Devils Tower National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/046 

National Park Service 

U.S. Department of the Interior 

Natural Resource Program Center 
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NPS Photos by: Deanna Greco NPS Photos by: Deanna Greco 
Devils Tower National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/046 

Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, Colorado 80225 

September 2008 

U.S. Department of the Interior 

Washington, D.C.
The Natural Resource Publication series addresses natural resource topics that are of interest 

and applicability to a broad readership in the National Park Service and to others in the 

management of natural resources, including the scientific community, the public, and the NPS 

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the information is scientifically credible, technically accurate, appropriately written for the 

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natural resource management information with managerial application. The series targets a 

general, diverse audience, and may contain NPS policy considerations or address sensitive 

issues of management applicability. Examples of the diverse array of reports published in this 

series include vital signs monitoring plans; "how to" resource management papers; 

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sheets; and regularly-published newsletters. 

Views, statements, findings, conclusions, recommendations and data in this report are solely 

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Printed copies of reports in these series may be produced in a limited quantity and they are 

only available as long as the supply lasts. This report is also available online from the Geologic 

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the back cover. 

Please cite this publication as: 

Graham, J. 2008. Badlands National Park Geologic Resource Evaluation Report. Natural 

Resource Report NPS/NRPC/GRD/NRR—2008/046. National Park Service, Denver, 

Colorado. 

NPS D-86, September 2008 
 DETO Geologic Resource Evaluation Report iii 

Table of Contents 

List of Figures .............................................................................................................. iv

Executive Summary ...................................................................................................... 1

Introduction ................................................................................................................... 2

Purpose of the Geologic Resources Evaluation Program...........................................................................................2

Regional Information and Geologic Setting ................................................................................................................2

Park History................................................................................................................................................................3

Geologic Issues............................................................................................................. 8

Rock Climbing ............................................................................................................................................................8

Rockfall.......................................................................................................................................................................8

Redbed erosion rates .................................................................................................................................................9

Paleontology...............................................................................................................................................................9

Gypsum karst .............................................................................................................................................................9

Geologic Features and Processes............................................................................. 13

Devils Tower.............................................................................................................................................................13

Columnar Jointing.....................................................................................................................................................13

Origin of Devils Tower ..............................................................................................................................................13

Map Unit Properties .................................................................................................... 16

Map Unit Properties Table........................................................................................................................................17

Geologic History.......................................................................................................... 19

Precambrian History of the Black Hills Region .........................................................................................................19

Paleozoic History of the Black Hills Region ..............................................................................................................20

Mesozoic History of the Black Hills Region ..............................................................................................................20

Cenozoic History of the Black Hills Region...............................................................................................................22

Glossary....................................................................................................................... 33

References................................................................................................................... 36

Appendix A: Geologic Map Graphic .......................................................................... 39

Attachment 1: Geologic Resource Evaluation Products CD 
iv NPS Geologic Resources Division 

List of Figures 

Figure 1. Location map of Devils Tower National Monument.........................................................................................4

Figure 2. Devils Tower at Devils Tower National Monument..........................................................................................5

Figure 3. Generalized stratigraphic column for units exposed in Devils Tower NM........................................................5

Figure 4. Spearfish Formation........................................................................................................................................6

Figure 5. Devils Tower and view to the northwest with the Missouri Buttes. ..................................................................6

Figure 6. Diagram of the Black Hills dome .....................................................................................................................7

Figure 7. Devils Tower NM Climbing Rangers ascend the leaning column..................................................................10

Figure8. Devils Tower and the leaning column as viewed from the north ....................................................................11

Figure 9. Culverts along Route 10................................................................................................................................12

Figure 10. Devils Tower ...............................................................................................................................................15

Figure 11. Generalized geologic time scale. ................................................................................................................24

Figure 12. Location of the current Black Hills Uplift......................................................................................................25

Figure 13. Plate tectonic schematic illustrating some of the Precambrian tectonic activity ..........................................26

Figure 14. Paleogeographic map of the Late Cambrian...............................................................................................27

Figure 15. Paleogeographic map of North America during the Early Mississippian Period..........................................28

Figure 16. Paleogeographic map of North America during the Early Triassic Period...................................................29

Figure 17. Paleogeographic map of North America during the Jurassic Period ...........................................................30

Figure 18. Western Interior Seaway during the Cretaceous.........................................................................................31

Figure 19. Paleogeography of the Black Hills region near the end of the Laramide Orogeny. .....................................32
 DETO Geologic Resource Evaluation Report 1 

Executive Summary 

This report accompanies the digital geologic map for Devils Tower National Monument in 

Wyoming, which the Geologic Resources Division produced in collaboration with its 

partners. It contains information relevant to resource management and scientific research. 

Devils Tower National Monument has the distinction of 

being the nation’s first national monument, established 

in 1906 by Theodore Roosevelt. The monolithic Devils 

Tower is world renown for its spectacular columnar 

jointing. At 1,546 m (5,070 ft) above mean sea level, 

Devils Tower rises 386 m (1,267 ft) above the Belle 

Fourche River and stands as the most widely recognized 

landmark of the northern Great Plains. 

Geologic issues in Devils Tower National Monument 

include potential rockfalls from two rock units in the 

monument and high erosion rates for some of the 

sedimentary strata. The broad apron of talus 

surrounding Devils Tower attests to rockfall from failure 

along the fractures and joints that define the igneous 

columns of the Tower. Rockfalls also may occur by the 

spalling of rectangular blocks from cliffs of the Hulett 

Sandstone. Rockfalls may perpetuate landslides down 

the hill below the cliffs. 

Permian, Triassic, and Jurassic sedimentary units of red, 

yellow, gray, and green shale; siltstone and sandstone; 

and white gypsum form the rolling hills and gentle slopes 

that surround Devils Tower. The shales and siltstones 

are poorly cemented and erode easily. Because the units 

are so soft, erosion may undercut buildings and roads 

constructed on these units. 

Devils Tower is a bare mass of rock that rises abruptly 

from the surrounding grasslands and pine forests. The 

Tower is about 244 m (800 ft) in diameter at its base 

while its summit measures roughly 55 m (180 ft) from 

east to west and 90 m (300 ft) from north to south. The 

polygonal columns are one of the most striking features 

of Devils Tower. The larger columns taper from a basal 

1.8–2.4 m (6–8 ft) in diameter to about 1.2 m (4 ft) at the 

top. 

The origin of Devils Tower is presently debated. Some 

believe the tower is the remnant of a volcanic neck. 

Others believe the phonolite porphyry that comprises 

the Tower is the remnant of a laccolith or sill. Another 

view holds that the Tower is the remains of a lopolith; 

igneous material that once filled a shallow structural 

depression. 

The Permian, Triassic and Jurassic sedimentary strata 

record a complex depositional history of the Black Hills 

region. Both marine and terrestrial rocks were deposited 

during several episodes of transgressive-regressive 

cycles. The late Cretaceous to Tertiary Laramide 

Orogeny resulted in the uplift of the Black Hills, the 

onset of erosion, and the emplacement of the igneous 

body that would become Devils Tower. In the late 

Tertiary and Quaternary, regional uplift followed by 

erosion by the Belle Fourche River and its tributaries 

resulted in the current topography of Devils Tower. 
2 NPS Geologic Resources Division 

Introduction 

The following section briefly describes the National Park Service Geologic Resource 

Evaluation Program and the regional geologic setting of Devils Tower National 

Monument. 

Purpose of the Geologic Resources Evaluation Program 

The Geologic Resource Evaluation (GRE) Program is 

one of 12 inventories funded under the NPS Natural 

Resource Challenge designed to enhance baseline 

information available to park managers. The program 

carries out the geologic component of the inventory 

effort from the development of digital geologic maps to 

providing park staff with a geologic report tailored to a 

park’s specific geologic resource issues. The Geologic 

Resources Division of the Natural Resource Program 

Center administers this program. The GRE team relies 

heavily on partnerships with the U.S. Geological Survey, 

Colorado State University, state surveys, and others in 

developing GRE products. 

The goal of the GRE Program is to increase 

understanding of the geologic processes at work in parks 

and provide sound geologic information for use in park 

decision making. Sound park stewardship relies on 

understanding natural resources and their role in the 

ecosystem. Geology is the foundation of park 

ecosystems. The compilation and use of natural resource 

information by park managers is called for in section 204 

of the National Parks Omnibus Management Act of 1998 

and in NPS-75, Natural Resources Inventory and 

Monitoring Guideline. 

To realize this goal, the GRE team is systematically 

working towards providing each of the identified 270 

natural area parks with a geologic scoping meeting, a 

digital geologic map, and a geologic report. These 

products support the stewardship of park resources and 

are designed for non-geoscientists. During scoping 

meetings the GRE team brings together park staff and 

geologic experts to review available geologic maps and 

discuss specific geologic issues, features, and processes. 

The GRE mapping team converts the geologic maps 

identified for park use at the scoping meeting into digital 

geologic data in accordance with their innovative 

Geographic Information Systems (GIS) Data Model. 

These digital data sets bring an exciting interactive 

dimension to traditional paper maps by providing 

geologic data for use in park GIS and facilitating the 

incorporation of geologic considerations into a wide 

range of resource management applications. The newest 

maps come complete with interactive help files. As a 

companion to the digital geologic maps, the GRE team 

prepares a park-specific geologic report that aids in use 

of the maps and provides park managers with an 

overview of park geology and geologic resource 

management issues. 

For additional information regarding the content of this 

report and up to date GRE contact information please 

refer to the Geologic Resource Evaluation Web site 

(http://www.nature.nps.gov/geology/inventory/). 

Regional Information and Geologic Setting 

Devils Tower National Monument, in northeast 

Wyoming, is the nation’s the first national monument, 

established by Theodore Roosevelt in 1906 (fig. 1). Devils 

Tower is a steep sided igneous monolith recognized 

worldwide for a spectacular geologic feature known as 

columnar jointing (fig. 2). It is also the most widely 

known landmark of the northern Great Plains. Elevation 

at the relatively flat summit of Devils Tower is 1,560 m 

(5,117 ft) above sea level (Karner and Halvorson 1987, 

1989; Kiver and Harris 1999). The top of the Tower 

measures about 55 m (180 ft) from east to west and about 

91 m (300 ft) from north to south (Robinson 1956). 

Devils Tower rises about 386 m (1,267 ft) above the 

north-flowing Belle Fourche River, which is responsible 

for excavating the buried igneous feature and continues 

to cut away at its south flank. 

The crystalline igneous rock that composes Devils Tower 

is classified as phonolite porphyry. Phonolite is a type of 

fine-grained igneous rock composed primarily of the 

mineral feldspar. A ‘porphyry’ is a rock that has coarse 

crystals surrounded by fine-grained material, or 

groundmass. The groundmass of fresh specimens is lightto dark-gray or greenish-gray and contains conspicuous 

crystals of white feldspar that are about 0.6–1.3 cm (0.25–

0.50 in) in diameter and smaller very dark-green crystals 

of pyroxene, a group of dark rock-forming silicate 

minerals. Weathered surfaces appear light gray or 

brownish gray and lichens may give the phonolite a 

green, yellowish-green, or brown color. 

An apron of talus (eroded blocks lying at the base of the 

cliff), landslide material, and the remnants of a large 

volume of alloclastic breccia (a coarse-grained 

sedimentary rock formed by volcanic processes) 

surround the Tower. Debris from the Tower and the 

Hulett Sandstone Member of the Jurassic Sundance 

Formation comprise the talus and landslide material. The 

talus sheet radiates outward from the tower about 335 m 

(1,100 ft). Near the base of the Tower, talus is about 46 m 

(150 ft) thick, but it thins rapidly away from the monolith 

(fig. 2) (Karner and Halvorson 1989). Talus fragments 

range from a few centimeters in diameter to large 

sections of the columns as much as 2.4 m (8 ft) in 

diameter and 7.6 m (25 ft) long (Robinson 1956). Within 

the talus sheet, three outcrops of phonolite may be 

radiating dikes (igneous intrusions shaped like a table top 

turned on edge) or part of the original uneroded igneous 

mass. 
 DETO Geologic Resource Evaluation Report 3 

Red, yellow, green, or gray sedimentary rocks compose 

the hills in the vicinity of Devils Tower (fig. 3). These 

beds of sandstone, siltstone, shale, and gypsum are about 

122 m (400 ft) thick. The oldest unit is the 

Triassic/Permian Spearfish Formation (fig. 4). The 

Spearfish Formation is overlain by Jurassic strata. 

Although no Cretaceous or Tertiary sedimentary rocks 

are exposed in Devils Tower National Monument, 

Cretaceous strata and the Oligocene White River 

Formation are present in the Missouri Buttes, smaller 

bodies of columnar-jointed igneous rock exposed 

northwest of Devils Tower (fig. 5) (Robinson 1956; 

Karner and Halvorson 1989). 

On a regional scale, the sedimentary strata present in 

Devils Tower National Monument are gently folded into 

many small rolls, basins, and domes. Faults of small 

displacement locally cut these structures. The small folds 

are superimposed on a large dome that is collapsed in the 

middle (Robinson 1956). This broad dome is defined by 

sedimentary strata that are exposed 0.8–1.6 km (0.5–1 mi) 

from the Tower and that dip gently 2°–5° away from the 

Tower. Within about 600–900 m (2,000–3,000 ft) of the 

Tower, however, the strata reflect the dome’s collapse by 

dipping 3°–5° inward to form a shallow structural basin. 

