Geology of Badlands National Park: A Preliminary Report 

By Philip W. Stoffer1 

Open-File Report 03-35 

2003

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey 

editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or 

firm names if for descriptive purposes only and does not imply endorsement by the U.S. 

Government.

U.S. Department of the Interior 

U.S. Geological Survey 

1

U.S. Geological Survey, Menlo Park, California 
Table of Contents 

Introduction...................................................................................................... 1 

How the Badlands became a national park................................................... 1 

Maps of Badlands National Park................................................................ 2 

Physiographic setting.............................................................................. 3 

Regional geology, structure, and landscape............................................... 3 

Geologic time scale.................................................................. 3

Ancient rocks and structures........................................................... 4 

The Western Interior Seaway......................................................... 6 

The Tertiary “White River” world...................................................... 6 

The Quaternary landscape............................................................. 7 

Stratigraphy and Geologic Structures in the North Unit.............................................. 8 

Geologic Structures................................................................................. 8 

Composite Stratigraphic Section................................................................ 9 

Cretaceous Geology of Badlands National Park........................................................12 

Resolving Cretaceous geology through paleontology...................................... 12 

Cretaceous stratigraphy of Badlands National Park........................................ 14 

 Pierre Shale........................................................................... 14 

History of Pierre Shale Nomenclature..................................... 14 

 DeGrey facies................................................................... 15 

 Verendrye facies................................................................ 17 

 The Campanian-Maestrichtian boundary unconformity.............. 21 

 Virgin Creek facies............................................................ 22 

 Mobridge facies................................................................ 25 

 Elk Butte facies ................................................................ 27 

 Fox Hills Formation...................................................................... 30 

The Cretaceous-Tertiary boundary in Badlands National Park..................................... 35 

A historical perspective on the Interior Zone ......................................... 36 

The Disturbed Zone.................................................................................37 

 Conata Creek locality................................................................... 39 

Grassy Tables Overlook locality.......................................................40

Wilderness Access Trailhead locality.............................................. 42 

Buffalo Gap National Grasslands locality.......................................... 43 

Dry Creek locality......................................................................... 44 

Unnamed marine facies (upper Fox Hills Formation)..................................... 44 

Tertiary Geology of Badlands National Park............................................................ 46 

Historical overview of the White River Group................................................ 47 

The Yellow Mounds and Interior paleosols.................................................... 47 

Chamberlain Pass Formation.....................................................................49 

Chadron Formation.................................................................................. 49 

Brule Formation.......................................................................................51 

 The Pig Dig site........................................................................... 52 

 Sharps Formation.................................................................................... 53 

The Quaternary Landscape..................................................................................53 

Three rivers over time...............................................................................54 

Stream terraces: can they tell us about past climatic conditions?....................... 55 

Quaternary and late Tertiary time scale (stages and stades).............................55 

Weathering, mass wasting, and erosion....................................................... 57 

Castles, monuments, sod tables, and hoodoos.............................................. 59 

Acknowledgments.............................................................................................. 60 

Selected Internet links......................................................................................... 60 

Selected references............................................................................................ 60 

ii 

 
Introduction 

Badlands National Park is host to perhaps the most scenic 

geology and landscape features in the Western Interior

region of the United States. Ongoing erosion that forms the 

“badlands” exposes ancient sedimentary strata (fig. 1). This 

report provides a basic overview of the geology of the park. 

The discussions presented within include both wellestablished concepts and theories and new, preliminary data 

and interpretations. Much emphasis is placed on presenting 

information about the oldest and least studied rocks in the

park (those that underlie the White River beds throughout

the park region). A reference list provided includes many

important published sources used in the preparation of this 

report. However, the volume of literature about the geology 

and paleontology of the Badlands region is immense, 

probably in range of thousands of publications. 

How the Badlands Became a National Park 

Although travelers and homesteaders called them

“badlands” because of their rugged, desolate appearance a

their lack of value for farming, the scenic descriptions these

people returned east with added to the romantic call of the 

West. The value of the Badlands’ paleontological reso

was recognized in the early stages of exploration of the 

Nebraska Territory. Numerous fossil-collecting expedit

early in last century resulted in compilation of research and

display collections in eastern American field museums. A 

perusal of the geologic literature of the Badlands regi

through time tells a story of changing thoughts and attitudes towards the land and its resources. 

Historically, research in the Badlands has focused on the fossil-rich terrestrial deposits (bone beds) of the 

Tertiary White River Group. Unfortunately, enthusiasm by amateur, private, and commercial collectors 

lead to the perceived over-exploitation of these resources, especially after a rail line linked the South

Dakota towns of Interior and Scenic to the main rail lines in Rapid City. Efforts to preserve the uniquel

scenic geologic setting led to the establishment of Badlands National Monument in 1929. Badlands 

a national park by an Act of Congress in 1978 (see location maps, figs. 2 and 3). Today, all fossil, rock, 

plant, and animal resources are protected in the park and must remain where you find them. 

nd 

urces

ions

on

y

became

1 

 
Maps of Badlands National Park 

2 

 
Physiographic Setting 

Badlands National Park is located on the high Great Plains of southwestern South Dakota east of the Black 

Hills. The highest elevation in the park is 3282 ft (1000m) on Sheep Mountain; the lowest elevation is 2460

ft (750 M) along Sage Creek along the northern park boundary. The park receives an average of between 15

and 16 inches of rain per year, mostly in the form of thunderstorm activity that peaks in late June. By 

comparison, only a trace of precipitation occurs during the fall and winter months. The average high 

temperature for the month of July is around 91 degrees F (with some days rising into the 100s); January 

averages a low of 32 degrees F (with some lows in the sub zero range). These climatic conditions are the 

essential ingredients of the American short grass prairies (or steppes) of the high plains. These climatic 

conditions unite with the local geologic setting to form the essential ingredients for the formation of 

“badlands” topography. The cold, dry winters and the hot summers limit the vegetation to short grasses and

sedges on sunny exposures, to juniper and shrub oak communities in the cooler, shady, and wetter areas 

along ravines. 

By comparison, the terrestrial strata of the White River Group lacks the essential nutrients for plants, 

whereas the underlying Cretaceous marine shale beds are rich in phosphorus, potassium, and iron. As a 

consequence, the Cretaceous strata are generally very poorly exposed beneath thick ground cover except

along stream cut banks. In contrast, the White River beds form the steep upper hillsides of mostly barren 

white, red, and gray strata. Infrequent summer thunderstorms loosen and quickly erode the poorly 

consolidated sediments resulting in the development of badlands-style topography along escarpments. In

the badlands region, escarpments have developed along the valleys of the White and Cheyenne River 

valleys and their tributaries. These escarpments formed in association with Quaternary erosion cycles - the 

episodic rapid down cutting by streams during wet periods followed by the gradual expansion of flood 

plains during dry periods. The Badlands Escarpment in the North Unit is also controlled in part by gradual

on-going uplift along faults. 

