2 (in pocket).

See individual Permian units. See individual Permian units. See individual Permian units.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 11 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Kaibab 

Formation 

(Pk) 

Gray, thin-bedded dolomite, dolomitic limestone, and 

sandy dolomitic limestone with thin interbeds of 

calcareous siltstone. Includes chert nodules and layers in 

the upper part. Thickness: 70 m (235 ft) at Navajo 

Bridge near Lees Ferry. Pk thins to the east (probably 

due to erosion prior to deposition of TRm). Mapped in 

the Lees Ferry area.

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms cliffs.

Paleontological Resources. None reported in the 

recreation area, but on the Colorado Plateau, Pk

commonly contains abundant fossils of marine 

invertebrates including brachiopods, corals, bryozoans, 

and crinoids.

Landscape Safety Hazards. Documented fall from Pk

cliff. 

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from Pk have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. By the end of the Permian, the 

major land masses were suturing together to form the 

supercontinent Pangea. Pk represents a marine 

transgression across the region.

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Toroweap 

Formation 

(Pt) 

Gray and brown, fine-grained, silty sandstone, silty 

mudstone, and cherty limestone. Exposed and mapped 

only south of Navajo Bridge near Lees Ferry. Thickness: 

55–67 m (180–220 ft). 

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes. None reported.

Pennsylvanian and Permian Periods: Shallow Seas 

and Assembling Pangea. By the end of the Permian, the 

major land masses were suturing together to form the 

supercontinent Pangea. Pt represents nearshore and 

shallow marine deposition along the western margin of 

Pangea

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Coconino 

Sandstone

(Pco) 

Yellowish-gray, medium- to fine-grained, cross-bedded 

sandstone. The uppermost few feet of the formation is 

exposed and mapped only south of Navajo Bridge near 

Lees Ferry. Thickness: 0–9 m (0–30 ft).

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Cliff- to ledge-forming.

Sedimentary Rocks and Sedimentary Rock 

Features. Cross-bedding.

Abandoned Mineral Lands and Potential Mining 

Activity. Oil and Gas Exploration: major hydrocarbon 

reservoir in the Paradox Basin of southeast Utah.

Pennsylvanian and Permian Periods: Shallow Seas 

and Assembling Pangea. By the end of the Permian, the 

major land masses were suturing together to form the 

supercontinent Pangea. Pco represents coastal and 

nearshore marine deposition along the western margin of 

Pangea.

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Hermit 

Formation 

(Phe) 

Dark brownish-red, thin-bedded siltstone and shale with 

thin beds of lighter colored, fine-grained sandstone. 

Only the upper part is exposed in the map area south of 

Navajo Bridge. Thickness: about 195 meters (640 ft).

Mapped on sheets 2 and 3 (in pocket).

Landscape Features. Forms slopes. None reported. Not mapped in Glen Canyon National Recreation Area.

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Cutler Group

White Rim 

Sandstone

(Pwr) 

Gray, fine- to coarse-grained, cross-bedded sandstone, 

silty sandstone, and locally dolomitic sandstone. 

Thickness: 0–26 m (0–85 ft) in the Hite area, where it 

thickens rapidly to the north and northwest and thins 

and pinches out to the south and east, and 9 m (30 ft) 

at Nokai Dome along the San Juan arm, where it thins 

eastward.

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms a cliff and broad bench 

that makes a prominent marker bed throughout the 

region.

Sedimentary Rocks and Sedimentary Rock 

Features. High-angle cross-bedding.

Unusual Sedimentary Rock Features. Tafoni.

Paleontological Resources. Although rare, trace 

fossils have been reported from Canyonlands National 

Park.

Unconformities. TR-1 separates Pwr from TRm.

Economic Minerals. Main unit containing tar sands in 

the Tar Sand Triangle.

Geologic Type Sections. Designated in Canyonlands 

National Park adjacent to the northern arm of the 

recreation area.

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from Pwr have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Abandoned Mineral Lands and Potential Mining 

Activity. Tar Sands Exploration: contains significant tar 

sand deposits. Abandoned cabins from the drilling of a tar 

sands oil well.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. Pwr was deposited in a 

mostly eolian environment with some marine influence.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 12 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Cutler Group

Organ Rock 

Formation 

(Po) 

Brown to grayish-red, horizontally bedded siltstone 

interbedded with sandstone and mudstone beds. Local 

lenses of coarse conglomerate in the upper part erode 

out in relief. Much less resistant than Pcm. Thickness: 

67–140 m (220–460 ft). Thins to the north.

Mapped on sheets 1, 2, and 3 (in pocket).

Landscape Features. Forms broad slope or bench that 

gradually steepens up-section to form steep ledgy 

slopes and small cliffs. 

Sedimentary Rocks and Sedimentary Rock 

Features. High-angle cross-bedding (eolian features). 

Trough-shaped cross-bedding, coarse conglomerate, 

and mudstone (fluvial features).