Three faults are recognized in Devils Tower National 

Monument (Robinson 1956). Two of the faults cut the 

Hulett Sandstone west of the main road and west of the 

Tower. A third fault is in the northwestern side of the 

Tower near the Tower’s base. The faults in the Hulett 

Sandstone are near vertical with displacements of less 

than 3 m (10 ft). The fault near the base of the Tower is a 

low-angle fault that trends northwesterly and dips 21° to 

the northeast. 

Devils Tower is located on the northwest flank of the 

Black Hills, an uplift formed during the CretaceousTertiary mountain-building episode called the Laramide 

Orogeny that occurred about 45–65 million years ago 

(Ma) (fig. 6). The Black Hills form a 105 by 200 km (125 

by 65 mi) elliptical dome, or doubly plunging anticline, 

that is elongated in a north–south direction (Kiver and 

Harris 1999). This forested mountain range in southwest 

South Dakota and northeastern Wyoming covers 

approximately 2 million acres. Erosion has removed the 

Paleozoic and Mesozoic strata from the central axis of 

the dome, exposing Precambrian rocks that make up the 

core of the uplift. The younger sedimentary rocks of 

Paleozoic and Mesozoic age form concentric rings 

around the Precambrian core (fig. 6). 

Park History 

The earliest maps of this region named this structure 

“Bear Lodge,” translated from the Cheyenne and Lakota 

Sioux’s “Mateo Teepee” which means “Grizzly Bear 

Lodge” (Effinger 1934). In 1875, Colonel Richard Dodge 

led a U.S. Geological Survey expedition to the Black 

Hills. His interpreters misunderstood the Native 

American’s description of the feature and translated it as 

“Bad God’s Tower.” Dodge reported it as Devils Tower 

and the name stuck. Since the tower figures strongly in 

the creation history of at least 20 Native American tribes, 

the name “Devils Tower” is offensive to many of them 

(Kiver and Harris 1999). 

Early settlers were drawn to the area and Devils Tower 

became a special place for social gatherings and 

celebrations. In 1893, local ranchers William Rogers and 

Willard Ripley climbed to the top of the tower using 76-

cm-long (30-in) stakes that they had pounded into a 

continuous crack that led to the summit. Portions of that 

stake ladder are still visible from the Tower Trail. 

In 1906, shortly after Congress passed the Antiquities 

Act, Theodore Roosevelt established Devils Tower 

National Monument. 

The first successful rock climb using mountaineering 

techniques was in 1937. In 1941, Jack Durrance led a 

group to the top to rescue George Hopkins who had 

parachuted onto the summit as a stunt (Kiver and Harris 

1999). The Durrance route remains a popular climbing 

route. 
4 NPS Geologic Resources Division 

Figure 1. Location map of Devils Tower National Monument. 
 DETO Geologic Resource Evaluation Report 5 

Figure 2. Devils Tower at Devils Tower National Monument. View to the east with the Belle Fourche River in the background. Note the 

columnar jointing and the relatively flat summit. An apron of talus, derived from the columns, extends outward from the base of the 

Tower. Photograph by Louis J. Maher, Jr., University of Wisconsin, available at http://www.geology.wisc.edu/~maher/air/air01.htm 

(access February 6, 2008). 

System Series Formation, Unit or Member Thickness in 

meters (feet) Brief description 

Quaternary Undivided Stream terrace deposits; alluvium; 

talus; landslide material 

unconformity 

Tertiary Phonolite porphyry Dark-gray to black igneous rock 

unconformity 

 Sundance Formation 

Redwater Shale Member 

12-55 

(40-180) Greenish-gray shale 

 Sundance Formation 

Lak Member 

11-20 

(35-65) 

Yellow, yellowish-brown, to pink 

calcareous sandstone & siltstone 

Jurassic Upper Sundance Formation 

Hulett Sandstone FMember 

18-27 

(60-90) Yellow, massive calc. sandstone 

Sundance Formation 

Stockade Beaver Shale Mbr 

18-24 

(60-80) 

Gray & gray-green shales with thin 

calcareous sandstones 

unconformity 

 Middle Gypsum Spring Formation 0-20 

(0-65) 

White massive gypsum with 

interbedded red mudstone 

unconformity 

Triassic/ 

Permian Spearfish Formation 183+ (600+) 

Red to maroon siltstone & sandstone 

interbedded with shale 

Figure 3. Generalized stratigraphic column for units exposed in Devils Tower National Monument from Robinson (1956) with the 

exception of the Spearfish Formation. Robinson considered the Spearfish Formation to be Triassic. However, since 1956, researchers 

have extended the Spearfish Formation into the Permian. In addition, the Lak Member of the Sundance Formation may be part of the 

Hulett Sandstone Member (Jack Epstein, USGS, written communication, January 25, 2008). 
6 NPS Geologic Resources Division 

Figure 4. Spearfish Formation in the Black Hills region. Red beds are siltstone and sandstone; white is gypsum. Photo courtesy of Dr. 

Steven Dutch, Natural and Applied Sciences, University of Wisconsin – Green Bay, available at 

http://www.uwsp.edu/geo/projects/geoweb/participants/dutch/VTrips/BHStrat.HTM (access February 4, 2008). 

Figure 5. Devils Tower at Devils Tower National Monument. View to the northwest with the Missouri Buttes in the left background. 

Missouri Buttes are smaller bodies of columnar-jointed igneous intrusions. Photograph by Louis J. Maher, Jr., University of Wisconsin, 

available at http://www.geology.wisc.edu/~maher/air/air01.htm (access February 6, 2008). 
 DETO Geologic Resource Evaluation Report 7 

Figure 6. Diagram of the Black Hills dome showing progressively younger sedimentary rock layers ringing the central Precambrian

core. Devils Tower National Monument lies within the northwest flank of the Black Hills. Modified from Strahler, 1960. 
8 NPS Geologic Resources Division 

Geologic Issues 

A Geologic Resource Evaluation scoping session was held for Devils Tower National 

Monument on June 12, 2002, to discuss geologic resources, address the status of geologic 

mapping, and assess resource management issues and needs. This section synthesizes the 

scoping results, in particular those issues that may require attention from resource 

managers. 

The geologic issues section addresses geologic issues as 

they affect the ecosystem, their importance to park 

management, and the extent to which they are 

influenced by human activities. 

Rock Climbing 

The vertical cracks and columns at Devils Tower have 

made the Monument a world-renowned site for crack 

climbing. Over 4,000 climbers visit Devils Tower each 

year, and the tower now has about 220 named routes. 

Including the famed Durrance Route, the most popular 

climbing route at the Monument, highlighted in Steve 

Roper and Allen Steck's book, 50 classic climbs in North 

America (fig. 7). By 1995, about 600 metal bolts had been 

embedded in the rock along with several hundred metal 

pitons, and activities from numerous climbers through 

the spring to fall climbing season had affected nesting 

raptors, soil, vegetation, the integrity of the rock, the 

area’s natural quiet, and the rock’s physical appearance. 

Devils Tower is also a sacred site to several Native 

American peoples of the northern plains. Some Native 

Americans complained that climbers on the sacred butte 

and the placement of bolts in the rock adversely 

impacted their traditional activities and seriously 

impaired the spiritual quality of the site. 

To address these issues, park staff developed a final 

climbing management plan (FCMP) that focuses on the 

following objectives: 

• Preserve and protect the monument’s natural and 

cultural resources for present and future generations, 

• Manage recreational climbing on the tower, 

• Increase visitor awareness of Native American beliefs 

and traditional cultural practices at Devils Tower, and 

• Provide the monument with a guide for managing 

climbing use that is consistent with NPS management 

policies and other management plans at Devils Tower 

National Monument. 

The FCMP decreased the physical impact to Devils 

Tower by eliminating the placement of new bolts or fixed 

pitons although replacement of existing bolts and fixed 

pitons is allowed. In 1995, the NPS implemented a 

voluntary June closure to climbing on Devils Tower in 

honor of the culturally significant month of June, and 

monument staff began interpreting the cultural 

significance of Devils Tower to all visitors. In the spring, 

NPS personnel identify falcon nest sites so that climbing 

routes within view of the nest site, or approximately 50 m 

(160 ft) on either side of the nest, are closed for the 

duration of the nesting season. 

Rehabilitation of access trails and summit trails helped 

repair soil and vegetation damage. The FCMP has 

significantly increased protection for natural resources 

and enhanced visitor experience by a more diverse and 

balanced interpretive program. This plan is currently 

being revised and is expected to continue the responsible 

management of climbing in the monument. 

Rockfall 

Potential rockfalls may occur from two rock units in the 

monument: the sandstone cliffs of the Hulett Member of 

the Sundance Formation and the phonolite porphyry of 

the Devils Tower (Robinson 1956). Portions of the 

Hulett sandstone cliff that surrounds the Tower may 

break off into rectangular blocks. These blocks form 

talus at the base of the cliff and locally cause large 

landslides on the hill below the cliffs (Robinson 1956). 

These blocks of sandstone range in size from a few 

inches to many feet in diameter. 

The broad apron of phonolite porphyry talus 

surrounding the Tower is a result of rockfall caused by 

failure along the fractures and joints that define the 

igneous columns. The column fragments measure from a 

few inches in diameter to as much as 2.4 m (8 ft) in 

diameter and 7.6 m (25 ft) long. 

The Monument is a popular climbing destination. The 

potential for injury from falling rocks is safety concern 

for climbers on the tower as well as visitors using the 

Tower Trail. There have been no recorded injuries from 

rockfall along the Tower Trail, and rockfall injuries to 

climbers are uncommon. The diligent promotion of 

climbing safety by the Climbing Rangers at Devils Tower 

National Monument through education and awareness 

programs deserves credit for this astounding safety 

record. 

No major rockfalls from the Tower have occurred in 

recent history. However, the Leaning Column is on the 

first pitch of the Durrance route has raised concerns. 

More than 4,000 people climb Devils Tower annually. 

The Durrance route sees a large portion of the climbing 

traffic with about 1,100 climbers ascending each year. In 

2004, a tower guide reported that the column was 

moving. In response, the U.S. Geological Survey 

conducted an analysis of the column in June 2005 (Harp 

and Lindsay 2005). 
 DETO Geologic Resource Evaluation Report 9 

According to the study, the column, at 26 feet long, has 

an estimated mass of 41 tons (82,000 pounds) (fig’s. 7–8). 

It is composed of three vertically stacked fractured 

segments. The Leaning Column is in linear contact with 

the underlying columnar pedestal, and the top edge of 

the column is in point contact with an adjacent column. 

The column contains two primary axis points at its lower 

and upper contacts. Due to the precarious nature of the 

two contact points, the stability of the column is in 

question. The column may remain in place for years or 

even hundreds of years. If new fractures are detected at 

the lower contact of the column with the pedestal, this is 

an indication of an unstable and deteriorating condition. 

It is likely that more fractures will occur to the column or 

to the one that now supports it. This will eventually lead 

to failure of the pedestal and/or toppling of the column 

(Harp and Lindsay 2005). 

Under a failure scenario, rockfall will impact the large 

flat bench at the base of the tower in the area directly 

south and west of the Tower Trail and adjacent to the 

steel viewing tubes. Any climber or hiker in the boulder 

field could be harmed by direct impact with falling rocks 

or from flying rock fragments. Failure could also lead to 

destabilization of other columns or rocks in the path of 

the event (Harp and Lindsay 2005). 

Currently, Devils Tower National Monument Climbing 

Rangers are monitoring the leaning column for signs of 

fresh phonolite rock surfaces that would indicate 

spalling failures. In addition, they have noted and are 

keeping a photo documentation record of any fractures 

or changes in the column. To better detect any new 

changes, park staff have painted the surface of the 

column. 

Mitigation of rockfall hazards generally can be dealt with 

in three ways: avoidance, stabilization, or removal. The 

simplest way to mitigate rockfall hazards is to avoid areas 

prone to rockfall. If an area is to be used, there are 

several ways that the hazard can be decreased. Rocks can 

be stabilized by bolting, cementing or in some cases 

removal of unstable rocks. Bolting and cementing are 

expensive, require periodic maintenance and seldom 

completely eliminate the hazard. Stabilization is usually 

only a short-term solution. While removal of all 

potentially unstable rocks is not possible, in some cases, 

individual rocks can be removed to eliminate an 

immediate hazard. It is crucial to assess and monitor 

potentially unstable rocks so that appropriate 

management action can be pursued. 

Redbed erosion rates 

The Permian, Triassic, and Jurassic red siltstone and 

sandstone sedimentary strata form rolling hills and 

gentle slopes because the units are poorly cemented and 

weather easily. The Administration Building and Visitor 

Center are constructed on the Redwater Shale Member 

of the Sundance Formation. Route 10 traverses several 

shale and siltstone units that are common to the 

formations in the monument. Because these units are so 

soft, the construction of new buildings and maintenance 

of existing buildings may be impacted and undercut by 

erosion because the units are so soft. 

Past erosion processes that included heavy runoff from 

hillsides caused silt to be deposited in drainage ditches, 

plugging culverts associated with the main entrance road 

(Route 10). With culverts plugged, water and debris 

flowed over the road. The preferred alternative (3) of the 

General Management Plan (NPS 2001) addresses the 

redbed erosion issue. The preferred alternative proposes 

abandonment of two of the existing culverts (plugged 

and buried in place) and redirection of runoff into a new 

paved drainage swale running along the edge of the road, 

then under the road via two new trench drains and one 

existing culvert that will be maintained in place (fig. 9). 

The project is designed to create a landform that more 

closely resembles natural conditions (Jim Cheatham, 

Chief of Resource Management, Devils Tower National 

Monument, written communication, March 30, 2006). 