Regional Geology, Structure, and Landscape 

The spectacular landscape in Badlands National Park is a reflection of ongoing erosional forces carving 

bedrock consisting of sedimentary rock formations. The exposed sedimentary strata preserve a record of

more ancient geologic events and processes including changing depositional environments and the tectonic

uplift and folding of rock layers in the Earth’s crust. These strata and the fossils they preserve reveal 

evidence for gradual changes in the regional and global Earth system (such as uplift of the Rocky

Mountains or changes in sea level and climate over time) or distant catastrophic events (such as the effects 

massive volcanic eruptions or asteroid impacts). A significant physiographic factor influencing the 

landscape of Badlands National Park is its proximity to rivers draining the high plains east of the Black 

Hills. The core of the “badlands” (meaning the “badlands” associated with Badlands National Park) is part 

of a dissected plateau region bounded by the Cheyenne River (to the north and west), the Bad River (to the 

east), and the White River (to the south). The word, badlands, applies to any region where erosion in poorly

consolidated sediments creates a rugged and barren landscape. 

Geologic Time Scale 

Fig. 4 is a general geologic time scale that shows named divisions of time used in North America. This

table only provides detail for geologic names used in this report. Geologic time is subdivided into unit rank

from largest to smallest time intervals: era, period, epoch. Epochs are also subdivided into stages (some of 

these smaller subdivisions are mentioned later in the text); epochs are only shown for the Cretaceous and 

younger periods on Fig 4. Subdivisions of Precambrian time are not shown.

3 

 
Ancient Rocks and Structures 

The sedimentary layers exposed at the surface in the area are only a fraction of a thick blanket of 

sedimentary rock formations that blanket the high Great Plains region (fig. 5). Sedimentary rocks overlie a 

“basement” of even more ancient crust consisting of igneous and metamorphic rocks, similar to those 

exposed throughout the core of the Black Hills, or in smaller exposures east of the Missouri River or in the 

Canadian Shield region far to the northeast. The age of these basement rocks is measured in billions of

years. Wells drilled in search of water and petroleum reveal that the blanket of sedimentary rock above the 

basement ranges varies in thickness across the region. Over time, in regions where the bedrock sank

sedimentary basins formed. Areas where the land rose or folded upward are called arches or uplifts. 

4 

 
This blanket of sedimentary material that overlies the ancient basement rocks began to accumulate nearly 

half a billion years ago as erosion allowed the advance of the Cambrian sea across the region. Over the next

half billion years, shallow seas advanced and retreated across the region many times as the land gradually 

rose or sank. The sedimentary blanket is thickest in regions where the land subsided relative to surrounding

regions. Deep sedimentary basins in the region include the Williston Basin (in North Dakota and Montana) 

and the Powder River Basin (in eastern Wyoming). In portions of these basins, the sedimentary sequence is

over 4,000 meters thick. However, in the Badlands National park area this sedimentary blanket is only

about 1,000 meters thick. Records from oil drilling on anticlines such as the Cedar Creek Arch (in

northwestern South Dakota) reveal that some basins and intervening uplifts formed gradually over time, 

whereas others grew in relatively short “pulses” such as occurred with the initial uplift of the modern

Rocky Mountains (including the Black Hills) that began rising about 70 million years ago. As the Black 

Hills rose, erosion gradually stripped away materials. Today we can see a profile of this great sedimentary 

blanket in an outcrop belt of hogbacks along the flanks of the Black Hills. Water well drilling in the park 

area reveals that many of the same rock units exposed along the eastern flank of the Black Hills also occur 

beneath the park. 

The geologic setting of the park’s North Unit is controlled in part by the Sage Creek Arch, a long

southeast-to-northwest-trending system of folds and faults that roughly parallels the park’s northern

boundary. Many other structural features are known throughout the region. As these uplifts developed, they

5 

 
influenced the pattern of sediment deposition across the region through time. The rock record for the 

Paleozoic Era (between 570 and 230 million years ago) is dominated by limestone formations formed from

calcareous sediments deposited in shallow seas. Starting in the late Paleozoic, uplift in the region began to

generate large quantities of clastic sediments (mostly sand and clay) that filled in basins across the region. 

Through the Triassic and Jurassic Periods of the Mesozoic Era additional sediments were episodically 

deposited across the Badlands region. Rivers draining westward for the Appalachian region drained into a 

low, subdued landscape. Sedimentary rocks of the Triassic and Early Jurassic are “red beds” - typically 

consisting of layers of mudrock, sandstone, and gypsum deposited in a hot, arid, subtropical climate. By

Jurassic time, the Cordilleran Mountain belt was actively developing. The development of the volcanic 

chains, such as those that formed the ancestral core or the Sierra Nevada, eventually blocked westward

draining river systems. Ongoing volcanism and mountain building along the West Coast began the events

that lead to the formation of the Western Interior Seaway in the Cretaceous Period. 

The Western Interior Seaway

The oldest rocks exposed in the park formed from sediments 

deposited nearly 75 million years ago in the Western Interior

Seaway, a broad, shallow inland sea that once extended from the 

Gulf of Mexico to the Arctic Ocean. At its maximum extent roughly 

80 million years ago, this shallow inland sea extended from the 

Arctic Ocean to the Gulf of Mexico, and from the Wyoming/Idaho 

border region to perhaps the Mississippi Valley region (fig. 6). This

seaway gradually vanished as the rising Rocky Mountains 

progressively flooded the region with sediments and the land rose

above sea level. These strata consist of dark shale beds that contain 

remains of extinct species of marine organisms. These sediments, 

and other similar exposures across the region demonstrate that a 

great shallow seaway persisted across central North America. 

Marine waters began flooding the mid-continent region nearly 115 

million years ago (during the Early Cretaceous) as the Cordilleran 

mountain chain developed along the western margin of North 

America. This great seaway persisted for an additional 50 million years. In its final stages, sediment

pouring into the seaway basin from the developing western mountain ranges caused the final eastward

migration of the western shoreline. About this time, the last great dinosaurs of the Late Cretaceous (i.e., 

Tyrannosaurus and Triceratops) lived on a floodplain as the shoreline migrated into northwestern South

Dakota, but marine conditions persisted in the Badlands region. These floodplain deposits are preserved as 

the Hell Creek Formation in northwestern South Dakota, Montana, and North Dakota, whereas the

equivalent marine rocks make up the Fox Hills Formation and Pierre Shale in central South Dakota. 