Paleontological Resources. Potential fossils in the 

stream channel deposits. 

Unconformities. TR-1 separates Po from TRmh.

Unconsolidated Surficial Deposits. Slope movement 

deposits (rock slides, landslides, and slumps).

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from Po have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. Po was deposited in 

floodplain, tidal mud-flat, and beach environments that 

would develop during marine transgressions. Coarse 

conglomerate lenses are characteristic of high-energy 

stream channel deposits. 

LOWER PERMIAN

or Cisuralian 

Epoch

(299–272 mya)

Cutler Group

Cedar Mesa 

Sandstone

(Pcm) 

Yellowish-gray, reddish-orange, and reddish-brown, 

cross-bedded, fine-grained sandstone interbedded with 

lenses of reddish-brown to grayish-green sandy siltstone. 

Siltstone increases in upper part. Thickness: 290–335 m 

(980–1100 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Forms massive cliffs with 

scattered ledges, mesas, and slickrock. Alcoves.

Sedimentary Rocks and Sedimentary Rock 

Features. High-angle cross-bedding (eolian features) 

and fluvial (floodplain) features. Convoluted bedding 

common.

Paleontological Resources. Tracks of the skink, 

Anomalopus, and its prey, the beetle Stenichus, as well 

as tracks of synapsids.

Geologic Type Sections. Cedar Mesa, which extends 

north of the San Juan Arm.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. Pcm was deposited in 

coastal eolian environments that were occasionally overrun 

by small rivers or streams, floodplains, and playas (Po). 

Marine incursions occurred in the northern areas. 

UPPER 

PENNSYLVANIAN 

to LOWER

PERMIAN

(307–272 mya)

Cutler Group

Cutler Formation

(Pc) 

Cutler Group strata grade northward into a thick 

sequence of interbedded arkosic sandstone and 

mudstone along the Green River in the northeast part of 

the map area, and individual formations become 

unrecognizable. In that area, the Cutler Group becomes 

the Cutler Formation and does not have any formal 

members. Thickness: about 180 meters (600 ft).

Mapped on sheets 1 and 2 (in pocket).

None reported. None reported.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Erosion of the adjacent Uncompahgre 

highlands to the northeast shed arkosic (feldspar-rich) 

sediments into the margins of the Paradox Basin, and 

these sediments interbedded with marine units. Restricted 

marine conditions gave way to open-marine environments.

UPPER 

PENNSYLVANIAN 

to LOWER 

PERMIAN

(307–272 mya)

Cutler Group

Lower Cutler 

beds

(PPNcl) 

Brown, orange, and gray, thin- to thick-bedded, fine- to 

coarse-grained sandstone interbedded with lesser 

siltstone, mudstone, conglomerate, and limestone beds. 

Alternating light (quartzitic) and dark (arkosic) sandstone 

beds give unit a banded appearance. Best exposed in 

lower Cataract Canyon from upstream of Hite Crossing 

to the border of Canyonlands National Park. PPNcl are 

called PPNe in Canyonlands National Park and PPNh in 

the San Juan River area. Thickness: 115–140 m (375–

460 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Forms a ledgy slope.

Paleontological Resources. Marine invertebrate fossils 

of foraminifera, brachiopods, bivalves, gastropods, 

crinoids, and elasmobranch teeth.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. PPNcl, PPNhg, and PPNe

record deposition in tidal flat, delta, coastal sand dune, 

fluvial, and shallow-marine shelf environments. 
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 13 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER 

PENNSYLVANIAN 

to LOWER 

PERMIAN

(307–272 mya)

Cutler Group

Halgaito 

Formation, 

upper and lower 

members

(PPNhgu, 

PPNhgl) 

Interbedded reddish-brown, grayish-red, and yellowishred, very fine to medium-grained sandstone, dark-red 

siltstone. Exposures along the San Juan River are 

mapped as two informal members.

Upper member: locally very minor to no carbonate beds 

exposed on the surface. Thickness: 18–27 m (60–90 ft).

Lower member: includes thin beds of gray cherty 

fossiliferous limestone and dolomite. Thickness: about 

116 m (380 ft).

Thickness: 142 m (465 ft) at Johns Canyon near the San 

Juan River.

Mapped on sheet 2 (in pocket).

Landscape Features. Forms steep ledgy slopes.

Sedimentary Rocks and Sedimentary Rock 

Features. Cyclic interbeds of fossiliferous marine 

limestone, siltstone, sandstone, black organic shale, 

dolomite, and/or gypsum characteristic of fluctuating 

sea level and nearshore marine depositional 

environments.

Paleontological Resources. Marine fossils include 

foraminifera, crinoids, algal mats, burrows, and bones 

from fish, amphibians (including the “sail back” 

Platyhystrix), tetrapods, reptiles, and pelycosaurs.