Paleontology 

Paleontological resources have not been fully assessed at 

Devils Tower National Monument but are considered a 

relatively minor resource management concern (Jim 

Cheatham, Chief of Resource Management, Devils 

Tower National Monument, written communication, 

March 30, 2006). Clams, oysters, belemnites (squid), and 

other marine fossils are known from the Redwater Shale 

Member of the Sundance Formation, but no fossils have 

been found in the Spearfish or Gypsum Spring 

Formations in the monument. 

In 1997, excavation work for the new sewage disposal 

system yielded subsurface belemnites. Surface deposits 

of ammonites and belemnites are also known from three 

areas. Monument staff only casually monitor these sites, 

as the threat of theft is low (Jim Cheatham, Chief of 

Resource Management, Devils Tower National 

Monument, written communication, March 30, 2006). 

The best exposures of the Redwater Shale Member in the 

area are on Fossil Hill, northwest of the monument 

(Robinson 1956). 

Gypsum karst 

Although currently not an issue at Devils Tower National 

Monument, gypsum karst presents geological and 

engineering problems in the Black Hills. Gypsum is 

found in four stratigraphic units in the Black Hills of 

South Dakota and Wyoming: the Pennsylvanian/ 

Permian Minnelusa Formation, the Permian/Triassic 

Opeche and Spearfish Formations, and the Jurassic 

Gypsum Spring Formation. Of these, the Spearfish 

Formation and the Gypsum Spring Formation are 

exposed in Devils Tower National Monument. 

In South Dakota, dissolution of gypsum in the Spearfish 

and Gypsum Spring Formations has resulted in collapse 

and formation of many sinkholes in several areas that are 

presently undergoing urban development (Davis and 

Beaver 2002; Epstein 2002, 2003). Evidence of 

subsidence includes sinkholes over 18 m (60 ft) deep that 

have opened up over the last several decades, collapse in 

water wells and natural springs, and fresh circular scarps 

surrounding shallow depressions. As development 

increases in the Black Hills, it may be beneficial to 

consider processes involved in the formation of gypsum 

karst as part of land-use planning. 
10 NPS Geologic Resources Division 

Figure 7. Devils Tower National Monument Climbing Rangers ascend the leaning column on the classic Durrance Climbing route. 

Photograph by NPS Geologist Deanna Greco (2008). 
 DETO Geologic Resource Evaluation Report 11 

Figure8. Devils Tower as viewed from the north. Note the position of the leaning column half way up in the center of this photo. 

Photograph by NPS Geologist Deanna Greco (2008). 
12 NPS Geologic Resources Division 

 A) 

 B) 

Figure 9. Culverts along Route 10, Devils Tower National Monument. A) Culvert scheduled to be abandoned under General 

Management Plan Alternative 3, the preferred alternative. B) Culvert to be maintained in Alternative 3. Photographs courtesy of Jim 

Cheatham, Chief of Resource Management, Devils Tower National Monument. 
 DETO Geologic Resource Evaluation Report 13 

Geologic Features and Processes 

This section describes the most prominent and distinctive geologic features and processes 

in Devils Tower National Monument. 

This section provides a descriptive list of the most 

prominent and unique features and processes in the 

monument. 

Devils Tower 

Devils Tower is the reason that President Teddy 

Roosevelt established the monument. This bare mass of 

rock rises abruptly from the surrounding grasslands and 

pine forests and is one of the most conspicuous geologic 

features of the Black Hills region (fig. 10). At its base, the 

Tower is about 244 m (800 ft) in diameter. The steep 

sides rise nearly vertically for about 12–30 m (40–100 ft) 

before sloping more gently to form a narrow bench. 

Above the bench, the sides again rise steeply, at angles of 

75° to over 85°, to within about 30 m (100 ft) of the 

summit. At this point, the angle becomes less steep and 

the top edge of the Tower is somewhat rounded. In all, 

the Tower extends vertically about 183 m (600 ft) to an 

almost flat summit that measures roughly 55 m (180 ft) 

from east to west and 90 m (300 ft) from north to south 

(Robinson 1956). 

The phonolite porphyry that comprises Devils Tower 

appears light gray or brownish gray on weathered 

surfaces but fresh samples show a light- to dark-gray or 

greenish-gray very fine-grained groundmass in which 

coarser crystals of white feldspar can be seen. These 

feldspar crystals range from about 0.6–1.2 cm (0.25–0.50 

in) in diameter. 

Columnar Jointing 

The world-renowned polygonal columns are one of the 

most striking features of Devils Tower (fig. 7). In the 

middle part of the Tower, the columns are bounded by 

well-developed smooth joints, but as the columns taper 

upward, the joints between them may be wavy and some 

of the columns unite. Cross-fractures in the upper part of 

the Tower form many small irregularly shaped blocks. 

The fractures are about 120° to each other and form 4 

and 6 sided columns. The larger columns measure 1.8–

2.4 m (6–8 ft) in diameter at their base and taper 

gradually upward to about 1.2 m (4 ft) at the top. In the 

central and upper parts of Devils Tower, the columns are 

almost vertical. However, they flare out at the bench 

about 30 m (100 ft) above the base, and they are nearly 

horizontal on the southwest side. Several columns may 

join to form a larger, less distinct column that merges 

with the massive base where the columns flare out. 

Columnar joints form when shallow igneous bodies 

quickly cool. The fractures are a result of differential 

contraction during cooling because solidified rock 

requires less volume than molten rock. 

Igneous bodies cool from the surface downward and 

from the periphery inward. This process produced the 

series of joints that parallels the circumference of the 

igneous mass and the set of vertical radial cracks that are 

perpendicular to the peripheral jointing (Karner and 

Halvorson 1989; Kiver and Harris 1999). As marginal 

cooling continued, horizontal columnar joints formed 

and eventually curved upward as vertical temperature 

gradients became greater than horizontal temperature 

gradients (fig. 9). 

Origin of Devils Tower 

The origin of the magma and the original shape of the 

igneous body now called Devils Tower has been a source 

of debate since geologists examined the structure in 

1875. Carpenter (1888) originally proposed that Devils 

Tower was a volcanic-neck remnant, part of an ancient 

volcano that remained filled with magma following an 

eruption. He proposed that the magma cooled and 

contracted to form the columnar jointing seen today. 

The volcanic-neck hypothesis is still favored by many 

geologists (Dutton and Schwartz 1936; Halvorson 1980; 

Karner and Halvorson 1987). 

Because phonolite porphyry fragments are so extensively 

strewn about on and in stream terrace deposits, other 

geologists believe that Devils Tower and Missouri Buttes, 

a mass of phonolite about 6.4 km (4 mi) northwest of 

Devils Tower, are remnants of a laccolith or sill (Jagger 

1901; Darton 1909). The vent of this laccolith is thought 

to be under either Missouri Buttes (Jagger 1901) or 

Devils Tower (Darton 1909). 

Robinson (1956) proposed that Devils Tower is an 

intrusive igneous body, such as a small pluton, and not 

the remnant of a volcano. He thinks that the Tower was 

never much larger in diameter than its present base, and 

that it is connected to a sill or laccolith type body at a 

depth of 300+ m (1,000+ ft). He based this hypothesis on 

the following observations: 

• Recent erosion has exposed the present Tower. When 

intruded, it was surrounded and probably covered by 

several hundred feet of sedimentary rock. 

• The mineral composition and texture are more typical 

of shallow igneous rocks formed at depth than 

extrusive rocks. 

• No evidence of extrusive igneous activity has been 

found in the surrounding area. 

• Missouri Buttes and Devils Tower have the same 

composition so they probably were derived from a 

common magma, possibly the magma of a large 

intrusive body, such as a laccolith or sill. 

• A well drilled about 2.4 km (1.5 mi) southwest of 

Missouri Buttes encountered rock similar to both 
14 NPS Geologic Resources Division 

Devils Tower and Missouri Buttes at about 430 m 

(1400 ft) below the base of Missouri Buttes. The rock 

in the drill hole probably represents an intrusive body, 

rather than the Precambrian basement, because the 

thickness of the sedimentary rocks in this area is 

normally much greater than this depth. 

• The amount of talus, slope wash, or terrace gravel 

derived from Devils Tower and Missouri Buttes is 

relatively small, suggesting that the igneous bodies 

have not been extensively eroded. Therefore, the 

original igneous bodies were not much larger than 

what is presently exposed. 

• Columnar jointing is common in igneous bodies 

intruded at relatively shallow depths. 

• Both Devils Tower and Missouri Buttes lie in shallow 

structural depressions. 

A fourth hypothesis suggests that the depression formed 

when rising magma encountered groundwater near 

Earth’s surface, producing an explosion crater that later 

filled with lava or hot pyroclastic material that welded 

together, cooled, and contracted into columnar-jointed 

rock (Kiver and Harris 1999). This hypothesis suggests 

that Devils Tower had a very violent past and that 

erosion has removed most of the basin fill material. Only 

the thickest part of the igneous fill remains in the 

structure called Devils Tower. 

Vertical columns form where heat is lost mostly to the 

atmosphere, or to the rock surface above or a flat surface 

below. More horizontal or inclined columns tend to 

form where heat is mostly lost to the surrounding vent or 

basin walls. Either a volcanic neck, shallow intrusion, or 

a sloping basin surface could account for the nearly 

vertical columns in the center of Devils Tower and the 

outward flaring columns elsewhere around the base. 

Thus, researchers continue to debate which hypothesis is 

correct. 

While all of the origin hypotheses explain most of the 

observed features, no hypothesis explains all of the 

observed geologic data. No evidence of extrusive rock or 

phonolite debris occurs in the nearby White River 

sediments that were deposited in the Oligocene only a 

few million years after the Devils Tower rock 

crystallized, yet the vertical columns flaring outward at 

the base are similar to the columnar-jointing patterns 

that occur in known volcanic necks (Robinson 1998; 

Kiver and Harris 1999). The large crystals of feldspar in 

the phonolite suggest a slower rate of cooling that would 

occur with slightly deeper burial rather than the rapid 

cooling associated with a lava- or pyroclastic-debrisfilled explosion crater at Earth’s surface. 

However Devils Tower formed, erosion by the Belle 

Fourche River and its tributaries, combined with masswasting weathering processes such as landslides, account 

for much of the topographic expression of the tower. 

The total thickness of Mesozoic strata that covered the 

Jurassic Redwater Shale Member of the Sundance 

Formation, the youngest sedimentary unit exposed in the 

monument, prior to the emplacement of the Tower is 

unknown, but the average total thickness of the overlying 

units is 504 m (1,652 ft). Erosion rates would have been 

variable, with faster rates of erosion occurring in the 

shales and less resistant strata of the Cretaceous-aged 

Bell Fourche Shale, Mowry Shale, and Skull Creek Shale 

and the Upper Jurassic Morrison Formation. More 

deeply weathered rock is exposed in the upper 45 m (150 

ft) of Devils Tower than in the lower section, suggesting a 

longer exposure to weathering processes (Kiver and 

Harris 1999). Erosion may have slowed as resistant 

sandstones in the Cretaceous-aged Newcastle Sandstone 

and Fall River Formation were slowly removed. Wetter 

climates in the Pleistocene (Ice Age) also may have 

resulted in more frequent flood-swollen streams that 

contributed to periods of more intense erosion. 
 DETO Geologic Resource Evaluation Report 15 

Figure 10. Devils Tower. Note the flat summit, vertical columnar jointing, and curved columns at the base of the Tower. Photograph from 

Harp and Lindsay (2005). 
16 NPS Geologic Resources Division 

Map Unit Properties 

This section identifies characteristics of map units that appear on the Geologic Resource 

Evaluation digital geologic map of Devils Tower National Monument. The 

accompanying table is highly generalized and is provided for background purposes only. 

Ground-disturbing activities should not be permitted or denied on the basis of 

information in this table. 

Geologic maps facilitate an understanding of Earth, its 

processes, and the geologic history responsible for its 

formation. Hence, the geologic map for Devils Tower 

National Monument informed the “Geologic History,” 

“Geologic Features and Processes,” and “Geologic 

Issues” sections of this report. Geologic maps are 

essentially two-dimensional representations of complex 

three-dimensional relationships. The various colors on 

geologic maps represent rocks and unconsolidated 

deposits. Bold lines that cross and separate the color 

patterns mark structural features such as faults and folds. 

Point symbols indicate features such as dipping strata, 

sample localities, mine features, wells, and cave openings. 

Incorporation of geologic data into a geographic 

information system (GIS) increases the utility of geologic 

maps and clarifies spatial relationships to other natural 

resources and anthropogenic features. Geologic maps 

are indicators of water resources because they show 

which rock units are potential aquifers and are useful for 

finding seeps and springs. Geologic maps do not show 

soil types and are not soil maps, but they do show parent 

material, a key factor in soil formation. Furthermore, 

resource managers have used geologic maps to make 

correlations between geology and biology; for instance, 

geologic maps have served as tools for locating 

threatened and endangered plant species. 

Although geologic maps do not show where future 

earthquakes will occur, the presence of a fault indicates 

past movement and possible future seismic activity. 

Geologic maps will not show where the next landslide, 

rockfall, or volcanic eruption will occur, but mapped 

deposits show areas that have been susceptible to such 

geologic hazards. Geologic maps do not show 

archaeological or cultural resources, but past peoples 

may have inhabited or been influenced by various 

geomorphic features that are shown on geologic maps: 

alluvial terraces may preserve artifacts, and inhabited 

alcoves may occur at the contact between two rock units. 

Geologic features and processes often occur in or can be 

restricted to a particular stratigraphic unit (group, 

formation, or member). For example, the Hulett 

Sandstone Member of the Sundance Formation forms a 

cliff that nearly encircles Devils Tower and the Gypsum 

Spring Formation is known for beds of massive white 

gypsum. 