Then a great catastrophe occurred. At least one great asteroid collided with Earth around 65 million years 

ago, causing a great mass extinction. On land, all dinosaurs and flying reptiles vanished, and in the sea, the 

ammonites, mosasaurs (large swimming reptiles), and other groups disappeared. The seaway eventually

completely disappeared from the region, and a whole new terrestrial ecosystem took its place. 

The Tertiary “White River” World 

During the early Tertiary, the landscape was dominated by broad, forested floodplains of ancient river 

systems draining from the west. Through the middle to late Tertiary, the landscape grew progressively 

higher and drier, yet still received sediments from the west, including ash falls from volcanic eruptions in

the Western Cordilleran region (now the Nevada region). Terrestrial sedimentation during the early to mid

Tertiary is responsible for the formation of the White River Group, the group of rock formation exposed in 

the “badlands” throughout the park region. The oldest sedimentary deposits of the White River Group

6 

 
formed in the Eocene Epoch, but the majority of the rock units formed during the following Oligocene 

Epoch. The youngest White River beds preserved in the park were deposited around 23 million years ago.

By about 50 million years ago, smaller brackish-water remnants of the Western Interior Seaway had 

completely vanished from the region, and a broad, low plain replaced it. Unlike today, the climate was 

warm and humid with abundant rainfall, producing a forested subtropical environment. Starting around 40

million years ago, sediments derived from the ancient core of the Black Hills and other areas began to fill 

in the broad low valleys that had developed across the landscape. River channel deposits and floodplain

sediments accumulated, and the soils formed from them. With dinosaurs out of the way, mammalian 

species began to spread and diversify. During the Oligocene Epoch (35-23 million years ago) many large

mammals adapted to the Badlands region. Many had appearances similar to modern species: Some

resembled deer-like creatures (Leptomeryx), a giant pig (Archaeotherium), small horses (Mesohippus), a 

saber-tooth cat (Hoplophoneus), rhinoceros/hippopotamus-like creatures (Subhyracodon and 

Metamynodon), squirrel-like (Ischromys), burrowing sheep-like animals (Oreodon), and a rabbit-like rodent

(Paleolagus). In addition, fish, turtles and other reptiles and birds flourished. 

Although volcanoes in the western states had dumped ash across the region many times throughout time, in

the late Oligocene several massive volcanic eruptions in the Nevada region dumped thick blankets of ash in

the badlands region. Also in the late Oligocene the climate began to change, becoming drier as the land

steadily began to rise. The record of sedimentation ends in the region in early Miocene time (around 20

million years ago). 

The White River beds in Badlands National Park consist of a group of several rock formations, each with 

unique sedimentary rocks and fossil flora and fauna. Named rock subdivisions within the Tertiary White

River Group exposed in the park include from oldest to youngest: the Chamberlain Pass Formation

(Eocene), the Chadron Formation (Eocene), the Brule Formation (Oligocene), and the Sharps Formation 

(Oligocene). 

The Quaternary Landscape 

From the late Tertiary through today erosion has dominated the landscape while the entire region slowly 

continues to rise. Although continental glaciers of the Quaternary period did not reach the Badlands area,

their influence on the river systems indirectly influenced the pattern of river drainages in the region. 

Climatic conditions in combination with bedrock characteristics are responsible for the formation of

unusual badlands topography throughout the park region. 

Although deposition of sediments probably continued in the park region after deposition of the Sharps

Formation (late Oligocene, about 23 million years ago), erosion has removed all evidence of younger 

Tertiary deposits (however, deposits of Miocene and younger age do occur in the region). Many of the 

landscape features we see today owe their origin to processes that have taken place over the last several

million years. On the highest hilltops in the park are coarse gravel deposits consisting of material derived

from stream deposits formed when the surface of the landscape was much higher than today. Erosion now 

dominates the landscape. In most areas, hundreds of meters of sediment have been stripped away by

erosion. The modern topographic distribution of the Badlands is a reflection the stream drainage patterns,

vegetation, and climatic conditions that have changed over time. 

The Quaternary Epoch began about 2 million years ago. In this time interval great continental glaciers 

developed in northern Canada and throughout the Rocky Mountain region. Several times continental

glaciers spread from Canada as far south as Nebraska and Kansas. Although these glaciers did not reach the

Badlands, they did change the river drainage pattern of the continent. Prior to these “ice ages”, the major 

river systems that drained the mid continent flowed northward into Hudson Bay. As the continental glacier 

formed, large lakes developed along the southern boundary of the ice sheets (the modern Great Lakes,

although analogous, are tiny by comparison). These lakes eventually filled to capacity and then poured over 

divides, spilling southward into the Mississippi River valley. The modern Missouri and Ohio Rivers 

7 

 
basically follow the southern boundary of the last great continental ice sheet that melted away about 15,000

years ago. 

Stratigraphy and Geologic Structures in the North Unit 

Geologic Structures 

In most areas around Badlands National Park the bedrock consists of flat lying (or nearly flat lying)

sedimentary strata (see figs. 7 and 8). Faults in the park area typically only display measurable offsets in

the range of several meters. In the North Unit of the park a large northwest-to-southeast-trending system of 

folds and faults defines one of the region’s more prominent structures, the Sage Creek anticline/fault 

system (SCAFS). In some places the SCAFS consists only of a fault, in other places it consists of both folds

and faults, some of which diverge from the overall trend in the system. The eastern end of SCAFS begins in

the vicinity of the Big Badlands (in the eastern end of the North Unit) and is partly be responsible for the 

south-facing Badlands escarpment in that region. The anticline is perhaps most visible in the vicinity of the 

upper drainages of Conata Creek along the Badlands Loop Road (see below). The SCAFS basically

parallels the Sage Rim Road in the western part of the North Unit. South and west of the Wilderness 

Access Trailhead area, the SCAFS forms the north limb of a gently southward-dipping monocline that

essentially flattens into horizontal bedding south of the East Fork of Sage Creek. The SCAFS looses its

surficial expression west of Sage Creek.

8 

 
Composite Stratigraphic Section 

9 

 
Some fault offset that might be associated with the SCAFS is probably related to more recent deep-seated 

slumping along the escarpments. However, Tertiary and older movement histories can be established where

faults and folds display evidence of truncation by erosion (forming angular unconformities) or

contemporaneous movement during deposition. Figs. 9 to 13 illustrate structures in Badlands’ North Unit. 