Geologic Type Sections. Unofficially named for 

Halgaito Spring, southwest of Mexican Hat.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. PPNcl, PPNhg, and PPNe

record deposition in tidal flat, delta, coastal sand dune, 

fluvial, and shallow-marine shelf environments. 

UPPER 

PENNSYLVANIAN 

to LOWER 

PERMIAN

(307–272 mya)

Cutler Group

Elephant 

Canyon 

Formation 

(PPNe) 

Cyclically interbedded gray, planar, medium- to very 

thick- bedded fossiliferous limestone, poorly exposed 

brown to gray siltstone, very fine- grained sandstone, 

and calcareous mudstone. Thickness: about 120 m (400 

ft) exposed along the Green River.

Mapped on sheets 1 and 2 (in pocket).

Sedimentary Rocks and Sedimentary Rock 

Features. Fossiliferous limestone. 

Paleontological Resources. Marine invertebrate fossils 

include foraminifera, crinoids, corals, conodonts, 

bryozoans, brachiopods, trilobites, cephalopods, and 

echinoderms.

Geologic Type Sections. Elephant Canyon in 

Canyonlands National Park.

None reported.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. PPNcl, PPNhg, and PPNe

record deposition in tidal flat, delta, coastal sand dune, 

fluvial, and shallow-marine shelf environments. 

UPPER 

PENNSYLVANIAN 

(307–299 mya)

Hermosa 

Group

Honaker Trail 

Formation 

(PNht) 

Cyclically interbedded gray limestone, brown to gray 

siltstone to very fine grained sandstone, and dark gray 

to black organic shale. The upper contact is placed at 

the top of the highest prominent, laterally continuous 

limestone bed, which can be up to 6 m (20 ft) thick. In 

the San Juan Arm area, this limestone bed forms a 

bench beneath slope-forming PPNcl beds. A prominent 

ledge-forming sandstone bed informally called the 

Goodrich Sandstone directly overlies the upper 

limestone throughout most of the map area, forming a 

distinctive double-ledge with the PNht contact between 

the two ledges. Thickness: 218 m (715 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Forms ledges and smaller cliffs 

separated by short slopes of organic shale.

Sedimentary Rocks and Sedimentary Rock 

Features. Cyclic interbeds of fossiliferous marine 

limestone, siltstone, sandstone, black organic shale, 

dolomite, and/or gypsum characteristic of fluctuating

sea level and nearshore marine depositional 

environments.

Paleontological Resources. Marine invertebrate fossils 

include foraminifera, bryozoans, gastropods, crinoids, 

and conodonts. Trace fossils include root traces, pellets, 

and borings.

Unconsolidated Surficial Deposits. Slope movement 

deposits (rock slides, landslides, and slumps).

Geologic Type Sections. Honaker Trail in The 

Goosenecks section of the San Juan River.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Abandoned Mineral Lands and Potential Mining 

Activity. Oil and Gas Exploration: major hydrocarbon 

reservoir in the Paradox Basin of southeast Utah.

Pennsylvanian and Permian Periods: Shallow Seas 

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. PNht records deposition in 

shallow marine, beach, lagoonal, and deltaic 

environments. 
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Bedrock Map Unit Properties Table: Glen Canyon National Recreation Area, page 14 of 14

Age

(mya=millions 

of years ago)

Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

UPPER 

PENNSYLVANIAN 

(307–299 mya)

Hermosa 

Group

Honaker Trail 

Formation, 

upper and lower 

members

(PNhtu, PNhtl)

Informal upper (PNhtu) and lower (PNhtl) members are 

mapped in the San Juan River Arm. Gradational contact.

Upper member: red mudstone. Thickness: 49–55 m 

(160–180 ft).

Lower member: gray and black shale. Thickness: 163–

169 m (535–555 ft).

Mapped on sheet 2 (in pocket).

Landscape Features. Upper member: forms slopes.

Lower member: forms slopes. None reported.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions gave way 

to open-marine environments. PNht records deposition in 

shallow marine, beach, lagoonal, and deltaic 

environments.

MIDDLE 

PENNSYLVANIAN 

(315–307 mya)

Hermosa 

Group

Paradox 

Formation 

(PNp) 

Gray lime mudstone, spiculiferous wackestone, 

fossiliferous and peloidal wackestone and packstone, 

algal boundstone, and cross-bedded ooid grainstone 

cyclically interbedded with brown to gray siltstone to 

very fine grained sandstone, dark-gray to black organic 

shale, and (in Cataract Canyon only) contorted gray 

gypsum. Sandstone is planar to trough cross-bedded 

and has fossil fragments. Shale is fossil-poor, laminated 

to thinly laminated, highly organic, and locally sulfurous. 

Cycles are typically 2–6 m (6–20 ft) thick. Exposed in the 

deepest parts of Cataract Canyon and San Juan River 

Arm and are some of the most studied Pennsylvanian 

rocks in Utah. The upper contact in San Juan River Arm 

is placed at the top of a massive blocky cliff known as 

“The Horn limestone” that forms the most recognizable 

horizon in the area. Thickness: exposed strata are too 

contorted to measure, but the estimated thickness is 60 

m (200 ft).