The features and properties of the geologic units in the 

following table correspond to the accompanying digital 

geologic data. Map units are listed from youngest to 

oldest. Please refer to the geologic time scale (fig. 11) for 

the age associated with each time period. This table 

highlights characteristics of map units such as 

susceptibility to hazards; the occurrence of fossils, 

cultural resources, mineral resources, and caves; and the 

suitability as habitat or for recreational use. Not all of the 

map units in this table are present in Devils Tower 

National Monument. The following are source data for 

the GRE digital geologic map: 

Robinson, C. S. 1956. Geologic Map of Devils Tower 

National Monument, Wyoming. Scale 1:48,000. U.S. 

Geological Survey Bulletin 1021-I. Reston, VA: U.S. 

Geological Survey. 

Izett, Glen A. 1963. Geologic Map of the Storm Hill 

Quadrangle, Wyoming. Scale 1:24,000. U.S. Geological 

Survey. Miscellaneous Geologic Investigations Map I372. Reston, VA: U.S. Geological Survey. 

Mapel, W.J., C.S. Robinson, and P.K. Theobald. 1959. 

Geologic and structure contour map of the northern and 

western flanks of the Black Hills, Wyoming, Montana, 

and South Dakota. Scale 1:96,000. U.S. Geological 

Survey Oil and Gas Investigations Map OM-191. 

Reston, VA: U.S. Geological Survey. 

Using ESRI ArcGIS software, the Geologic Resource 

Evaluation team created a digital geologic map from 

these sources. GRE digital geologic-GIS map products 

include data in ESRI shapefile and coverage GIS formats, 

FGDC metadata, a Windows HelpFile that contains all of 

the ancillary map information and graphics, and an ESRI 

ArcMap map document file that easily displays the map 

with appropriate symbology. 

GRE digital geologic data are included on the attached 

CD and are available through the NPS Data Store 

(http://science.nature.nps.gov/nrdata/). 
Map Unit Properties Table Age Map Unit (symbol) Unit Description Topographic Expression Erosion Resistance Paleontological Resources Min

Res

QUATERNARY Unconsolidated material (Qta, Qal, Qt, Ql, Qlp, Qls) 

Qta: stream terrace deposits & alluvium, undifferentiated. Gravel, sand, silt, & mud. Stream deposits 

(alluvium) found in valleys of small streams around the Tower & in the valley of the Belle Fourche R., that cuts across the monument’s SE corner. NE of the Belle Fourche R., between the river & the main road, is terrace cut into the Spearfish Fm. Qal: alluvium – sand, silt, & gravel 

Qt: terrace alluvium – sand, silt, & gravel 

Ql: talus & landslide material 

Qlp: talus & landslide material, chiefly phonolite 

Qls: talus & landslide material, chiefly Hulett Sandstone 

Terraces & flood plains; talus slopes 

Alluvium: low; Talus: high None San

Gra

White River Formation (Twr) 

Light-gray & light brown medium- to coarse-grained friable sandstone & conglomeratic sandstone; 

locally contains calcium carbonate cement. Locally thick bedded; unconformable lower contact. Thickness averages 9 m (30 ft), range 0-15 m (0-50 ft). 

Forms slopes & some ragged ledges in area 

Not exposed in Devils Tower NM 

Early Oligocene brontothere tooth fragment found in gravel pit N of Devils Tower (NW1⁄4 sec. 27, T55N, R65W) 

Not in DTow

Unconformity 

TERTIARY 

Phonolite porphyry (Tp) 

Conspicuous crystals of white feldspar in light- to dark-gray or greenish-gray very fine-grained groundmass. Feldspar commonly about 0.6-1.2 cm (0.25-0.5 in) in diameter. Weathers to light gray or brownish gray. Under the microscope, the feldspar is crudely zoned, untwined, & altered alkali feldspar 

(anorthoclase). Smaller dark-green pyroxene crystals are clinopyroxene, either aegerite or aegeriteaugite. Similar in composition to the igneous rocks at Missouri Buttes. 

Devils Tower High None 

Feld(ano) 

Regional Unconformity 

Belle Fourche Shale (Kb) 

Dark-gray to black shale with numerous dark purplish-red weathering siderite concretions in lower part, & several beds of light-gray- & yellow-weathering limestone concretions in middle & upper parts; several beds of bentonite (altered volcanic ash). Not exposed in Devils Tower NM. Thickness: 210-240 m (700-800 ft) 

Not exposed in Devils Tower NM 

Low Not exposed in Devils Tower NM Side

Ben

Mowry Shale (Km) 

Dark-gray siliceous shale, weathers light gray; many thin bentonite beds. Thickness: 61-76 m (200-250 

ft). Not exposed in Devils Tower NM. 

Not exposed in Devils Tower NM 

Low; Not in Devils Tower NM 

Numerous fish scales along shale partings 

Not in DTow

Newcastle Sandstone (Knc) 

Discontinuous beds of light-gray sandstone siltstone & dark-gray carbonaceous shale or claystone; a 

few beds of impure lignite & bentonite. Gradational lower contact. Thin to thick bedded; ripple marks; low-angle cross stratification. Thickness varies within short distances, but averages 11-12 m (35-40 ft). 

Not exposed in Devils Tower NM. 

Forms slopes with some prominent ledges 

Higher than shale; lower than phonolite 

Not exposed in Devils Tower NM 

Not in DTow

Skull Creek Shale (Ksc) 

Slightly silty black greasy shale with a few ferruginous siltstone, siderite, & cone-in-cone concretions; 

fissile to subfissile. Gradational lower contact. Thinly laminated. Thickness averages 76 m (250 ft). Not 

exposed in Devils Tower NM. 

Forms gentle slopes Low 

Fragmentary plesiosaur bones found in lower part of formation 

Not in DTow

Fall River Formation (Kr) 

Gray to light-brown very fine grained thin- to thick-bedded sandstone with a few gray to light-brown silty claystone & clayey siltstone beds in upper part; gray to light-brown thinly laminated carbonaceous clayey siltstone & silty claystone layered with very fine to fine-grained sandstone in lower part. Unconformable lower contact. Thin to thick bedded; even bedded, locally lenticular, ripple marks; lowangle cross-stratification; sandstone bars & channel-fill deposits. Thickness avg 40 m (130 ft), range 37-

44 m (120-145 ft). Not exposed in Devils Tower NM. 

Forms ledges & cliffs separated by moderately steep slopes 

Relatively high Trails & tubes of soft- bodied organisms Not 

in DTow

Unconformity 

LOWER 

CRETACEOUS

Lakota Formation (Kl) 

Variegated sandy claystone & clayey sandstone, gray dense siltstone, lenticular gray to light-brown 

sandstone & conglomeratic sandstone; contains highly polished pebbles of varicolored chert, red & white quartzite, & white quartz. Unconformable lower contact, but locally gradational. No apparent fractures or joints. Thin- to thick-bedded, locally massive; rare ripple marks; low- to high-angle, medium-scale tabular & lenticular cross-stratification; lenticular sandstones common. Thickness avg 55 

m (180 ft), range 35-79 m (115-260 ft). Not exposed in Devils Tower NM. 

Forms moderately steep slopes with a few ledges and cliffs 

Relatively high 

Marine invertebrate fossil debris in polished pebbles & cobbles (Psaronius of Pennsylvanian or Permian age; Favositessp. of Late Ordovician to Devonian age) 

Uramin

Regional Unconformity 
Age Map Unit (symbol) Unit Description Topographic Expression Erosion Resistance Paleontological Resources Min

Res

Fuson& Lakota, Formations, undifferentiated (KJu) 

Light yellowish-gray to white fine- to coarse-grained sandstone & conglomeratic sandstone, irregularly layered with red, green, yellow, gray, & black claystone; thickness variable within short distances. Thickness: 18-67 m (60-220 ft). Not exposed in Devils Tower NM. 

Not exposed in Devils Tower NM 

Not exposed in Devils Tower NM 

Not exposed in Devils Tower NM Coa

Morrison Formation (Jm) 

Green, greenish gray, & grayish-red structureless limy claystone & slightly sandy claystone with a few thin discontinuous light-gray limestone & sandstone beds; locally consists entirely of light-gray very fine-grained sandstone that weathers to rounded knobs. Gradational lower contact. No apparent fractures or joints. Thin- to thick-bedded sandstone, lenticular & massive, rare ripple marks; low-angle medium-scale lenticular cross-stratification. Thickness avgs 24 m (80 ft), range 0-30 m (0-100 ft). Not exposed in Devils Tower NM. 

Weathers to rounded knobs & grass-covered slopes 

Relatively low 

Locally contains ostracodes, gastropods, & vertebrate remains 

Not in DTow

Sundance Fm.: Redwater Shale Member (Jsr) 

Greenish-gray shale with thin discontinuous fossiliferous sandy limestone & limy siltstone beds in upper part; topmost bed is orange-brown limy siltstone. Gradational lower contact. No apparent fractures or joints. Thin-bedded limestone; ripple marks common in topmost sandstone beds. Thickness avg 52 m (170 ft), range 12-55 m (40-180 ft). Jsrls: fossiliferous limestone beds in the upper part of the Redwater Shale Member 

Forms grasscovered slopes; encircles Devils Tower; mostly covered by talus 

Low 

Fragments of marine invertebrates: ammonites, belemnites (squids), crinoid stems, & pelecypods (clams & oysters) 

Nondoc

Sundance Fm.: Lak Member (Jsl) 

Yellow to pink siltstone & very fine-grained sandstone & siltstone. Minor thin gray-green sandy shale partings. Poorly cemented. Gradational lower contact. No apparent fractures or joints. Thin-bedded sandstone in lower part. Thickness averages 14 m (45 ft), range 11-20 m (35-65 ft). 

Weathers to gentle slopes covered with vegetation 

Soft sandstone & siltstone None documented Non

doc

Sundance Fm.: Hulett Sandstone Member (Jsh) 

Yellowish-brown very fine-grained glauconitic calcareous sandstone. Gradational lower & upper contacts. Sandstone in lower 1.5-3 m (5-10 ft) in beds from less than 2.54 cm-0.6 m (1 in-2 ft) thick separated by shale partings less than 2.54 cm-15 cm (1-6 in) thick; ripple marks. Middle part of mbr has massive sandstone beds 1.5-6 m (5-20 ft) thick. Upper 1.5-3 m (5-10 ft) is thin bedded, locally shale, & poorly cemented. Thickness averages 24 m (80 ft), range 18-27 m (60-90 ft). 

Forms massive near-vertical, well-cemented cliff 

High; resistant to weathering None documented Non

doc

Sundance Fm.: Stockade Beaver Shale Member (Jssb) 

Thin sandstone at base contains black or dark-gray water-worn chert pebbles with a maximum dimension of about 5 cm (2 in). Above basal sand, lower half of mbr is mostly gray-green shale. Upper half is dark-gray to gray-green shale with interbedded fine-grained calcareous sandstone ranging from less than 0.3-1.8 m (1-6 ft) thick. Unconformable lower contact; gradational upper contact. No apparent fractures or joints. Thin-bedded; a few ripple marks. Thickness averages 21 m (70 ft), range 18-24 m (60-80 ft). 

Poor to fair exposures; forms slopes 

Low None documented Non

doc

UPPER 

JURASSIC 

Sundance & Gypsum Spring Formations, undifferentiated (Jsg) 

(see individual units) Regional (J-2) Unconformity 

MIDDLE 

JURASSIC Gypsum Spring Formation (Jgs) White massive gypsum interbedded with red gypsiferous claystone & siltstone; a few beds of gray cherty limestone & dolomite near top of formation. Laminated to thin bedded. Unconformable lower contact. Thickness averages 5-11 m (15 to 35 ft) Good exposures; forms bare slopes Low None documented Gyp

Regional (J-1) Unconformity 

TRIASSIC PERMIAN Spearfish Formation* (TRPs) Red clayey siltstone, siltstone, & sandstone with red sandy shale; beds of massive white gypsum in lower half; lower part not exposed. Poorly cemented. Thin to thick-bedded. Some joints in sandstone beds. Base not exposed. Uppermost 30 m (100 ft) exposed in Devils Tower NM. Good exposures; forms bare slopes or conspicuous brownish-red to maroon cliffs Low; weathers very easily None found in Devils Tower but fossils of Triassic land vertebrates found in Wyoming Gyp

Robinson, Charles S. 1956. Geology of Devils Tower National Monument, Wyoming. Bulletin 1021-I. Denver, CO: U.S. Geological Survey. * Robinson considered the Spearfish Formation to be a Triassic unit. Since 1956, the Spearfish Formation has been found to extend into the Permian. 
 DETO Geologic Resource Evaluation Report 19 

Geologic History 

This section describes the rocks and unconsolidated deposits that appear on the digital 

geologic map of Devils Tower National Monument, the environments in which those 

units were deposited, and the timing of geologic events that created the present 

landscape. 

This section provides a more detailed description of the 

structure, tectonics, depositional and erosional history, 

and general stratigraphy of Devils Tower National 

Monument and the surrounding area. The Devils Tower 

and Black Hills region records a long and complex 

geologic history. At one time, Precambrian sediments 

that now compose the core of the Black Hills were 

buried about 14 km (9 mi) beneath the surface by 

Paleozoic, Mesozoic, and Cenozoic sediments. Intense 

heat and pressure at depth metamorphosed the 

Precambrian sediments and magma engulfed and 

injected itself into the rock. The metamorphosed and 

igneous rock units were uplifted during the Laramide 

Orogeny and erosion then exposed today’s oval-shaped 

Black Hills (fig. 6). Cored by Precambrian rocks, the 

Black Hills are rimmed by Paleozoic and Mesozoic 

sedimentary strata. Devils Tower National Monument 

lies within the Black Hills region and is an erosional 

remnant of igneous activity generated during the 

Laramide Orogeny. 