10 

 
11 

 
Cretaceous Geology of Badlands National Park 

Sedimentary rocks of Late Cretaceous age are

exposed along the lower stream drainages in

several areas within Badlands National Park. 

Cretaceous-age sedimentary materials are 

exposed along the drainages of the Sage Creek 

watershed in the North Unit and throughout the 

Sage Creek Wilderness Area (fig. 14). Less

extensive outcrop areas occur in the Conata 

Creek drainage area near Dillon Pass, and along 

Cedar Creek in the park’s South Unit. The 

Cretaceous rocks are of marine origin whereas 

the overlying Tertiary White River beds are 

terrestrial deposits. The physical and 

geochemical differences between these rock

groups have far-reaching impact on the modern 

environment in the park. Compared with the 

overlying sediments of the White River beds, the 

marine Cretaceous rocks break down relatively slowly, yet produce soils that are both rich in nutrients and 

hold moisture. As a result, areas underlain by Cretaceous bedrock tend to be heavily exploited by plants 

well adapted to the high western prairie. 

The Cretaceous section in Badlands National Park preserves a history of gradual changes in sea level in the 

Western Interior Seaway. It also preserves a record of evolution of marine species and environmental

changes. Two named rock formations represent the Cretaceous stratigraphic sequence in the park: the 

Pierre Shale and the Fox Hills Formation. The oldest Cretaceous rocks exposed in the park consist of 

marine mudrocks deposited about 75 million years ago (during the later Campanian and Maestrichtian 

Epochs of the Cretaceous Period). Marine conditions remained in the Badlands region for an additional 10 

million years. The Late Cretaceous was a time when geologic and environmental changes were occurring in

the region and around the globe. The Laramide Orogeny began in this time period, and resulted in the

gradual uplift of the Rocky Mountains. These mountain uplifts (and associated volcanism further to the 

west) poured vast quantities of sediment into the Western Interior Seaway basin. This created a broad

coastal flood plain that progressively spread eastward, filling in around the rising uplifts as they developed

(such as the Black Hills). West of the seaway, the coastal plain supported a subtropical coastal forest 

ecosystem (which included dinosaurs). 

This pattern persisted until a great catastrophe in Earth’s history occurred—at least one great asteroid

struck in the vicinity of the Yucatan Peninsula. This asteroid impact (or impacts) occurred around 65.5 

million years ago and caused global destruction, possibly assisting the extinction of a large percentage of

animal and plant groups including dinosaurs on land, and in the marine world, the ammonites, most marine 

reptiles, and many other marine species. The story of this “mass extinction” is clearly preserved in the 

sedimentary rock sequence in Badlands National Park. The interval in geologic time and in the sedimentary

rock record is referred to as the Cretaceous/Tertiary Boundary (K/T). Although most of the larger, more 

familiar life forms of the Cretaceous were gone, marine or marginally marine conditions persisted in 

portions of the Western Interior of the continent well into the following early portion of the Tertiary Period. 

Resolving Cretaceous Geologic History Through Paleontology 

Fossils and sedimentary features preserved in the mudrocks of the Pierre Shale reveal information about 

conditions in the Western Interior Seaway. At times the Badlands portion of the seaway had a diverse 

marine fauna that lived both in and on the seabed, or swimming above in the water column. When sea level 

was relatively shallow waves and currents caused mixing of the water, allowing oxygen-rich water to

support a rich fauna at the seabed. With an abundant sea-bottom food supply the seaway could also support

12 

 
a large and diverse swimming fauna. Fossil beds that accumulated during these periods of low-standing sea 

level preserve a mix of shelled molluscs (mostly clams and ammonites), arthropods, and rare bones, teeth, 

and scales of fish and swimming reptiles. In addition, traces of burrows and tracks of bottom fauna are 

preserved, demonstrating that many other invertebrates lived in the seabed, but their soft-body parts have 

not been preserved (or found). Most of the shell material in these intervals is fragmented or disarticulated

by bioturbation; some are preserved in concretions (fig. 15). 

At other times, the seaway was either deeper or stagnant, and was 

essentially inhospitable except for organisms adapted to hypoxic 

(oxygen-depleted) conditions, or for swimming organisms that

could survive in a thin zone of habitable oxygenated water near

the surface. In these hypoxic intervals, the shells of ammonites 

are relatively scarce, but where they occur they tend to be more 

complete. In some beds, shell beds provide evidence that massive 

die-offs occurred. Perhaps storms or upwelling events mixed the 

water column, robbing available oxygen and suffocating most of

the organisms. 

Through time, different species migrated into the seaway basin, 

either coming up from the Gulf of Mexico or coming in from the 

north from the Arctic region. The new arrivals either eventually 

disappeared or adapted and became endemic to the seaway. The 

ammonites in the Pierre Shale and Fox Hills Formation provide 

excellent documentation of evolution, competition, and 

environmental change through time. The identifiable differences in ammonite shell morphology through

time, particularly with baculites, provide a basis for mapping and correlating belts of sedimentary rock

where the different species are preserved. Mapping sedimentary rock units by the fossils is the science of

biostratigraphy. A biozone interval is a sequence of sedimentary strata where a particular species first

appears (at the base), flourishes, and then vanishes (at the top). Some species last a long time and change 

very slowly, whereas other appear and disappear quickly. It is the ones that were short-lived—yet abundant

while they lasted—that are most useful for biozone mapping. In the Western Interior region, the ammonites 

have proven to be the most useful for mapping. 

Cretaceous Stratigraphy of Badlands National Park 

The Pierre Shale and Fox Hills Formation are subdivided into more discrete intervals based on fossil range 

zones (biostratigraphy) or by physical rock characteristics (lithostratigraphy). All fossils used in this 

biozonation (listed below in italics on fig. 16) are species of swimming molluscs, mostly ammonites. The 

lithologic names (facies) follow the naming scheme for equivalent named stratigraphic members in the 

Missouri River valley (with exception of the Enning facies, Disturbed Zone, an Unnamed marine facies of

the upper Fox Hills Formation which do not have equivalent units recognized in the Missouri Valley 

region). 

Late Cretaceous molluscs used for biozonation in the park follow the chronology Gill and Cobban (1966)

and with modification after Landman and Waage (1993) and Stoffer et al., (1998). The biozonation

presented in this report is based only on fossils recovered in the park or within close proximity on the 

Buffalo Gap National Grasslands adjacent to the park (additional biozones are recognized in other areas).

Although many other organisms (both invertebrate and vertebrate) could supplement this biozonation, only

species presented here are considered common or significant for correlation purposes. In the future,

additional biostratigraphic definitions will no doubt become available. Ammonites are perhaps the best 

means for correlation because they are relatively common and relatively easy to recognize in the field, and 

they vary considerably in form through the stratigraphic section allows this separation into unique species 

at different levels in the section. 