Mapped on sheets 1 and 2 (in pocket).

Landscape Features. Forms cliffs.

Sedimentary Rocks and Sedimentary Rock 

Features. Cyclic interbeds of fossiliferous marine 

limestone, siltstone, sandstone, black organic shale, 

dolomite, and/or gypsum characteristic of fluctuating 

sea level and nearshore marine depositional 

environments. Trough-shaped cross-beds in sandstone 

beds.

Paleontological Resources. Potential marine 

invertebrate fossils include crinoids, bryozoans, 

brachiopods, fusulinids, corals, foraminifers, and 

conodonts. Although not found in the recreation area 

yet, PNp also contains sponge spicules, algae, ooids, 

fish fragments, and scattered distinctive algal 

boundstone mounds composed of phylloid algal plates 

that appear like mounds of crushed potato chips. 

Unconsolidated Surficial Deposits. Slope movement 

deposits (rock slides, landslides, and slumps).

Paleontological Resources Inventory, Monitoring, 

and Protection. Fossils from PNp have not yet been 

documented from Glen Canyon National Recreation Area 

but could be present.

Abandoned Mineral Lands and Potential Mining 

Activity. Oil and Gas Exploration: major hydrocarbon 

reservoir in the Paradox Basin of southeast Utah, and the 

primary producing reservoir in the Greater Aneth Oil Field 

of southeastern Utah.

Pennsylvanian and Permian Periods: Shallow Seas

and Assembling Pangea. Tectonic compression caused 

the northwest–southeast trending Paradox Basin to 

subside, resulting in episodes of marine incursions into 

southeastern Utah. Restricted marine conditions eventually 

gave way to open-marine environments. PNp records 

cycles of transgressions and regressions, and the 

subsequent strata of porous limestone, shale, and salt 

resulted in economic reserves of hydrocarbons in the 

Paradox Basin.

Rocks older than Middle Pennsylvanian are not mapped within Glen Canyon National Recreation Area. 
 Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 1 of 6 

Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area 

Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Holocene)

Man Made 

Deposits

Artificial fill and 

disturbed areas

(Qfd) 

Gravel, sand, and earth-fill emplaced by humans and large 

areas that have been significantly disturbed. Thickness is 

highly variable, but generally 0–18 m (0–60 ft) thick.

Mapped on sheets 2 and 3 (in pocket).

Construction of Glen Canyon Dam and other disturbed 

areas (not natural geologic features or processes).

Abandoned Mineral Lands and Potential Mining 

Activity. Gravel pits.

Glen Canyon National Recreation Area And Other 

NPS Areas Along The Colorado River. Construction of 

Glen Canyon Dam and other development in the region 

resulted in disturbed areas.

QUATERNARY

(Holocene)

Man Made 

Deposits

Concrete fill in Glen 

Canyon Dam

(Qfdm) 

Concrete fill (3,745,000 m3; 4,901,000 yds3) used to create 

Glen Canyon Dam. Dam dimensions are in the

glca_geology.pdf. 

Mapped on sheets 2 and 3 (in pocket).

Construction of Glen Canyon Dam and other disturbed 

areas (not natural geologic features or processes). None reported.

Glen Canyon National Recreation Area And Other 

NPS Areas Along The Colorado River. Construction of 

Glen Canyon Dam and other development in the region 

resulted in disturbed areas.

QUATERNARY

(Upper Pleistocene to 

Holocene)

Alluvial Deposits

Undifferentiated 

alluvial deposits

(Qa) 

Boulder to pebble gravel, sand, silt, and clay deposited in 

small drainages, in stream and wash channels, on broad 

alluvial fan surfaces, and in terrace remnants. Poorly to 

moderately well sorted. Thickness: 0–15 m (0–50 ft). Mostly 

correlates with deposits mapped as Qal, Qal1, Qat, Qat2-3, 

Qag, Qae, Qaec, and Qea in other areas.

Mapped on sheets 2 and 3 (in pocket).

See individual units. See individual alluvial units. 

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY

(Upper Pleistocene to 

Holocene)

Alluvial Deposits

Alluvial river and 

major stream 

deposits

(Qal) 

Similar to Qal1 deposits but more generalized and only found 

in the northern part of the map area. Locally includes 

sediments equivalent to Qat2 and possibly Qat3. 

Mapped on sheets 1 and 2 (in pocket).

Unconsolidated Surficial Deposits. With thirty-three 

mapped alluvial and mixed alluvial units, alluvial deposits 

are the most diverse surficial deposits in the recreation 

area.

Flash Floods and Debris Flows. Intense thunderstorms 

may cause flash floods and debris flows, which may 

threaten visitor safety and damage or destroy 

infrastructure. 