Precambrian History of the Black Hills Region 

The Precambrian rocks exposed in the Black Hills are 

predominantly Early Proterozoic metasedimentary units 

(sedimentary rocks that have undergone metamorphism) 

that were deposited about 1,600–2,500 million years ago 

(Ma) (fig. 11). Understanding both the depositional and 

tectonic evolution of the Black Hills during the 

Precambrian is limited due to the complex geology and 

lack of precise age control for the metasedimentary rocks 

of the Black Hills. While age dates are available for 

igneous rocks in the Black Hills, precise ages for the 

metasedimentary rocks are lacking. 

Correlations with units in surrounding areas are 

hampered by the fact that the Black Hills are more than 

300 km (190 mi) from Precambrian outcrops in southern 

Wyoming and more than 1,100 km (680 mi) away from 

similar age rocks in Manitoba and Saskatchewan. 

Stratigraphic, depositional, tectonic, and chronologic 

studies on the Black Hills have resulted in the following 

general interpretations (Redden et al. 1990). 

The Black Hills are underlain by Archean basement 

rocks about 2,500 million years old that belong to the 

Wyoming Archean Province (fig. 12). At the time these 

rocks were emplaced, Wyoming formed the southern 

margin of the landmass that would form the core of the 

North American craton. Prior to 2,170 Ma, an 

extensional (pull-apart) tectonic setting developed along 

the passive tectonic margin of the Wyoming Archean 

Province. Coarse-grained clastic rocks with local 

anomalous concentrations of uranium and minor 

chromite were deposited from west-to-east in alluvial 

fans forming on continental Archean basement. 

Between 1,980 Ma and 2,170 Ma, the extensional 

tectonic setting along the plate margin changed to one of 

compression (fig. 13). Gabbro sills (a type of intrusive 

igneous rock) intruded the Early Proterozoic strata and 

Archean basement about 2,170 Ma. Deformation caused 

folding about north-northwest trending axes. The 

deformation may record early activity in the 

development of the collision zone between the Wyoming 

Archean Province and the Trans-Hudson Province. 

Alluvial fans of quartz-rich, feldspathic sediment derived 

from the east bordered tidal flat and marine shelf 

environments to the west and south. 

Black shale was deposited in a deepening basin in the 

Black Hills region about 2,000 Ma. This deposition was 

accompanied by the submarine eruption of basalt. Deepwater deposition by density currents (turbidites) flowing 

over the continental shelf and down the continental 

slope then followed. While a marine basin formed in the 

Black Hills region, the eastern margin of the Wyoming 

Archean Province, which was located east of the current 

Black Hills, was undergoing uplift, volcanism, and 

possibly deformation. Water depths increased from east 

to west and north to south. 

A 90-million year time gap separates the turbidite 

deposits and basalt flows of the basin from overlying 

conglomerates, debris flows, and minor volcanic rocks. 

In some areas, the older rocks were folded and 

overturned by a deformational event that occurred prior 

to deposition of the younger sediments. The deformation 

is poorly understood, but the general northerly trend of 

the folds suggests another episode of east-west tectonic 

closure. Although speculative, the deformation may be 

attributed to plate margin effects along the TransHudson and Wyoming Archean Province boundary. 

A thick, widespread shale unit exposed in the central 

Black Hills was deposited between 1,710 and 1,880 Ma. 

The general lack of shallow-water structures suggests 

that the main basin in the current Black Hills region 

continued to evolve as an intracontinental or back-arc 

basin (fig. 13) from about 1,900–1,800 Ma. 

All the stratified rocks and the Archean basement were 

folded along east-northeast axes sometime between 

about 1,710 and 1,850 Ma. After this folding event, but 

before 1,710 Ma, the stratified rocks and Archean 

basement were again folded along north-northwest axes 

and regionally metamorphosed. Rb-Sr age dates suggest 

that the metamorphism may have occurred about 1,840 
20 NPS Geologic Resources Division 

Ma. The compressional events probably were associated 

with convergence of the Wyoming Archean Province 

with the Trans-Hudson Province. 

The Harney Peak Granite, into which Mount Rushmore 

was carved, probably formed by melting of Archean crust 

and minor amounts of Early Proterozoic rocks about 

1,710 Ma. Too young to be related to the Trans-Hudson 

deformation event that took place about 1,840–1,910 Ma, 

the Harney Peak Granite may be related to tectonic 

activity in the Central Plains Province to the south (fig. 

12). 

Paleozoic History of the Black Hills Region 

Although only 6% of Earth’s history is recorded in the 

Paleozoic Era (251–542 Ma) compared to the roughly 

88% of Earth history represented by the Precambrian 

(542–4,600 Ma), the Paleozoic is comparatively rich in 

detail because of fossils. The Paleozoic strata that rim the 

core of the Black Hills, and the fossils they contain, 

record several episodes of marine deposition followed by 

subaerial erosion. 

Cambrian and Ordovician sandstone, glauconitic shale, 

limestone, and dolomite were deposited in marine 

environments although the shoreline did not reach 

Wyoming until Middle Cambrian time (Boyd 1993; 

Driscoll et al. 2002). Sea level rose in the latest Cambrian 

and flooded almost the entire North American 

continent, leaving a strip of land or a series of islands 

exposed along what is known as the Transcontinental 

Arch, an upland that stretched from northern Minnesota 

southwestward across South Dakota, northwestern 

Nebraska, Colorado and northwestern New Mexico (fig. 

14). Before the end of the Early Ordovician, the sea 

regressed off the craton and erosion stripped much of 

the Cambrian and Ordovician strata from the area during 

the Devonian. Silurian age rocks are not present in the 

Black Hills. They may have been eroded during the 

Devonian or were never deposited. 

During Middle Devonian to Middle Mississippian time, 

the western margin of North America was undergoing 

compression as the North American lithospheric plate 

collided with the Pacific Plate, causing the Antler 

Orogeny (fig. 11). This collision caused a series of 

Devonian transgressions during which the shoreline 

advanced from west to east onto the craton, depositing 

marine sediments throughout the northern and western 

part of Wyoming (Boyd 1993). In the Late Devonian to 

Early Mississippian, a major regression was followed by 

yet another west to east transgression (fig. 15). 

In some cratonic basins such as the Williston Basin in 

North Dakota and Montana (fig. 14), the black marine 

shale of the Devonian Bakken Formation is a prolific 

petroleum source rock. In the Black Hills, the 

widespread Mississippian-age Madison, or Pahasapa, 

Limestone was deposited in a warm, shallow-water 

environment. When the sea regressed in the Late 

Mississippian, elaborate karst (solution) features 

developed in the Madison Limestone, including those 

seen at Wind Cave National Park and Jewel Cave 

National Monument in South Dakota. Today, the 

Madison Limestone is a major aquifer in the Black Hills 

region. 

At the end of the Paleozoic, the major landmasses were 

coming together to form a supercontinent called 

Pangaea. Wyoming was located along the western margin 

of Pangaea. The South American landmass collided with 

the southern margin of North America, generating the 

forces responsible for the Ancestral Rockies in Colorado. 

In general, the Pennsylvanian and Permian strata in 

Wyoming record episodic transgressive and regressive 

cycles (Boyd 1993). Terrestrial redbeds are interlayered 

with marine carbonates, sandstone, and phosphatic and 

cherty strata. 

By the end of Middle Permian time, the shoreline had 

shifted to the west and near-shore, shallow marine 

clastics of the lower Spearfish Formation were deposited 

in the Black Hills and Devils Tower region (Sabel 1981, 

1984). Bedded gypsum, salt casts in rippled siltstone, and 

micritic limestone and dolomite suggest subaqueous, 

hypersaline environments of deposition for the lower 

Spearfish. Stromatolites and oscillation ripples indicate 

periods of shallow marine conditions. At the end of the 

Permian, this area was located approximately 30° north 

latitude. Today, a similar hot arid climate and 

depositional environment is found in the marginal 

marine sabkhas (salt flats) of the Persian Gulf region. 

Mesozoic History of the Black Hills Region 

Triassic Period 

By the Early Triassic, the major landmasses had come 

together to form Pangaea (fig. 16). An Early Triassic sea 

flooded eastward and transgressed quickly over the 

gently westward sloping central Wyoming shelf (Picard 

1993; Dubiel 1994). The Early Triassic part of the 

Spearfish Formation represents a low gradient, coastal 

plain environment located east of this advancing sea 

(Robinson 1956; Sabel 1981, 1984; Picard 1993). 

Intermittent fluvial systems developed along with 

isolated bodies of water. High evaporation rates 

encouraged the growth of algal mats. Dolomites, 

limestones, and sulfates precipitated in these bodies of 

water, which were recharged by runoff and saline 

groundwater. 

Jurassic Period 

By the end of the Triassic, Pangaea was breaking apart 

and the landmasses began migrating to their current 

positions. A period of uplift and erosion occurred 

following the deposition of the Spearfish Formation. A 

shallow epicontinental seaway inundated large portions 

of the Western Interior of North America, a 

physiographic province bordered to the west by a rising 

mountain range caused by the Sevier Orogeny and to the 

east by the stable North American craton (Brenner 1983; 

Kvale et al. 2001). The Ancestral Rocky Mountains 

separated this seaway from the Gulf of Mexico, and in 

some areas, the seaway may have been less than 500 km 

(300 mi) wide. 

Tectonism caused global eustatic sea level fluctuations so 

that this shallow seaway spread southward from the 
 DETO Geologic Resource Evaluation Report 21 

Arctic to inundate the Western Interior in a series of 

transgressive-regressive sequences that are 

stratigraphically packaged between unconformities 

(Pipiringos and O’Sullivan 1978; Brenner and Peterson 

1994; Peterson 1994; Kvale et al. 2001). At this time, 

Wyoming lay within 15°–20° North latitude, and the 

abundance of red beds, evaporites, and shallow water 

carbonates suggest that Jurassic paleoclimate in the 

Devils Tower National Monument region was generally 

warm and dry (Saleeby and Busby-Spera 1992; Kvale et 

al. 2001). 

In the Early Jurassic, the inland sea transgressed from the 

north to inundate western Montana and the Williston 

Basin area of Montana and North Dakota (Brenner and 

Peterson 1994; Peterson 1994). Vast ergs (eolian sand 

seas) developed south of the epicontinental seaway in 

Utah, Colorado, New Mexico, and Arizona. Early 

Jurassic deposits are not represented in the Devils Tower 

region. 

The Middle Jurassic Gypsum Spring Formation 

represents a return of the sea into the area following an 

Early Jurassic shoreline regression and records the first 

of two Middle Jurassic transgressive-regressive 

depositional cycles (Brenner and Peterson 1994; 

Peterson 1994; Kvale et al. 2001). The depocenter of the 

Middle Jurassic inland sea was located in central Utah 

and westernmost Wyoming (fig. 17). East of the 

depocenter, the average depth of the shallow sea was less 

than 100 m (300 ft). 

Thicker in western Wyoming, the Gypsum Spring 

Formation thins to the east and southeast (Picard 1993). 

In central Wyoming and the Big Horn Basin in northcentral Wyoming, the Gypsum Spring Formation has 

been divided into a lower unit consisting of interbedded 

evaporites and siltstones deposited in a sabkha type 

environment that was periodically flooded; a middle unit 

of interbedded limestones and dolomites that were 

deposited in a shallow, warm water subtidal 

environment; and an upper unit of nodular and 

interbedded evaporites and siltstones deposited in 

another sabkha type environment (Picard 1993, 1997; 

Guyer 2000). The thick gypsum and anhydrite masses of 

the lower unit are predominantly microcrystalline 

(Williams and Parcell 2003). The middle unit contains 

several species of ammonites, pelecypods, and crinoids. 

Extensive reefs developed in many parts of the globe 

during the Jurassic and Middle Jurassic. Microbial 

buildups have been recognized in the Gypsum Spring 

Formation in the Big Horn Basin. These reefs record 

some of the earliest known occurrence of Jurassic 

microbial reefs in North America (Parcell and Williams 

2003; Ploynoi and Parcell 2005). The buildups are 

composed of blue-green algae (cyanobacteria), coralline 

red algae, green algae, encrusting foraminifera, 

encrusting bryozoa, sponges, corals, and mollusks. The 

buildups probably developed in shallow, possibly 

brackish water less than 1 m (3 ft) deep. 

The contact between the Gypsum Spring Formation and 

underlying strata is one of the most prominent 

unconformities in the Paleozoic and Mesozoic record of 

Montana, Wyoming, and Utah (Picard 1993; Peterson 

1994; Schmude 1999). Today, the Gypsum Spring 

evaporites serve as caprocks (top seals) over Nugget 

Sandstone petroleum reservoirs in Wyoming and Utah 

(Picard 1993). 

The shale, glauconitic sandstone, and limestone 

sequences of the Sundance Formation in the Black Hills 

record at least two transgressive-regressive cycles, 

including the last and most extensive transgression of the 

Jurassic age, which covered much of the Western 

Interior (Brenner 1983; Picard 1993; Kvale et al. 2001). 