13 

 
All specimens illustrated presented below were found in the vicinity of Badlands National Park (including

the Buffalo Gap National Grasslands and private lands surrounding the park). Representative fossil 

specimens from within Badlands National Park were collected under provisions of a NPS collecting permit. 

All specimens present here are in the repository collections of the Department of Invertebrates of the

American Museum of Natural History in New York City or are currently on display at the USGS in Menlo

Park California. 

Pierre Shale 

Only the upper portion of the Pierre Shale is exposed within Badlands National Park. The age of strata in 

the park spans the Late Cretaceous period from the Late Campanian (about 74 million years) through the 

Early Maestrichtian (about 69 million years). In the northern portions of the park region, the Fox Hills 

Formation (Early to Late Maestrichtian) overlies the Pierre Shale. In the Missouri Valley region the Pierre 

Shale is subdivided into members including from oldest to youngest: DeGrey Member, Verendrye Member, 

Virgin Creek Member, Mobridge Member, and Elk Butte Member. Member subdivisions for the Pierre 

Shale have not been recognized north and west of the Black Hills; subdivisions of the Pierre Shale have not 

been previously established for Badlands National Park. However, the term “facies” is used here to 

designate similar stratigraphic subdivisions that are recognizable in the park that share similarities with the 

formally named members in the Pierre Shale in the Missouri River valley region. Descriptions of each of

the member “facies” and corresponding ammonite range fossil zones are described below. 

14 

 
History of Pierre Shale Nomenclature 

The stratigraphic nomenclature of the Pierre Shale has changed over time. Meek and Hayden (1854)

originally assigned the name “Formation no. 4 of the Cretaceous” while mapping the Nebraska Territory

(which then included the Dakotas, Wyoming, and Montana). They later established the name “Fort Pierre

group” (Meek and Hayden, 1861). Their early reports established that the “Fort Pierre” shale includes all 

strata between the gray marl of the Niobrara Formation (exposed along the Missouri River near the South

Dakota-Nebraska border) and the overlying Fox Hills Formation (found in the highest hilltops along the 

Missouri River valley in the north central South Dakota region). Meek and Hayden (1861) extended the 

name “Pierre” across the region to include the Badlands National Park region (where they investigated the 

shale exposures along Sage Creek area while exploring the White River badlands; see fig. 17). Fort Pierre

was along the Missouri River in what is now Pierre, the state capital of South Dakota. Darton (1896)

shortened the name to “Pierre Shale”. 

Searight (1937) established member subdivisions 

for identifiable lithologies within the Pierre Shale 

along the Missouri River valley in South Dakota.

Since Searight’s original report there have been 

many recommended revisions to the stratigraphic 

nomenclature for the Pierre Shale, but most apply 

only to the lower portion of the Pierre (below the 

DeGrey Member) [Agnew and Tychsen, 1965]. The 

name, Monument Hill Member, was applied to the 

upper portion of the Pierre Shale (DeGrey Memberequivalent and higher) around the northern and

western flanks of the Black Hills by Rubey (1930), 

but this member name was later abandoned by Gill 

and Cobban, 1966 (who included equivalent strata 

into portions of the Lower and Upper unnamed 

shale members of the Pierre Shale in that region). 

Crandall (1958) redefined and clarified definitions

for the named members of the Pierre Shale along 

ntologic and lithologic detail to stratigraphic units.

However, Gill and Cobban (1966) established a reliable ammonite-based biozonation scheme for the Pierr

Shale that is recognized as an effective means of correlation across the region. 

the Missouri River valley and provided additional paleo

e

Although the name, Pierre Shale, was established for South Dakota, the name has been loosely applied 

lly

DeGrey Facies 

Only the highest portion of the DeGrey Member (facies) may be exposed in the lower Cedar Creek 

posed 

k

nite, 

facies and in even greater abundance in the overlying Verendrye facies. 

across the entire Western Interior region today (ranging from Texas to Alberta). The name is also forma

established for equivalent-age strata in the north in North Dakota, east of the Colorado Rockies, and in the 

Powder River Basin region of Wyoming. In Montana equivalent latest Campanian- and Maestrichtian-age 

strata are called the Bearpaw Shale. 

drainage along the western side of the Badlands’ South Unit. Although this unit is not completely ex

in the park, fossil material from this member has been found in lag deposits higher in the stratigraphic 

section. In the park vicinity, this unit crops out along the Cheyenne River Valley and along Indian Cree

west of Scenic. In outcrop, the DeGrey facies is typically dark, reddish-gray, fissile shale with thin yellow

bentonite (jarosite) beds. It contains red-weathering siderite concretions that are typically barren or contain

inoceramid clams. Most other fossils are scarce. Diagnostic fossils the DeGrey Member include the 

strangely coiled ammonite, Didymoceras cheyennense (fig. 18) and the fragile, straight-shelled ammo

Baculites corregatus (fig. 19). In the park region, the large clam Inoceramus sagensis occurs in the DeGrey

15 

 
The thickness of the DeGrey facies is undetermined in that the lower boundary of the member with not

been determined within the Badlands region. However, it probably is similar in thickness to exposures 

along the Missouri River (where it is approximately 30 meters thick in the vicinity of Pierre, South 

g 

or the DeGrey Member in a cut bank along the 

Missouri River southeast of the settlement of DeGrey in Hughes County, South Dakota. The noncalcareous, 

Dakota). Accessible exposures to DeGrey facies are located along Highway 44 northwest of Scenic alon

the hillsides of Rapid Creek in section 12, T2S, R12E. 

Crandall (1950) established the name DeGrey Member for units earlier assigned to the “Agency-Oacoma 

bed” of Gries (1942). Crandall established a Type area f

bentonitic shale beds of the DeGrey Member overlie the calcareous marl of the Crow Creek Member. The

Crow Creek Member has not been identified in the Badlands region. 

16 

 
Verendrye Facies 

V.F. Searight (1937) established the Verendrye Member as a gray shale interval with abundant limestone 

concretions between what is now the DeGrey Member (below) and the overlying bentonitic shale beds of 

the Virgin Creek Member. The Type area for the Verendrye Member is beneath the Verendrye Monument 

at Fort Pierre, Stanley County, South Dakota. The Verendrye Member can also be defined by biozonation,

particularly by three ammonite species: Baculites compressus, Baculites cuneatus, and Baculites reesidei

(figs. 22 to 24). However, the Verendrye is also recognizable by a common species of giant clam, 

Inoceramus sagensis that occur in large gray concretions (fig. 25). The Meek and Hayden Survey of the

late 1850’s observed these fossils in the area and named the fossil after Sage Creek. 