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY 

(Upper Pleistocene to Holocene)

Alluvial Deposits

Young alluvial river 

and major stream 

deposits

(Qal1) 

Lenticular, interbedded gravel, sand, silt, and clay deposited 

by the San Juan and Colorado Rivers and larger tributaries. 

Generally poor to well sorted. Rounded clasts show evidence 

of significant transport. May include poorly sorted debris flow 

deposits and talus derived from side canyons and cliffs. 

Typically, deposits are up to 6 m (20 ft) above the river and 

stream channels, but can contain modern human-made debris 

up to 12 m (40 ft) above the modern river. Thickness: 0–9 m

(0–30 ft). 

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Small-scale trough 

cross-bedding, climbing ripple laminations, and imbricated 

cobbles. Forms sand and gravel bars in river channels and 

point bars on meander bends.

Slope Movement Hazards and Risk. Talus indicates 

where rockfalls have occurred in the past and are likely to 

occur again.

Flash Floods and Debris Flows. Intense thunderstorms 

may cause flash floods and debris flows, which may 

threaten visitor safety and damage or destroy

infrastructure.

Abandoned Mineral Lands and Potential Mining 

Activity. Placer gold mines.

Glen Canyon Dam and Downstream Impacts to the 

Colorado River. Sandbars and pre-dam flood deposits 

have been eroded, and the thin point bars that formed at 

meander bends may eventually disappear. 

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

 Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 2 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Upper Pleistocene to 

Holocene)

Alluvial Deposits

Young alluvial river 

and stream terrace 

gravel deposits

(Qaty) 

Pebble- to cobble-gravel with less common boulders, sand, 

silt, and clay. River deposits preserved as terraces. Most clasts 

are moderately to well sorted, rounded, and originated 

primarily from outside the map area. In the Escalante area, 

Qaty contains many deposits mapped as Qat2–13. 

Mapped on sheet 2 (in pocket).

Unconsolidated Surficial Deposits. Remnants of 

previous terraces. None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY 

(Lower Pleistocene to Holocene)

Alluvial Deposits

Undifferentiated 

alluvial river and 

stream terrace 

gravel deposits

(Qat, Qat2–13, 

Qatg8–10, 

Qatg12) 

Qat. Terrace deposits of pebble- to cobble-gravel with less 

common boulders, sand, silt, and clay. Most clasts are 

moderately to well sorted, rounded, and originated primarily 

from outside the map area. The many terrace levels range

from about 6 m (20 ft) to about 400 m (1,400 ft) above the

modern river channel. Lake Powell covers lower deposits.

Qat2. Level 2 (Holocene; possibly locally late middle 

Pleistocene)

Qat3. Level 3 (lower Holocene to upper Pleistocene)

Qat4. Level 4 (Middle to Upper Pleistocene)

Qat5. Level 5 (Middle to Upper Pleistocene)

Qat6. Level 6 (Lower to Middle Pleistocene)

Qat7. Level 7 (Middle Pleistocene)

Qat8. Level 8 (Lower to Middle Pleistocene)

Qat9. Level 9 (Lower to Middle Pleistocene)

Qat10. Level 10 (Lower to Middle Pleistocene)

Qat11. Level 11 (Lower to Middle Pleistocene)

Qat12. Level 12 (Lower to Middle Pleistocene)

Qat13. Level 13 (Lower to Middle Pleistocene)

Qatg8. Qat8 and locally derived gravel deposits. (Lower to 

Middle Pleistocene)

Qatg9. Qat9 and locally derived gravel deposits. (Lower to 

Middle Pleistocene)

Qatg10. Qat10 and locally derived gravel deposits. (Lower to 

Middle Pleistocene)

Qatg12. Qat12 and locally derived gravel deposits. (Lower to 

Middle Pleistocene)

Qat is mapped on sheets 1, 2, and 3 (in pocket). Numbered

alluvial and stream terrace gravel deposits are mapped on 

sheets 2 and 3. Qat5 and Qat6 are both mapped on all three 

sheets.

Unconsolidated Surficial Deposits. Remnants of 

previous terraces, channel deposits, and alluvial fanshaped deposits.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY

(Lower Pleistocene to 

Holocene)

Alluvial Deposits

Undifferentiated 

locally derived 

alluvial gravel 

deposits

(Qag) 

Poorly to moderately well sorted, boulder- to clay-sized 

deposits preserved as remnants above small ephemeral 

streams and washes, on gentle to moderate slopes, and on 

broad sloping benches. Some boulders are up to 2 m (6 ft) in 

diameter. Clasts derived from local bedrock. Eolian silt and 

sand has accumulated on some older deposits. Generally 

found at lower levels. Thickness: 0–18 m (0–60 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Remnants of 

previous terraces, channel deposits, and alluvial fanshaped deposits.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 3 of 6

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Middle to Upper

Pleistocene)

Alluvial Deposits

Intermediate-level 

locally derived 

alluvial gravel 

deposits

(Qagm)

Similar lithology to Qag, but Qagm is found on benches and 

slopes 6–30 m (20–100 ft) above the floor of small streams 

and washes, but still within the canyons.