The Stockade Beaver Shale, Hulett Sandstone, and Lak 

Members comprise the lower Sundance Formation and 

record a Middle Jurassic transgressive-regressive 

depositional cycle (Brenner and Peterson 1994; Peterson 

1994). The marine Stockade Beaver Shale Member is 

overlain by the regressive marine Hulett Sandstone 

Member deposited in a variety of subenvironments of a 

barrier-island complex including shoreface and beach, 

tidal channels, and back-barrier lagoon and tidal flats 

(Picard 1993; Brenner and Peterson 1994). The lower 

Sundance Formation is capped by the red siltstones of 

the nonmarine Lak Member. 

In eastern Wyoming, the upper Sundance Formation is 

represented by the greenish-gray shales and fossiliferous 

sandy limestones of the Redwater Shale Member, an 

Upper Jurassic transgressive-regressive depositional 

cycle (Brenner and Peterson 1994; Peterson 1994). While 

previous Jurassic regressions resulted from eustatic 

(worldwide) sea level falls, regression of the shoreline at 

the top of the Redwater Shale cycle was the result of an 

increase in siliciclastic sediment supply. Erosion of 

uplifting highlands to the west, generated by increased 

tectonic activity (Sevier Orogeny) along the North 

American west coast, accelerated sedimentation rates 

and filled the Western Interior Basin faster than the basin 

could respond to the Upper Jurassic eustatic rise in sea 

level (Hallam 1988; Brenner and Peterson 1994; Peterson 

1994). 

In the Bighorn Basin, rare Middle Jurassic dinosaur 

megatrack sites have been discovered in the Gypsum 

Spring Formation and the lower Sundance Formation 

(Kvale et al. 2001). Footprints in both formations are 

preserved in intertidal to supratidal coastal environments 

that were once thought to be marine in origin. Possible 

swim tracks in the Gypsum Spring Formation also have 

been assigned to bipedal dinosaurs and crocodilians 

(Kvale et al. 2001; Mickelson et al. 2005). 

The Morrison Formation represents continental 

environments of deposition during the final retreat of the 

Jurassic seas. The Morrison Formation is a widespread 

nonmarine complex that covers most of the Western 

Interior. Lying on a scoured and channeled upper 

Sundance Formation, the Morrison attests to a change to 

terrestrial conditions. Alluvial fans, lakes, and braided 

and meandering streams are common environments in 

the Morrison (Picard 1993). The Morrison Formation is 

world renown for its dinosaur fossils and also contains 

significant uranium in fluvial sandstone deposits. 
22 NPS Geologic Resources Division 

Cretaceous Period 

Although the subduction zone was far to the west of the 

Black Hills region during the Sevier Orogeny, 

compressive forces caused by the collision were felt far 

inland. Cretaceous sedimentary rocks record deposition 

in a Western Interior foreland basin that formed, in part, 

as a flexural response to crustal loading by the fold-andthrust belt of western North America and, in part, as a 

response to subduction of the Farallon plate (Dickinson 

1974; Dickinson and Snyder 1978; Steidtmann 1993). 

As the mountains rose in the west and the roughly northsouth Western Interior Basin subsided, the Gulf of 

Mexico separating North and South America continued 

to rift open in the south, and marine water began to spill 

into the basin. At the same time, marine water began to 

transgress from the Arctic region in the north. Relative 

sea level rose and fell frequently throughout the 

Cretaceous so that Cretaceous sediments record a 

complex history of transgressive-regressive cycles. 

The Lower Cretaceous sandstones, shales, minor 

carbonates and coal of the Lakota and Fall River 

Formations represent fluvial, floodplain, and marsh 

depositional environments. The Skull Creek Shale, 

Newcastle Sandstone, Mowry Shale, and Belle Fourche 

Shale in the Black Hills region record episodic 

fluctuations of relative sea level and were deposited in 

near-shore to off-shore depositional environments as the 

seaway expanded. 

Eventually, the Upper Cretaceous seaway became the 

most extensive interior seaway ever to cover the 

continent (fig. 18). The Western Interior Seaway 

extended from today’s Gulf of Mexico to the Arctic 

Ocean, a distance of about 4,827 km (3,000 mi) 

(Kauffman 1977; Steidtmann 1993). During periods of 

maximum transgression, the width of the basin was 1,600 

km (1,000 mi). The basin was relatively unrestricted at 

either terminus. 

At the close of the Cretaceous, the Western Interior 

Seaway drained from the area of the future Black Hills 

uplift. The seas gradually receded, and a shallowingupward sequence of sedimentation developed from the 

offshore marine Pierre Shale to the near-shore marine 

Fox Hills Sandstone (exposed in Wyoming and the 

Dakotas but not in the Black Hills) and the fluvio-deltaic 

Lance Formation/Hell Creek Formation (exposed in 

Wyoming and the Dakotas but not in the Black Hills). 

The Lance and equivalent Hells Creek formations were 

deposited within the last 3 million years of the 

Cretaceous (Driscoll et al. 2002). Streams flowed 

eastward from the east side of the Powder River Basin 

located in northeastern Wyoming, west of the present 

Black Hills region. These drainage patterns indicate that 

the Black Hills uplift did not yet exist. 

Cenozoic History of the Black Hills Region 

The Laramide Orogeny and Devils Tower 

During the Late Cretaceous to Early Tertiary (75–35 Ma) 

Laramide Orogeny, thrust faults cut deeply into Earth’s 

crust, thrusting ancient plutonic and metamorphic 

basement rocks to the surface and forming the modern 

Rocky Mountains. These thrust faults have steeply 

dipping fault planes at the surface that curve and become 

nearly horizontal at depth. Eventually, they reach 

Precambrian basement crystalline rock at depths up to 9 

km (30,000 ft or 5.7 mi) below sea level (Gries, 1983; 

Erslev, 1993). In the Black Hills, ancient Precambrian 

margins involving the Wyoming Archean province and 

the Trans-Hudson province may have provided planes of 

weakness that influenced Laramide folding, faulting, and 

magmatic activity (Lisenbee and DeWitt 1993). 

The basement-cored arches of the Rocky Mountains are 

bounded by thrust faults and separated by sedimentfilled basins. The north-south trending, doubly-plunging 

Black Hills anticline is the easternmost expression of the 

Laramide Orogeny. The initial phase of uplift occurred in 

the Paleocene. With uplift, sediments were shed into the 

Powder River Basin and the Williston Basin to the north 

(fig. 19). 

Two large blocks of Precambrian basement were thrust 

upward in the Black Hills region during the Laramide 

Orogeny (Karner and Halvorson 1989). Just west of the 

Missouri Buttes lies the Black Hills monocline that forms 

the western edge of the northern block. This northern 

block may have produced deep fractures in the crust that 

provided a route for magma to reach the surface. Several 

domes in this area formed from the vertical movement of 

magma prior to the emplacement of the Missouri Buttes 

and Devils Tower. Stocks, dikes, sills, and laccoliths were 

emplaced across the northern Black Hills uplift during 

this initial tectonism (62 Ma) (Lisenbee and DeWitt 

1993). Near the end of the Eocene, magma approached 

or perhaps reached the surface. Devils Tower and 

Missouri Buttes were emplaced about 40 Ma and 50 Ma, 

respectively (Karner and Halvorson 1989). Both Devils 

Tower and Missouri Buttes lie within a depression 

formed within relatively horizontal sedimentary strata. 

With Laramide uplift, deposition ceased and erosion 

began. Most of the present surface was exposed by late 

Oligocene time (Karner and Halvorson 1989). An 

estimated 200–1,000 m (660–3,300 ft) of sedimentary 

cover was eroded from Devils Tower. 

Devils Tower 

Detailed petrology of the Devils Tower phonolite 

porphyry shows phenocrysts of anorthoclase, aegirineaugite, and sphene in a trachytic groundmass consisting 

of the minerals albite, microcline, analcime, aegirine, 

nepheline, and nosean. Calcite, zeolites, hematite, clay, 

and analcime are common alteration or replacement 

products (Robinson 1956; Karner and Halvorson 1987, 

1989). Green aegirine-augite is the principal mafic 

mineral and is found as phenocrysts and as groundmass 

needles. Analcime is one of the primary groundmass 

constituents. 

As discussed previously in the “Geologic Features and 

Processes” section, four general hypotheses have been 

proposed for the origin of Devils Tower. 

1. Devils Tower is an erosional remnant of a volcanic 

neck. In this hypothesis, the volcano vented to the 
 DETO Geologic Resource Evaluation Report 23 

surface through more than a hundred meters (several 

hundred ft) of sediments (Carpenter 1988; Dutton and 

Schwartz 1936; Halvorson 1980; Karner and 

Halvorson 1987, 1989). 

2. Devils Tower is a remnant of a laccoltih or sill (Jagger 

1901; Darton 1901). 

3. Devils Tower is an intrusive igneous body, such as a 

small pluton (Robinson 1956). 

4. Devils Tower lies in a depression that is the remnant of 

a crater formed during an explosive volcanic episode 

when rising magma encountered meteoric 

groundwater. Devils Tower is the erosional remnant of 

the lava and hot pyroclastic material that filled this 

crater (Kiver and Harris 1999). 

The nearly vertical columns in the center of Devils 

Tower and the outward flaring columns elsewhere 

around the base could have formed as part of a volcanic 

neck, shallow intrusion, or a sloping basin surface. Still, 

as explained in the aforementioned section, apparent 

discrepancies exist for all of the origin hypotheses. 

Post-Laramide History of the Black Hills Region 

A second phase of tectonic activity impacted the region 

in the latest Paleocene and Eocene, but by Late Eocene, 

the Laramide Orogeny was over and continental deposits 

of the White River Group covered the uplift. However, 

Eocene deposits fill paleo-valleys carved into the 

underlying strata, suggesting that the topographic form 

of the present Black Hills existed prior to deposition of 

these overlying sediments. 

Widespread deposition, normal faulting, regional uplift, 

climatic changes, development of modern drainage 

systems, and basin excavation all occurred during the 

Neogene (Miocene and younger) in Wyoming (Flanagan 

and Montagne 1993). Abundant volcaniclastic detritus of 

remote origin and locally derived detrital sediments filled 

the Laramide basins during the Oligocene and Miocene. 

Many basins may have contained over 915 m (3,000 ft) of 

Miocene and Pliocene rocks (Flanagan and Montagne 

1993). Erosion of the basins occurred after the 

establishment of large, through-flowing rivers in the 

Pliocene and Pleistocene. 

Extensional (pull-apart) tectonics impacted northwest 

Wyoming around 17 Ma and 13 Ma (Flanagan and 

Montagne 1993). Normal faults, coupled with younger 

faults to the east and north and the mid-Miocene change 

in sedimentation in Nebraska, suggests that the faulting 

in Wyoming was related to the tectonism affecting the 

Basin and Range, Rio Grande Rift, and Snake River Plain 

at this time. 

Regional uplift in the Black Hills and Devils Tower area 

occurred in a series of pulses. The first pulse occurred 

during the Laramide Orogeny. A second pulse occurred 

in the late Oligocene to early Miocene and caused a 

change in flow direction of some Rocky Mountain river 

systems and influenced conglomeratic sedimentation in 

Wyoming and Nebraska. The third and major pulse of 

uplift began in the mid-Miocene (about 17 Ma) and 

continued through the Pleistocene (Steidtmann et al. 

1989; Flanagan and Montagne 1993; Mears, Jr. 1993). 

This last pulse is roughly contemporaneous with a period 

of volcanism in the Basin and Range province and in 

northwestern Wyoming. Wyoming was elevated to 

almost its present elevation during the mid-Miocene. 

Recent erosion caused by the Belle Fourche River and its 

tributaries has exposed the current topographic 

expression of the tower. The alluvium, glacial materials, 

and other surficial deposits of Quaternary age fill major 

drainages in the area and continue to be deposited in a 

continental environment.
24 NPS Geologic Resources Division 

Figure 11. Generalized geologic time scale; adapted from the U.S. Geological Survey and International Commission on Stratigraphy. Red 

lines indicate major unconformities between eras. Included are major events in life history and tectonic events occurring on the North 

American continent. Absolute ages shown are in millions of years (Ma). Events specific to Devils Tower National Monument are discussed in 

the text. 
 DETO Geologic Resource Evaluation Report 25 

Figure 12. Location of the current Black Hills Uplift with regards to Precambrian terranes, northern Great Plains region. Modified from 

Lisenbee and DeWitt (1993). 
26 NPS Geologic Resources Division 

Figure 13. Plate tectonic schematic illustrating some of the Precambrian tectonic activity in the Black Hills region. In this drawing, the 

subducting lithosphere would represent the Trans-Hudson Province being subducted beneath the Wyoming Archean Province. The Black 

Hills and Devils Tower National Monument region would be located in the area of the Back-arc basin between 1,710 and 1,880 Ma. A similar 

tectonic setting exists today off the coast of China and Japan in the western Pacific Ocean. Graphic by Trista Thornberry-Ehrlich. 
 DETO Geologic Resource Evaluation Report 27 

Figure 14. Paleogeographic map of the Late Cambrian, about 500 Ma. The Transcontinental Arch is the narrow landmass that transects 

South Dakota, northwestern Nebraska, and Colorado. Relatively shallow water and nearshore environments occupy the region of the Black 

Hills while a deeper water basin (darker shade of blue) is forming in the area of the Williston Basin (WB). Modified from Dr. Ron Blakey, 

Northern Arizona University, http://jan.ucc.nau.edu/~rcb7/namC500.jpg (access February 27, 2006). 
28 NPS Geologic Resources Division 

Figure 15. Paleogeographic map of North America during the Early Mississippian Period, about 345 Ma. Note that much of the conterminous 

United States is covered with a shallow sea, including the area of the Black Hills, and the Transcontinental Arch has been breached. The 

Williston Basin (WB) continues to be a physiographic feature at this time. Modified from Dr. Ron Blakey, Northern Arizona University, 

http://jan.ucc.nau. edu/~rcb7/namM345.jpg (access February 27, 2006). 
 DETO Geologic Resource Evaluation Report 29 

Figure 16. Paleogeographic map of North America during the Early Triassic Period, about 245 Ma, during deposition of the upper Spearfish 

Formation. The landmasses had come together at this time to form the supercontinent, Pangaea. Inland and near the Equator, eastern 

Wyoming’s climate was hot and arid. The eventual Black Hills (BH) region was surrounded by lowlands containing redbeds and sabkha-like 

environments. Remnants of the Ancestral Rocky Mountains can still be seen in Colorado. Modified from Dr. Ron Blakey, Northern Arizona 

University, http://jan.ucc.nau.edu/~rcb7/namTr245.jpg (access February 27, 2006). 
30 NPS Geologic Resources Division 

Figure 17. Paleogeographic map of North America during the Jurassic Period, about 170 Ma. The Western Interior of North America has been 

inundated by shallow marine environments. BH: eventual Black Hills region. Modified from Dr. Ron Blakey, Northern Arizona University, 

http://jan.ucc.nau.edu/~rcb7/namJ170.jpg (access February 27, 2006). 
 DETO Geologic Resource Evaluation Report 31 

Figure 18. Western Interior Seaway during the Cretaceous, about 85 million years ago. Relatively shallow water covered the Devils Tower 

National Monument region at this time. BH: eventual Black Hills area. Modified from Dr. Ron Blakey, Northern Arizona University, 

http://jan.ucc.nau.edu/~rcb7/namK85.jpg (access February 27, 2006). 
32 NPS Geologic Resources Division 

Figure 19. Paleogeography of the Black Hills region near the end of the Laramide Orogeny approximately 40 Ma. The Black Hills uplift is the 

easternmost expression of the Laramide Orogeny. PRB: Powder River Basin, which formed west of the Black Hills. WB: Williston Basin. 