In the North Unit, the Verendrye is exposed only along Sage Creek from the vicinity of the campground

northward to the park boundary here it reaches its maximum thickness of about 15 meters in the vicinity of

the Sage Creek bridge near the campground. 

17 

 
The Verendrye facies is also partially exposed along Cedar Creek in the South Unit. The member consists

of medium-to-dark gray, fissile shale and bears an abundance of limestone concretions that range up to 

about a meter in diameter (figs. 20 and 21). Most concretions are septarian and are barren of fossils, but

many display fossil hash or preserve the mostly broken shells of a variety of marine invertebrates and an

abundance of bioturbation structures. Within the park, the top of the member contains the greatest 

abundance of concretions, most of which display heavy septarian-fractures. 

 

18 

 
19 

 
20 

 
The Campanian-Maestrichtian Boundary Unconformity 

An unconformable surface locally defines a boundary between the Verendrye facies and the overlying 

Virgin Creek facies in the park region. This unconformity is recognizable by a sharp change in lithology 

(the underlying Verendrye is much darker) and in some exposures by the preservation of a weathered soil

horizon (illustrated below with an exposure along South Fork of Sage Creek, about a mile south of the Sage

Creek Campground; fig. 26). Elsewhere shell and rock lag deposits bearing reworked materials (including

fossils and concretions) occur along this unconformity. Based on correlation to similar stratigraphic section 

in the region, throughout the United States, and around the world, this unconformable surface represents 

the Campanian-Maestrichtian stage boundary (between the last two epochs of the Late Cretaceous). The

origin is an inferred fall and rise in global sea level. Many species that existed in the Campanian strata are 

not found above the boundary, which suggests that significant ecological changes occurred during this

transitional period roughly between 72 and 71 million years ago (Stoffer, 1998). 

21 

 
Virgin Creek Facies 

V.F. Searight (1937) designated a section of shale bearing numerous thin, yellowish bentonite beds as the 

Virgin Creek Member (after a creek with that name located near the now abandoned community of 

Promise, Dewey County South Dakota. In the North Unit, this unit crops out throughout the middle hillside 

slopes throughout the Sage Creek Valley including the lower drainage basins of East Fork and Middle

Fork, and most of South Fork. The lower part of the member displays an abundance of thin bentonite layers 

or intermittent stringers that occur interbedded within medium gray shale (fig. 27). The lower part of this 

member displays an abundance of limestone concretions that typically developed within or adjacent to

bentonite beds. Within the base of the unit, some concretions preserve intraclasts (ripped up mud chips). 

Fossils are generally scarce within the lower bentonite-rich portion of the member. Specimens of the 

indicator fossil for the Virgin Creek Member, Baculites grandis, are not uncommon in the upper portion of

the member. By comparison to the underlying Verendrye Member, the color of the shale is a lighter gray to 

a greenish-brown or olive color. The Virgin Creek Member is about 20 meters thick north of the Sage Rim

Road, but grows progressively thinner to about 10 meters along South Fork. 

Two older ammonites occur in the lower Virgin Creek facies (Baculites eliasi [fig. 28] and Baculites 

baculus [fig. 29]), but neither of these species is common in Badlands area, and the Baculites eliasi Zone 

may be entirely missing due to the unconformity at the base of the member. The abundance of bentonite

beds and the widespread occurrence of a common ammonite, Baculites grandis (fig. 30), make the Virgin 

Creek Member easy to recognize throughout the region. 

22 

 
23 

 
24 

 
Mobridge Facies 

W.V. Searight (1937) applied the name Mobridge Member to a 25 to 50 meter thick interval of calcareous 

shale, chalk, and marl in the upper Pierre Shale distributed along the upper hillsides all along the Missouri 

River Valley in South Dakota. A Type locality was established adjacent to the historic (now missing)

Missouri River highway bridge at the town of Mobridge, South Dakota. 

Intermittent layers of concretionary limestone define the occurrence of the Mobridge facies in the park

region (fig. 31). In addition, the large, straight-shelled ammonite, Baculites clinolobatus, is relatively 

abundant in the Mobridge facies everywhere it occurs (fig. 32). The Mobridge facies is highly calcareous

relative to the overlying siliceous shale of the Elk Butte facies. 

The Mobridge facies is best exposed along the upper hillsides along the South Fork and Middle Fork

valleys in the Sage Creek Wilderness Area in Badlands’ North Unit. The higher calcareous content of the 

Mobridge facies makes it more resistant to erosion than the underlying and overlying strata. In unweathered

exposures, the unit is a light bluish-gray color. It appears to have a gradational contact with the underlying

Virgin Creek facies. In the best exposures along the South Fork of Sage Creek, the Mobridge Member is

only about 5 meters thick. It grows progressively thicker to the north except in the vicinity of the Sage

Creek Anticline where it is thin or missing, poorly exposed, or is heavily weathered beyond recognition.

Near Wasta, South Dakota, the Mobridge interval—defined by its indicator species, Baculites 

clinolobatus—approaches 15 meters in thickness. The upper Mobridge facies displays an abundance of 

large limestone concretions that in some locations merge to form continuous micritic limestone ledges. The 

contact with the overlying strata is very poorly exposed except along South Fork where it appears 

unconformable beneath undifferentiated Fox Hills Formation.

25 

 
26 

 
Elk Butte Facies 

W.V. Searight (1937) established the Elk Butte Member of the top portion of the Pierre Shale. Unlike the 

underlying Mobridge Member, the Elk Butte is noncalcareous. In the Type area on Rattlesnake Butte in

Corson County, South Dakota, the Elk Butte member is gradational with both the underlying Mobridge and

overlying Fox Hills Formation. Elk Butte facies are recognizable in the park (fig. 33). Because of the 

noncalcareous character of the shale, shell fossils are rare. In the lower part of the Elk Butte facies, a small, 

unnamed species of baculite is fairly common (fig. 34). In addition, the coiled ammonites, Hoploscaphites 

melloi (fig. 35) and Hoploscaphites birkelundi (fig. 36) have been recovered from this interval throughout 

the park region. In northwestern South Dakota and in Wyoming, Hoploscaphites birkelundi occurs in

sandstone facies of the Fox Hills Formation, whereas in the Badlands region and along the Missouri River

valley this species is found in Pierre Shale (Elk Butte facies). 