Mapped on sheet 3 (in pocket).

Unconsolidated Surficial Deposits. Remnants of 

previous terraces, channel deposits, and alluvial fanshaped deposits.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY

(Lower to Middle 

Pleistocene)

Alluvial Deposits

High-level locally 

derived alluvial 

gravel deposits

(Qago)

Similar lithology to Qag, but Qago deposits cap high, gently 

sloping benches and knolls up to about 430 m (1,400 ft) 

above the floor of adjacent small streams and washes.

Mapped on sheets 2 and 3 (in pocket).

Unconsolidated Surficial Deposits. Remnants of 

previous terraces, channel deposits, and alluvial fanshaped deposits.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Clasts in alluvial 

deposits reflect erosion of local bedrock as well as fartravelled bedrock from western Colorado.

QUATERNARY

(Holocene)

Mixed 

Environment 

Deposits

Young alluvial and 

eolian deposits

(Qae)

Heterogeneous mixture of boulders- to pebbles, sand, silt, and 

clay covered by minor to moderate amounts of windblown 

sand and silt. Similar to Qa and Qac, Qae clasts are 

composed of local or upslope lithologies. Rockfalls, landslides, 

and debris flows contribute angular rubble to the deposits. 

Mapped on broader slopes with less-defined drainages than 

Qa and Qac. Qae is mapped in small washes where the clasts 

were deposited in the active part of the wash bottom to 

about 12 m (40 ft) above the wash floor. Thickness: generally 

2–6 m (6–20 ft) thick.

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and eolian sediments. 

Slope Movement Hazards and Risk. Angular rubble

indicates where slope movements have occurred in the 

past and are likely to occur again.

Flash Floods and Debris Flows. Intense thunderstorms 

may cause flash floods and debris flows, which may 

threaten visitor safety and damage or destroy 

infrastructure.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Holocene)

Mixed 

Environment 

Deposits

Level 2 alluvial and 

eolian deposits

(Qae2)

Similar lithology to Qae, but Qae2 deposits are 6–12 m (20–

40 ft) above the adjacent wash.

Mapped on sheets 2 and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and eolian sediments. None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Upper Pleistocene 

to Holocene)

Mixed 

Environment 

Deposits

Level 3 alluvial and 

eolian deposits

(Qae3)

Similar lithology to Qae, but Qae3 deposits are 12–24 m (40–

80 ft) above the adjacent wash.

Mapped on sheets 1 and 2 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and eolian sediments. None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

 Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 4 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Upper Pleistocene 

to Holocene)

Mixed 

Environment 

Deposits

Alluvial and colluvial 

deposits

(Qac) 

Deposits consisting of boulders to clay-sized sediment. 

Contains windblown sand and silt and colluvium derived from 

adjacent slopes. Moderately to poorly sorted. Rockfalls, 

landslides, and debris flows contribute large angular boulders. 

Similar to Qa and Qae except for more colluvium. Thickness: 

0–6 m (0–20 ft). 

Mapped on sheets 2 and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and colluvial sediments.

Slope Movement Hazards and Risk. Colluvium indicates 

where slope movements have occurred in the past and are 

likely to occur again.

Flash Floods and Debris Flows. Intense thunderstorms 

may cause flash floods and debris flows, which may 

threaten visitor safety and damage or destroy 

infrastructure.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Middle Pleistocene 

to Holocene)

Mixed 

Environment 

Deposits

Alluvial fan, stream, 

eolian, and colluvial 

deposits

(Qaec) 

Boulders, sand, to clay deposited as alluvial fan, ephemeral 

stream, and colluvial deposits on low-relief slopes and 

benches, especially below cliff- and ledge-forming bedrock 

units, and in poorly developed terraces along ephemeral 

streams. Commonly includes talus and rockfall debris. Farthest 

ends of deposit transition into Qes. Thickness: 0–10 m (0–30 

ft). 

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial, 

colluvial, and eolian sediments.

Slope Movement Hazards and Risk. Colluvium and 

talus indicate where rockfalls have occurred in the past 

and are likely to occur again.

Flash Floods and Debris Flows. Intense thunderstorms 

may cause flash floods and debris flows, which may 

threaten visitor safety and damage or destroy 

infrastructure. 

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Middle Pleistocene 

to Holocene)

Mixed 

Environment 

Deposits

Eolian and alluvial 

deposits

(Qea) 

Moderately to very well sorted sand, silt, and clay. Deposited 

by wind and locally reworked by water. Commonly capped by 

thick calcic soil (caliche) that forms a resistant bench. 

Common on broad stable surfaces. Similar to Qes, but 

evidence of alluvial activity is common and dune forms are less 

common. Thickness: 0–15 m (0–50 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of winddeposited sand, silt, and clay mixed with stream-deposited 

pebbles and cobbles.