Both basins are prolific hydrocarbon-producing basins. Modified from Dr. Ron Blakey, Northern Arizona University, 

http://jan.ucc.nau.edu/~rcb7/namPe40.jpg (access February 14, 2008). 
 DETO Geologic Resource Evaluation Report 33 

Glossary 

This glossary contains brief definitions of technical geologic terms used in this report. Not all 

geologic terms used are referenced. For more detailed definitions or to find terms not listed 

here please visit http://wrgis.wr.usgs.gov/docs/parks/misc/glossarya.html. 

active tectonic margin. A continental margin at which 

there is significant seismicity and deformation caused 

by tectonic plate convergence. 

alloclastic breccia. A breccia that is formed by disruption 

of nonvolcanic rocks by volcanic processes beneath 

Earth’s surface; a type of volcanic breccia. 

alluvial fan. A fan-shaped deposit of sediment that 

accumulates where a high gradient stream flows out of 

a mountain front into an area of lesser gradient such as 

a valley. 

alluvium. Stream-deposited sediment that is generally 

rounded, sorted, and stratified. 

aquifer. Rock or sediment that are sufficiently porous, 

permeable, and saturated to be useful as a source of 

water. 

axis (fold). A straight line approximation that when 

moved parallel to itself generates the shape of a fold. 

basement. The undifferentiated rocks, commonly 

igneous and metamorphic, that underlie the rocks of 

interest. 

basin (structural). A doubly-plunging syncline in which 

rocks dip inward from all sides (also see dome). 

basin (sedimentary). Any depression, from continental 

to local scales, into which sediments are deposited. 

beach. A gently sloping shoreline covered with sediment, 

often formed by action of waves and tides. 

bed. The smallest sedimentary strata unit, commonly 

ranging in thickness from one centimeter to a meter or 

two and distinguishable from beds above. 

bedding. Depositional layering or stratification of 

sediments. 

block (fault). A crustal unit bounded by faults, either 

completely or in part. 

breccia. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented angular 

clasts. 

calcareous. A rock or sediment containing calcium 

carbonate. 

carbonaceous. A rock or sediment with considerable 

carbon, esp. organics, hydrocarbons, or coal. 

clastic. Rock or sediment made of fragments or preexisting rocks. 

clay. Clay minerals or sedimentary fragments the size of 

clay minerals (<2 cm). 

cone-in-cone. A sedimentary structure that resembles a 

set of concentric cones fitting one into another in 

inverted positions (base upward, apex downward). 

conglomerate. A coarse-grained sedimentary rock with 

clasts larger than 2 mm in a fine-grained matrix. 

craton. The relatively old and geologically stable interior 

of a continent. 

cross-stratification. Arrangement of strata inclined at an 

angle to the main, relatively horizontal layers of 

sedimentary rock. 

crust. The outermost compositional shell of Earth, 10-40 

km (6-25 mi) thick, consisting predominantly of 

relatively low-density silicate minerals. 

crystalline. Describes the structure of a regular, orderly, 

repeating geometric arrangement of atoms 

debris flow. A rapid and often sudden flow or slide of 

rock and soil material involving a wide range of types 

and sizes. 

deformation. A general term for the process of faulting, 

folding, shearing, extension, or compression of rocks 

as a result of various Earth forces. 

delta. A sediment wedge deposited at a stream’s mouth 

where it flows into a lake or sea. 

dike. A tabular igneous intrusion that cuts across or is at 

an angle to the orientation of adjacent rocks. 

dip. The angle between a structural surface and a 

horizontal reference plane measured normal to their 

line of intersection. 

dome. A doubly plunging anticline that dips radially in all 

directions. 

eolian. Formed, eroded, or deposited by or related to the 

action of the wind. 

eustatic. Relates to simultaneous worldwide rise or fall 

of sea level in Earth’s oceans. 

evaporite. Chemically precipitated mineral(s) formed by 

the evaporation of solute-rich water under restricted 

conditions. 

extrusive. Of or pertaining to the eruption of igneous 

material onto the surface of Earth. 

fault. A subplanar break in rock along which relative 

movement occurs between the two sides. 

feldspar. A group of framework silicates, containing 

aluminum and calcium, sodium, or potassium; 

feldspars are the most abundant minerals in Earth’s 

crust. 

fissle. A property of splitting easily along closely spaced 

parallel planes. 

foreland (tectonic). The exterior area of an orogenic belt 

where deformation occurs without significant 

metamorphism. Generally the foreland is closer to the 

continental interior than other portions of the 

orogenic belt. 

foreland basin. A linear sedimentary basin in a foreland 

These basin subside in response to flexural loading of 

the lithosphere by thrust sheets. 

formation. Fundamental rock-stratigraphic unit that is 

mappable and lithologically distinct from adjoining 

strata and has definable upper and lower contacts. 

fracture. Irregular breakage of a mineral; also any break 

in a rock (e.g., crack, joint, fault) 

igneous. Refers to a rock or mineral that originated from 

molten material; one of the three main classes or rocks: 

igneous, metamorphic, and sedimentary. 
34 NPS Geologic Resources Division 

intrusion. A body of igneous rock that invades older 

rock. The invading rock may be a plastic solid or 

magma that pushes its way into the older rock. 

joint. A semi-planar break in rock without relative 

movement of rocks on either side of the fracture 

surface. 

karst topography. Topography characterized by 

abundant sinkholes and caverns formed by the 

dissolution of calcareous rocks. 

laccolith. A tack head- to arcuate-shaped pluton that 

domed or up-arched the overlying country rocks and 

whose basal contact is parallel to the orientation of 

adjacent strata. 

landslide. Any process or landform resulting from rapid 

mass movement under relatively dry conditions. 

lava. Magma that has been extruded out onto Earth’s 

surface, both molten and solidified. 

lopolith. A large, typically layered igneous intrusion 

whose floor is concave and whose roof may be 

concave or flat. 

lithosphere. The relatively rigid outmost shell of Earth’s 

structure, 50 to 100 km (31 to 62 mi) thick, that 

encompasses the crust and uppermost mantle. 

mafic. A rock, magma, or mineral rich in magnesium and 

iron. 

magma. Molten rock generated within Earth that is the 

parent of igneous rocks. 

mantle. The zone of Earth’s interior between crust and 

core. 

matrix. The fine-grained interstitial material between 

coarse grains in porphyritic igneous rocks and poorly 

sorted clastic sediments or rocks. 

member. A lithostratigraphic unit with definable contacts 

that subdivides a formation. 

metamorphic. Pertaining to the process of 

metamorphism or to its results. 

metamorphism. Literally, “change in form”. 

Metamorphism occurs in rocks with mineral 

alteration, genesis, and/or recrystallization from 

increased heat and pressure. 

monocline. A one-limbed flexure in strata, which are 

usually flat-lying except in the flexure itself. 

neck (volcanic). An eroded, semi-vertical, pipe-like 

discordant pluton that represents the vent of a 

volcano. 

normal fault. A dip-slip fault in which the hanging wall 

moves down relative to the footwall. 

orogeny. A mountain-building event, particularly a wellrecognized event in the geological past (e.g. the 

Laramide Orogeny). 

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface. 

paleogeography. The study, description, and 

reconstruction of the physical geography from past 

geologic periods. 

Pangaea. A theoretical, single supercontinent that 

existed during the Permian and Triassic Periods (also 

see Laurasia and Gondwana). 

passive tectonic margin. A continental boundary formed 

by rifting (pulling apart) and continental rupture and 

without plate-boundary tectonism. 

pebble. Generally, small, rounded, rock particles from 4 

to 64 mm in diameter. 

phenocrysts. A coarse crystal in a porphyritic igneous 

rock. 

phonolite. A group of fine-grained extrusive rocks 

primarily composed of feldspar minerals. 

pluton. A body of intrusive igneous rock crystallized at 

some depth in Earth. 

porphyry. An igneous rock with abundant coarse crystals 

in a fine-grained groundmass. 

pyroxene. A group of dark rock-forming silicate 

minerals. 

red beds. Sedimentary strata composed largely of 

sandstone, siltstone, and shale that are predominantly 

red due to the presence of ferric oxide (hematite) 

coating individual grains. 

regression. A long-term seaward retreat of the shoreline 

or relative fall of sea level. 

reverse fault. A contractional, high angle (>45°), dip-slip 

fault in which the hanging wall moves up relative to the 

footwall (also see thrust fault). 

ripple marks. The undulating, subparallel, usually smallscale, ridge pattern formed on sediment by the flow of 

wind or water. 

sabkha. A coastal environment in an arid climate where 

evaporation rates are high. 

sandstone. Clastic sedimentary rock of predominantly 

sand-sized grains. 

scarp. A steep cliff or topographic step resulting from 

vertical displacement on a fault or by mass movement. 

sediment. An eroded and deposited, unconsolidated 

accumulation of lithic and mineral fragments. 

sedimentary rock. A consolidated and lithified rock 

consisting of detrital and/or chemical sediment(s). 

shale. A clastic sedimentary rock made of clay-sized 

particles that exhibit parallel splitting properties. 

sill. A tabular, igneous intrusion that parallels the 

orientation of adjacent strata. 

silt. Clastic sedimentary material intermediate in size 

between fine-grained sand and coarse clay (1/256-1/16 

mm). 

siltstone. A variable-lithified sedimentary rock with siltsized grains. 

stock. An igneous intrusion exposed less than 104 sq km 

(40 sq mi) at the surface. 

strata. Tabular or sheetlike masses or distinct layers (e.g., 

of rock). 

stratigraphy. The geologic study of the origin, 

occurrence, distribution, classification, correlation, 

age, etc. of rock layers, especially sedimentary rocks. 

stream. Any body of water moving under gravity flow 

and confined within a channel. 

subduction zone. A convergent plate boundary where 

oceanic lithosphere descends beneath a continental or 

oceanic plate and is carried down into the mantle. 

subsidence. The gradual sinking or depression of part of 

Earth’s surface. 

talus. Rock fragments of any size or shape derived from 

and lying at the base of a cliff or very steep, rocky 

slope. 

tectonic. Relating to large-scale movement and 

deformation of Earth’s crust. 

terrane. A region or group of rocks with similar geology, 

age, or structural style. 

terrestrial. Relating to Earth or Earth’s dry land. 
 DETO Geologic Resource Evaluation Report 35 

thrust fault. A contractional, dip-slip fault with a 

shallowly dipping fault surface (<45°) where the 

hanging wall moves up and over relative to the 

footwall. 

thrust sheet. The body of rock above a large-scale thrust 

fault whose surface is horizontal or very gently 

dipping. 

topography. The general morphology of Earth’s surface 

including relief and location of natural and 

anthropogenic features. 

transgression. Landward migration of the sea due to a 

relative rise in sea level. 

trend. The direction or azimuth of elongation or a linear 

geological feature. 

turbidite. A sediment or rock deposited from, or inferred 

to have been deposited from, a turbidity (density) 

current. 

unconformity. A surface within sedimentary strata that 

marks a prolonged period of nondeposition or 

erosion. 

uplift. A structurally high area in the crust, produced by 

movement that raises the rocks. 

vent. An opening at the surface of Earth where volcanic 

materials emerge. 

volcanic. Related to volcanoes; describes igneous rock 

crystallized at or near Earth’s surface (e.g., lava). 

weathering. The set of physical, chemical, and biological 

processes by which rock is broken down in place. 
36 NPS Geologic Resources Division 

References 

This section lists references cited in this report. A more complete geologic bibliography is 

available from the National Park Service Geologic Resources Division. 