The designation as Elk Butte Member in Badlands National Park is based on fossils and lithologic 

appearance and stratigraphic position (similar to exposures in the Missouri River Valley region). In contrast 

to the Missouri Valley region, the Fox Hills rests on an unconformable surface on the Elk Butte and older 

units in the Badlands region. In the area, the thickness of the Elk Butte is highly variable ranging form

nearly 50 meters along the White River south of Kadoka, to possibly missing along the crest of an anticline 

in the southern Sage Creek Wilderness Area where the Fox Hills rest unconformably on the Mobridge

Member. These unconformable relations, particularly across the crest of anticlines, demonstrate that

Laramide tectonism was actively occurring in the Badlands region while marine sediments were being 

deposited in the Late Cretaceous. 

Elk Butte facies (bearing Hoploscaphites melloi) occurs along the upper tributaries of East Fork along the 

southern side of the Sage Creek Anticline in the Grassy Table Overlook area. It also occurs at creek level in 

the core of the Sage Creek Anticline in the Dillon Pass/Conata Creek Basin area. In these areas, shale 

exposed along creek level is very dark-gray and fissile, and contain large, barren, light-gray colored

concretions that lack fossils. 

27 

 
28 

 
29 

 
Fox Hills Formation 

Meek and Hayden (1862) identified the Fox Hills Formation (Formation No. 5 of the Cretaceous) to 

encompass the interval between the underlying Pierre Shale and the overlying Tertiary Fort Union Group.

They described the interval as being widespread, ranging from the Fox Hills (along the Moreau River, a 

tributary of the Missouri River) to as far was as the eastern flank of the Bighorn Mountains and along both

the North and South Platte Rivers (Agnew and Tychsen, 1965). The Fox Hills is now recognized as a 

complex series of Maestrichtian-age sedimentary facies (marine, transitional, and terrestrial) that interfinger 

across the Western Interior region, with detailed relationships largely unresolved across the region. The 

complexity of the Fox Hills is demonstrated with ammonite biozonation, particularly where different

ammonite range zones are known to cross various lithologic facies. For instance, Robinson and others 

(1959) demonstrate that the ammonite range zones of the Pierre Shale starting with Baculites eliasi and

higher occur in sandy lithology assigned to the Fox Hills Formation along the northern flank of the Black

Hills. Conversely, the youngest ammonite species associated with sandy lithofacies of the Fox Hills 

Formation along the Grand River in northern South Dakota occur in Elk Butte shale lithofacies in southern

South Dakota. 

The most thoroughly investigated exposures of the Fox Hills Formation are in northern South Dakota along

the Grand River valley where highly fossiliferous units have been the targets of many paleontological 

investigations. Karl Waage (1968) formally established a Type designation to that region and assigned 

members based on both lithologic and paleontological content. Because the lithology of the Fox Hills 

varies considerably across the region, only the paleontological content is truly suitable for correlation.

Waage named four members of the Fox Hills Formation, and only the two lowest members in the Type area 

contain abundant fossils, the Trail City Member (lower) and the Timber Lake Member (middle). Two upper

terrestrial units include the Colgate Member and Iron Lightning Member. How these different members 

correlate across the region is not clear. The descriptive differences between Fox Hills Formation and Hell 

Creek Formation in South Dakota are quite muddled. The most simplistic lithologic breakdown seems to be 

recognizable as follows: if it is shale and has marine fossils it is Pierre Shale; if it is sandy and contains

marine fossils then it is Fox Hills; and if it is of terrestrial origin and contains plant material and (or) 

dinosaur bone then it is Hell Creek. However, these rules are rarely recognized. The different facies were 

likely deposited concurrently in different parts of the region.

A generalized regional correlation for the Fox Hills and other stratigraphic units are shown below (fig 37). 

The eastern Wyoming section follows a Type description by Gill and Cobban (1966). However, Pettijohn

(1967) established a type area for the Hills Formation in the region around the town of Faith, South Dakota 

in the northwestern portion of the state. In addition, Karl Waage (1968) established a type description of the 

Fox Hills in the Grand River Valley region in the northern Missouri River Valley of South Dakota. 

Confusion remains relating to the inferred position and relative ages of units described as “Hell Creek

Formation” throughout the Western Interior region. Dinosaur bearing beds are included in the White Owl 

and Stoneville Coal facies by Pettijohn (1967). Whether these units are equivalent to dinosaur bearing

strata of the Hell Creek elsewhere in the region is unresolved. However, correlation of the Badlands section 

presented here basically follows terminology of both the northwestern South Dakota and Missouri Valley 

sections (following descriptions by Pettijohn and Waage). 

According to Gill and Cobban (1973) the Fox Hills represents shallow marine, marginal, and terrestrial

deltaic facies that prograded eastward from the Montana/Wyoming boarder region. Units such as the upper 

Timber Lake Member in the Type area of South Dakota and in eastern Wyoming consist of a massive 

cross-bedded sandstone sequence. The lack of equivalent sandstone facies in the Badlands area suggests

that either the units are missing (due to erosion) or that progressive uplift of the Black Hills, the Chadron

Arch, and other structural elements including the Sage Creek Arch (or anticline) may have prevented an

influx of sediment into the Badlands region during Early to Late Maestrichtian time. It is likely that both

theories may apply. 

30 

 
The Fox Hills Formation in the Badlands National Park region is unlike exposures of the formation in

Wyoming or in its Type area in the northern Missouri River Valley region of South Dakota, and is therefore

undifferentiated in the park area. However, characteristics of the Badlands’ Fox Hills share some

similarities with other areas, particularly its fossil content. Because of these similarities, the geologic story 

revealed by strata exposed in Badlands National Park can be interpreted.

In general, sandy facies of the Fox Hills Formation is thin or missing along the eastern flank of the Black

Hills and is difficult to resolve in the Badlands region. Strata that better fits a lithologic description of Fox 

Hills (rather than Pierre Shale) occurs as thin ledge-forming sandstone beds that cap the hilltops throughout

the southern Sage Creek Wilderness area (especially along the South and Middle Forks of Sage Creek. In

the hilltops around the Sage Creek Campground, large, brown weathering, ironstone concretions crop out 

amongst sandy mudstone and shale. These upper units of Cretaceous section have been heavily altered by 

meteoric exposure prior to deposition of the basal Chadron Formation (alteration by pedogenesis associated

with the Yellow Mounds and Interior paleosols). However, in this weathered interval, casts of fossils, 

arthropod parts, fossil wood, and rare sharks teeth occur. 

East of the Sage Creek Campground area in the vicinity of White Butte, a moderately irregular 

unconformable surface is preserved beneath sediments that appear to fill channels carved into the upper 

Pierre Shale along the crest of the Sage Creek Anticline. A brown, ledge-forming hardpan has developed 

intermittently along this surface. It can be traced throughout the hilltops along the valleys of the Middle and 

South Forks of Sage Creek (fig. 38). Specimens of the ammonite, Hoploscaphites melloi (a fossil known

from the Elk Butte Member in the Missouri River valley), were recovered from below this boundary. 