Human disturbances can lead to migrating windblown 

sand.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Lower Pleistocene 

to Holocene)

Mixed 

Environment 

Deposits

Older eolian and 

alluvial deposits

(Qeao) 

Similar lithology to Qea but Qeao deposits are mapped on 

the highest benches and have the thickest calcic soil.

Mapped on sheets 2 and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of winddeposited sand, silt, and clay mixed with stream-deposited 

pebbles and cobbles.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Middle to Upper

Pleistocene)

Mixed 

Environment 

Deposits

Older alluvial and 

colluvial deposits

(Qaco) 

Similar lithology to Qac, but these older deposits are incised 

by active washes and form inactive terraces and benches 6 m 

to more than 30 m (20–100+ ft) above washes.

Mapped on sheet 2 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and colluvial sediments.

Slope Movement Hazards and Risk. Colluvium indicates 

where slope movements have occurred in the past and are 

likely to occur again.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 

QUATERNARY

(Lower to Upper

Pleistocene)

Mixed 

Environment 

Deposits

Older alluvial and 

eolian deposits

(Qaeo) 

Similar lithology to Qae, but Qaeo deposits are 9 to >470 m 

(30–1,550+ ft) above the adjacent wash.

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Mixture of alluvial 

and eolian sediments. None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. As the Colorado River and 

associated tributaries continued to incise bedrock, previous 

channels became elevated terraces. Alluvial deposits mixed

with wind-blown sand and silt. 
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

 Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 5 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Middle Pleistocene 

to Holocene)

Lacustrine 

deposits

Lacustrine deposits

(Ql) 

Thinly laminated silt, very fine grained sand, peat, and clay. 

Estimated to be 0–10 m (0–30 ft) thick in the Good Hope Bay 

area. Thick deposits in Lake Canyon are remnants of a lake 

that the Piute Indians called Pagahrit, which drained in CE 

1915. The lake consists of several lake cycles, the oldest of 

which has been dated at 5,180 years before present.

Mapped on sheets 1 and 2 (in pocket).

Unconsolidated Surficial Deposits. Layers of sand, silt, 

clay, and peat. Several lake cycles record the history of 

ancient Lake Pagahrit. 

Paleontological Resources. Pollen, peat, and insects that 

provide paleoclimate information have been retrieved from 

the Lake Pagahrit site in the Lake Canyon area.

Paleontological Resources Inventory, Monitoring, 

and Protection. Protocols to monitor paleontological 

resources have been defined and management is in the 

process of completing an inventory of fossil sites in the 

recreation area and establishing a systematic monitoring 

plan and database.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon.

QUATERNARY

(Middle Pleistocene 

to Holocene)

Precipitated 

Deposits

Spring tufa deposits

(Qst) 

Pale-gray, yellowish-gray, and reddish-gray tufa (calcium 

carbonate) deposited by springs. Cements bedrock and talus 

rubble, colluvium, and other surficial deposits. In many 

canyons below seeps and springs, tufa can be up to 1–2 m 

(0.3–0.6 ft) thick. In Red Canyon, deposits are as much as 5 m 

(15 ft) thick.

Mapped on sheets 1 and 2 (in pocket).

Unconsolidated Surficial Deposits. Chemical 

sedimentary rock composed of calcium carbonate. Formed 

by evaporation.

None reported.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. With exposure of the Jn/Jk

contact, groundwater seeps and springs develop along the 

canyon walls and calcium carbonate is precipitated.

QUATERNARY

(Middle Pleistocene to 

Holocene)

Eolian Deposits

Eolian sand

(Qes) 

Very well-sorted, well-rounded, mostly fine- to mediumgrained, frosted (translucent) quartz sand derived from the 

weathering of sandy bedrock, especially Navajo Sandstone 

(Jn). Thickness: 0–15 m (0–45 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Wind-blown 

sediment deposited in sheets, mounds, and dunes. 

Primarily derived from weathered Jn and Je.

Human disturbances can lead to migrating windblown 

sand.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Uplift continued into the 

Holocene and eolian processes transported weathered 

quartz grains from exposed Mesozoic and Paleozoic 

sandstones and deposited them in sand sheets, mounds, 

and small dunes in protected areas. Amount of sand 

generation and transport is probably related to short- and 

long-term climatic fluctuations.

QUATERNARY

(Historical) 

Mass Movement 

Deposits

Historical landslides 

and slump deposits

(Qmsh) 

Chaotic, extremely poorly sorted, angular, massive blocks to 

clay-size material that slumped or flowed down slopes. The 

deposits range from surficial talus and alluvium to blocks of 

bedrock several hundred meters across. Thickness is poorly 

known and highly variable, ranging from 0–75 m (0–250 ft), 

but locally may exceed 100 m (300 ft). Qmsh represents slides 

and slumps that show evidence of historic movement.