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and S. M. Roberts, 164-187. Geological Survey of 

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Brenner, R. L. 1983. Late Jurassic tectonic setting and 

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In Mesozoic paleogeography of the west-central United 

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Society of Economic Paleontologists and 

Mineralogists, Rocky Mountain Section, Rocky 

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Brenner, R. L., and J. A. Peterson. 1994. Jurassic 

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the Rocky Mountain region, USA, ed. M. V. Caputo, J. A. 

Peterson, and K. J. Franczyk, 217-232. Society for 

Sedimentary Geology, Rocky Mountain Section. 

Carpenter, F.R. 1888. Notes on the ecology of the Black 

Hills. Rapid City: Preliminary report of the South 

Dakota School of Mines. 

Darton, N.H. 1909. Geology and water resources of the 

northern portion of the Black Hills and adjoining 

regions in South Dakota and Wyoming. Professional 

Paper 65. Denver, CO: U.S. Geological Survey. 

Davis, A. D., and F. Beaver. 2002. Engineering problems 

of gypsum karst along the Interstate 90 development 

corridor in the Black Hills, South Dakota. Geological 

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Dickinson, W. R. 1974. Plate tectonics and 

sedimentation. In Tectonics and sedimentation, ed. W. 

R. Dickinson, 1-27. Society of Economic 

Paleontologists and Mineralogists, Special Publication 

22. 

Dickinson, W. R., and W.S. Snyder. 1978. Plate tectonics 

of the Laramide Orogeny. In Laramide folding 

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Society of America, Memoir 151. 

Driscoll, D. G., J. M. Carter, J. E. Williamson, and L. D. 

Putman. 2002. Hydrology of the Black Hills area, South 

Dakota. U.S. Geological Survey, Water-Resources 

Investigations Report 02-4094. 

http://www.pubs.usgs.gov /wri/wri024094/pdf 

(accessed February 9, 2006). 

Dubiel, R. F. 1994. Triassic deposystems, 

paleogeography, and paleoclimate of the Western 

Interior. In Mesozoic Systems of the Rocky Mountain 

Region, USA, ed. M. V. Caputo, J. A. Peterson, and K. J. 

Franczyk, 133-168. Society for Sedimentary Geology, 

Rocky Mountain Section. 

Dutton, C.E., and G.M. Schwartz. 1936. Notes on the 

jointing of the Devil’s Tower, Wyoming. Journal of 

Geology 44 (6): 717-728. 

Effinger, W. L. 1934. A report on the geology of Devils 

Tower National Monument. National Park Service. 

http://www.cr.nps.gov/history/online_books/berkeley

/effinger1/index.htm (accessed March 1, 2006). 

Epstein, J. B. 2002. Gypsum-anhydrite karst in the Black 

Hills, South Dakota-Wyoming. Geological Society of 

America Abstracts with Programs 34: 116. 

Epstein, J. B. 2003. Gypsum karst in the Black Hills, 

South Dakota-Wyoming: Geomorphic development, 

hazards, and hydrology. Circular. Norman: Oklahoma 

Geological Survey. 

Erslev, E. A. 1993. Thrusts, back-thrusts, and detachment 

of Rocky Mountain foreland arches. In Laramide 

basement deformation in the Rocky Mountain foreland 

of the western United States, ed. C. J. Schmidt, R. B. 

Chase, and E. A. Erslev, 339-358. Geological Society of 

America, Special Paper 280. 

Flanagan, K. M., and J. Montagne. 1993. Neogene 

stratigraphy and tectonics of Wyoming. In Geology of 

Wyoming, ed. A. W. Snoke, J. R. Steidtmann, and S. M. 

Roberts, 572-607. Geological Survey of Wyoming, 

Memoir 5. 

Gries, R. 1983. North-south compression of Rocky 

Mountain foreland structures. In Rocky Mountain 

foreland basins and uplifts, ed. J. D. Lowell and R. 

Gries, 9-32. Rocky Mountain Association of 

Geologists. 

Guyer, G. S. 2000. Paleoenvironments of the Jurassic 

Gypsum Spring Formation, Bighorn Basin, Wyoming. 

MS thesis, Iowa State University. 

Hallam, A. 1988. A reevaluation of Jurassic eustasy in 

light of new data and the revised Exxon curve. In SeaLevel changes – an integrated approach, ed. C. K. 

Wilgus, B. S. Hastings, H. Posamentier, V. Wagoner, C. 

A. Ross, and C. G. Kendall, 261-273. Society of 

Economic Paleontologists and Mineralogists, Special 

Publication 42. 
 DETO Geologic Resource Evaluation Report 37 

Halvorson, D. L. 1980. Geology and petrology of the 

Devils Tower, Missouri Buttes, and Barlow Canyon 

area, Crook County, Wyoming. PhD diss, University of 

North Dakota. 

Harp, Edwin L., and Charles R. Lindsay. 2005. Stability 

of Leaning Column at Devils Tower National 

Monument, Wyoming. Denver: U.S. Geological 

Survey, Central Geologic Hazards Team. Report 

conveyed to Superintendent Lisa Eckert, Devils Tower 

National Monument, October 6, 2005. 

Jaggar Jr., T. A. 1901. Laccoliths of the Black Hills. U.S. 

Geological Survey 21st Annual Report (3). 

Karner, F. R., and D. L. Halvorson. 1987. The Devils 

Tower, Bear Lodge Mountains, Cenozoic igneous 

complex, northeastern Wyoming. In Rocky Mountain 

Section of the Geological Society of America, ed. S. S. 

Beus, 161-164. Geological Society of America, 

Centennial Field Guide 2. 

Karner, F. R., and D. L. Halvorson. 1989. Devils Tower 

and the Missouri Buttes. In Devils Tower – Black Hills 

alkalic igneous rocks and general geology, ed. F. R. 

Karner, 67-69. Field Trip Guidebook T131. 

Washington, D.C.: American Geophysical Union. 

Kauffman, E. G. 1977. Geological and biological 

overview: Western Interior Cretaceous basin. 

Mountain Geologist (14): 75-99. 

Kiver, E. P., and D. V. Harris. 1999. Geology of U.S. 

parklands. 5th ed. New York: John Wiley & Sons, Inc. 

Kvale, E. P., G. D. Johnson, D. L. Mickelson, K. Keller, L. 

C. Furer, and A. W. Archer. 2001. Middle Jurassic 

(Bajocian and Bathonian) dinosaur megatracksites, 

Bighorn Basin, Wyoming, U.S.A. Palaios (16): 233-254. 

Lisenbee, A. L., and E. DeWitt. 1993. Laramide evolution 

of the Black Hills uplift. In Geology of Wyoming, ed. A. 

W. Snoke, J. R. Steidtmann, and S. M. Roberts, 374-

412. Geological Survey of Wyoming, Memoir 5. 

Mears, Jr., B. 1993. Geomorphic history of Wyoming and 

high-level erosion surfaces. In Geology of Wyoming, ed. 

A. W. Snoke, J. R. Steidtmann, and S. M. Roberts, 608-

626. Geological Survey of Wyoming, Memoir 5. 

Mickelson, D. L., E. P. Kvale, G. D. Johnson, M. R. King, 

K. A. Mickelson, and P. Getty. 2005. Subaqueous 

tetrapod swim tracks from the Middle Jurassic; Big 

Horn Basin, Wyoming, U.S.A. Geological Society of 

America Abstracts with Programs 37: 37. 

Miller, E. L., M. M. Miller, C. H. Stevens, J. E. Wright, 

and R. Madrid. 1992. Late Paleozoic paleogeographic 

and tectonic evolution of the western U.S. cordillera. 

In The Cordilleran Orogen: Conterminous U.S., ed. B. C. 

Burchfiel, P. W. Lipman, and M. L. Zoback, 57-106. 

Geological Society of America, The Geology of North 

America G-3. 

National Park Service. 2001. Final general management 

plan/ environmental impact statement, Devils Tower 

National Monument. National Park Service. 

http://www.nps.gov/deto/gmp_final/pdf/final_gmp.pd

f (accessed March 1, 2006). 

Parcell, W. C., and M. K. Williams. 2003. Thrombolite 

buildups in the Middle Jurassic Piper and Gypsum 

Spring Formations, Bighorn Basin, Wyoming. 

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Meeting Expanded Abstracts 12: 132. 

Peterson, F. 1994. Sand dunes, sabkhas, streams, and 

shallow seas: Jurassic paleogeography in the southern 

part of the Western Interior Basin. In Mesozoic Systems 

of the Rocky Mountain Region, USA, ed. M. V. Caputo, 

J. A. Peterson, and K. J. Franczyk, 233-272. Society for 

Sedimentary Geology, Rocky Mountain Section. 

Picard, M. D. 1993. The Early Mesozoic history of 

Wyoming. In Geology of Wyoming, ed. A. W. Snoke, J. 

R. Steidtmann, and S. M. Roberts, 210-248. Geological 

Survey of Wyoming, Memoir 5. 

Picard, M. D. 1997. Mesozoic history of Wyoming. In 

Proceedings of the 32nd annual forum on the geology of 

industrial minerals, ed. R. W. Jones and R. E. Harris, 

73-106. Geological Survey of Wyoming. 

Pipiringos, G. N., and R. B. O’Sullivan. 1978. Principal 

unconformities in Triassic and Jurassic rocks, Western 

Interior United States – a preliminary survey. 

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Ploynoi, M., and W. C. Parcell. 2005. Developing of 

Middle Jurassic microbial buildups in Bighorn Basin, 

Wyoming. Geological Society of America Abstracts with 

Programs 37: 17. 

Redden, J. A., Z. E. Peterman, R. E. Zartman, and E. 

DeWitt. 1990. U-Th-Pb geochronology and 

preliminary interpretation of Precambrian tectonic 

events in the Black Hills, South Dakota. In The Early 

Proterozoic Trans-Hudson Orogen of North America, 

ed. J. F. Lewry and M. R. Stauffer, 229-251. Geological 

Association of Canada, Special Paper 37. 

Robinson, C. S. 1956. Geology of the Devils Tower 

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Robinson, C. S. 1998. Geology of Devils Tower National 

Monument, Wyoming. Devils Tower Natural History 

Association. 

Sabel, J. M. 1981. The sedimentology of the Spearfish 

Formation. MS thesis, South Dakota Schools of Mines 

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Sabel, J.M. 1984. Sedimentology and depositional history 

of the Permo-Triassic Spearfish Formation, 

southwestern Black Hills, South Dakota. In The 

Permian and Pennsylvanian Geology of Wyoming, ed. J. 

Goolsby , and D. Morton, 295-309, 35th Annual Field 

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tectonic evolution of the western U.S. cordillera. In 

The Cordilleran Orogen: Conterminous U.S., ed. B. C. 

Burchfiel, P. W. Lipman, and M. L. Zoback, 107-168. 

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America G3. 

Schmude, D. 1999. Interplay of uplift, erosion, 

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Steidtmann, J. R. 1993. The Cretaceous foreland basin 

and its sedimentary record. In Geology of Wyoming, ed. 

A. W. Snoke, J. R. Steidtmann, and S. M. Roberts, 250-

271. Geological Survey of Wyoming, Memoir 5. 

Steidtmann, J. R., L. T. Middleton, and M. W. Shuster. 

1989. Post-Laramide (Oligocene) uplift in the Wind 

River Range, Wyoming. Geology 17: 38-41. 

Strahler, A. N. 1960. Physical Geography. 2nd ed. New 

York: John Wiley & Sons. 

Williams, M. K., and W. C. Parcell. 2003. Stratigraphic 

relationships within the Middle Jurassic Gypsum 

Spring Formation (Bajocian and Bathonian), Bighorn 

Basin, Wyoming and Montana. American Association of 

Petroleum Geologists Annual Meeting Expanded 

Abstracts 12: 181-182. 

 
 DETO Geologic Resource Evaluation Report 39 

Appendix A: Geologic Map Graphic 

The following page is a snapshot of the geologic map for Devils Tower National Monument. 

For a poster-size PDF of this map or for digital geologic map data, please see the included 

CD or visit the Geologic Resource Evaluation publications Web page 

(http://www.nature.nps.gov/geology/inventory/gre_publications.cfm). 

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. 

Devils Tower National Monument 

Geologic Resource Evaluation Report 

Natural Resource Report NPS/NRPC/GRD/NRR—2008/046 

NPS D-86, September 2008 

National Park Service 

Director • Mary A. Bomar 

Natural Resource Stewardship and Science 

Associate Director • Bert Frost 

Natural Resource Program Center 

The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and 

Science Directorate. The Center Director is located in Fort Collins, with staff located principally in 

Lakewood and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air 

Resources Division, Biological Resource Management Division, Environmental Quality Division, Geologic 

Resources Division, and Water Resources Division. NRPC also includes three offices: The Office of 

Education and Outreach, the Office of Inventory, Monitoring and Evaluation, and the Office of Natural 

Resource Information Systems. In addition, Natural Resource Web Management and Partnership 

Coordination are cross-cutting disciplines under the Center Director. The multidisciplinary staff of NRPC 

is dedicated to resolving park resource management challenges originating in and outside units of the 

national park system. 

Geologic Resources Division 

Chief • Dave Steensen 

Planning Evaluation and Permits Branch Chief • Carol McCoy 

Credits 

Author • John Graham

Review • Rachel Benton and Carol McCoy 

Editing • Thomas W. Judkins, Sid Covington, and Melanie Ransmeier 

Digital Map Production • Stephanie O'Meara and Trista Thornberry-Ehrlich 

Map Layout Design • Melanie Ransmeier
Geologic Resources Division 

Natural Resource Program Center 

P.O. Box 25287 

Denver, CO 80225 

http://www.nature.nps.gov/geology/inventory/ 

(303) 969-2090 

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U.S. Department of the Interior