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Variety of slope 

movement deposits including slides, slumps, earthflows, 

and toreva blocks, which are landslides that occur when 

erosion of weaker material, such as shale, undercuts 

stronger material, such as sandstone.

Slope Movement Hazards and Risk. Landslides and 

slumps occur nearly everywhere the Chinle Formation is 

exposed above or just below the water line of Lake Powell, 

but locally may also involve other formations. Landsliding 

and slumping have been greatly accelerated along the 

shore of Lake Powell, but have and can impact other 

areas, as well. Even historical landslides remain unstable 

and can be reactivated under certain conditions. All 

landslides and mass movement deposits may continue to 

move by slow creep and pose a risk of renewed 

movement.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.

QUATERNARY

(Lower Pleistocene to 

Holocene)

Mass Movement 

Deposits

Landslides and 

slump deposits

(Qms) 

Chaotic, extremely poorly sorted, angular, massive blocks to 

clay-size material that slumped or flowed down slopes. The 

deposits range from surficial talus and alluvium to blocks of 

bedrock several hundred meters across. Thickness is poorly 

known and highly variable, ranging from 0–75 m (0–250 ft), 

but locally may exceed 100 m (300 ft). May include historic 

movement.

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Generally forms 

large coalescing landslide complexes that extend as a 

continuous apron up to several kilometers. Upper surfaces 

are typically hummocky.

Slope Movement Hazards and Risk. Landslides and 

slumps occur nearly everywhere the Chinle Formation is 

exposed above or just below the water line of Lake Powell, 

but locally may also involve other formations. Even 

historical landslides remain unstable and can be 

reactivated under certain conditions. All landslides and 

mass movement deposits may continue to move by slow 

creep and pose a risk of renewed movement.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.
Colored map units are mapped within Glen Canyon National Recreation Area. Bold text refers to sections in report. Refer to the glca_geology.pdf in the GRI GIS data for detailed geologic descriptions and additional information.

 Unconsolidated Map Unit Properties Table: Glen Canyon National Recreation Area, page 6 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY

(Lower Pleistocene 

to Holocene)

Mass Movement 

Deposits

Slump blocks

(Qmsb) 

Blocks of bedrock, some as much as 2.7 km (1.5 mi) long, that 

have slumped downslope, especially blocks of Wingate 

Sandstone (JTRw) that have slumped onto the underlying 

Chinle Formation (TRc). Mapped separately from Qms and

Qmst only in the White Canyon area. Thickness: highly 

variable.

Mapped on sheets 1 and 2 and 3 (in pocket).

Unconsolidated Surficial Deposits. Typically, blocks of 

Qmsb have rotated backwards and dip toward the nearby 

cliff.

Slope Movement Hazards and Risk. Weathering and 

erosion of less resistant material results in cliff collapse, 

rockfalls, and slides. Probably less active today than in the 

past except near the lake.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.

QUATERNARY

(Lower Pleistocene 

to Holocene)

Mass Movement 

Deposits

Talus deposits

(Qmt) 

Angular rockfall debris at the base of steep slopes. Mapped 

separately from Qmst in the Hite Crossing, Bullfrog, Lees 

Ferry, and San Juan Canyon areas. Thickness: generally less 

than 10 m (30 ft).

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Jumbled blocks of 

rock. Commonly at the base of all ledges, cliffs, and steep 

slopes.

Slope Movement Hazards and Risk. Qmt may become 

unstable and begin to slide down slope with increased 

precipitation. Rockfalls can occur in any steep area and are 

highly unpredictable.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.

QUATERNARY

(Lower Pleistocene 

to Holocene)

Mass Movement 

Deposits

Landslide, slump, 

and talus deposits, 

undifferentiated

(Qmst) 

Undifferentiated deposits of Qms, Qmsh, Qmsb, Qmt, and 

Qmte. 

Mapped on sheets 1 and 2 (in pocket).

See individual units. See individual units.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.

QUATERNARY

(Lower Pleistocene 

to Holocene)

Mass Movement 

Deposits

Talus deposits with 

eolian sand mantle

(Qmte) 

Qmt deposits that are mostly covered by sand. Sand can be as 

much as 9 m (30 ft) thick in some areas. Some Qmte is not 

mapped separately from Qmt. 

Mapped on sheets 1, 2, and 3 (in pocket).

Unconsolidated Surficial Deposits. Jumbled blocks of 

rock with a covering of wind-blown sand.

Slope Movement Hazards and Risk. Qmt may become 

unstable and begin to slide down slope with increased 

precipitation. Talus also indicates where rockfalls have 

occurred in the past and are likely to occur again.

Paleogene–Quaternary Periods: Colorado River 

System And Carving Glen Canyon. Uplift of the 

Colorado Plateau during the Paleogene caused widespread 

erosion. About 5.5 million years ago, the Colorado River 

began to carve Glen Canyon. Entrenched meanders and 

cliffs developed, along with landslides, slumps, and other 

slope movement deposits.