Fossils typical of the Trail City Member (of the Missouri Valley region) were observed above this layer. In

the Type area for the Fox Hills, the coiled ammonite, Hoploscaphites nicolletii occur locally in abundance 

in the Trail City Member (fig. 39). Although no specimens of this species have been found in the park, 

examples have been recovered from along the Cheyenne River valley north of the park. 

31 

 
Higher in the section, the sediment color fades from pale gray to buff and brown colors, and beds of large, 

reddish brown, fine-sandy textured concretions occur. These concretions commonly merge to form a 

bench-like surface along hillsides throughout the park area (fig. 40). Amongst the red concretions

specimens of Jeletzkeytes nebrascensis have been recovered. This species is an index fossil for the Timber 

Lake Member of the Type Fox Hills in the Missouri Valley region (Landman and Waage, 1993). It is also

the youngest ammonite zone fossil of the Late Cretaceous (Kennedy and others, 1998). 

Above the concretionary sandstone is an interval of green- and red-colored fossiliferous marl that yields

ammonites, belemnites, fish remains, plant material, tiny clams, oyster fragments, and other material (fig.

41). Pettijohn (1967) described belemnites and other marine fauna in his Enning facies at the top of the Fox

Hills in northern South Dakota. 

Ammonites from this interval have been identified as Jeletzkeytes nebrascensis (fig. 42). However,

belemnites (Belemnitella bulbosa) are perhaps the most common fossil from this interval (fig. 43). 

Belemnites are also known from the Timber Lake Member in the Missouri Valley region. Also, Jeletzkeytes 

nebrascensis is known from the Breien Member of the Hell Creek Formation in southern North Dakota

along the Missouri River valley. In Badlands National Park, this interval (Enning facies) only occurs in 

32 

 
scattered outcrops along the northern park boundary and north of the park. To the south this interval is not

preserved or exposed beneath the White River beds. 

Stoffer and others (2001) gave the name Disturbed Zone to a widely distributed interval of soft-sediment 

deformation above the Enning facies interval throughout the park area (see discussion below). The 

Disturbed Zone is overlain by as much as 16 meters of alternating sand and shale beds. The maximum

thickness of this interval in the park is near the Grassy Tables Overlook in the North Unit. The top of this 

section grades upward and vanishes into the overlying Yellow Mounds weathering profile. The Disturbed 

Zone defines the extinction boundary for most Cretaceous species in the park region. 

33 

 
Although belemnites have been reported from many units in the Pierre Shale throughout the Western 

Interior region, the only reported occurrence of belemnites in the park and vicinity is from the upper 

Timber Lake and Enning facies of the Fox Hills Formation. Pettijohn (1967) described belemnites from his 

“Enning facies” in his original description of the Fox Hills section in northwestern South Dakota. The 

Enning facies consists of marine shale and marl beds (bearing belemnites, oysters, and other marine fauna) 

and represents a marine incursion during the Late Maestrichtian. In Pettijohn’s study area, these marine

shales overlie terrestrial sandstone units bearing dinosaur fossils. This underlying dinosaur-bearing strata is 

included in “Hell Creek Formation” in most of the literature about the northwestern South Dakota region. 

However, no dinosaur bearing beds are been found in the park region. 

Strontium isotope geochronology data derived from belemnites recovered from the Enning facies in

Badlands National Park have yielded age values of latest Maestrichtian age. 87Sr/

86Sr sample values derived 

from Enning facies belemnites range from 0.707801 to 0.707821 (Stoffer and others, 2001). Dennis Terry

(personal communication, 2002) reevaluated this belemnite data using revised 87Sr/86Sr geochronology data

presented by McArthur and others (1998) and came up with an age of 66.3 million years (within a 95

percent confidence interval). This age determination is fundamental to the interpretation that the Disturbed 

Zone in the Badlands National Park region is associated with the Cretaceous-Tertiary boundary. 

34 

 
The Cretaceous-Tertiary Boundary Interval in 

Badlands National Park

A possible Cretaceous-Tertiary (K-T) boundary interval has been recognized in marine strata in Badlands 

National Park. The boundary is associated with a widespread unit displaying soft-sediment deformation

(0.5 to 4 m thick) called the Disturbed Zone (Stoffer and others, 2001; Terry and others, 2001). This bed is

within a thicker interval historically described as the Interior zone (Raymond and King, 1976). In

historical usage, the Interior Zone encompasses all a brightly colored series of beds that falls between gray 

marine mudrocks of the Pierre Shale and the base of the White River beds (fig. 44).

The Interior Zone within the North Unit of Badlands National Park is now subdivided into a series of 

identifiable units based on fossil content and lithologic characteristics (fig. 45). In the North Unit of the 

park, the majority of the parent rock for the Interior zone is now assigned to the Fox Hills Formation and a 

series of sediments and fossil soil horizons (paleosols). All Fox Hills and younger units are variable in their 

thickness, composition, and appearance across the park region. In particular, sandstone facies thin and

vanish southward across the park region. 

35 

 
A Historical Perspective on the Interior Zone 

The Interior zone has a long history of debate and discovery. In the days when the Badlands region was still 

part of the Nebraska Territory, the Nebraska Geological Survey used the name “Rusty member of the 

Pierre” for the brightly colored interval between the gray mudrocks of the Pierre Shale and the base of the 

overlying White River beds. This was in recognition that the interval displayed evidence of heavy 

weathering or leaching prior to deposition of the sediments of the Chadron Formation. Interpretation of the 

interval was delayed by the general lack of identifiable fossils. 

Freeman Ward (1922) first used the name “Interior phase of the Pierre” to describe the brightly colored

sequence of beds west of Interior, South Dakota. Later, Ward (1926) concluded that the Interior beds were 

in part equivalent to Fox Hills Formation. 

Meanwhile, H.R. Wanless (1923) recognized that the Interior Zone also represented an interval of 

weathering and leaching, and that the upper surface of the Interior interval was irregular beneath the base of 

the overlying Chadron Formation of the White River Group. Much later, R. J. Dunham (1961)

demonstrated that on a regional scale the weathered surface on the Pierre Shale in the Badlands region 

formed on surfaces that ranged as far down in the section as the Niobrara formation and up section to

overlie Eocene sediments. He concluded that the surface was of Eocene age. Pettijohn (1966) expanded this 

investigation across the region and demonstrated that what he named the “Yellow Mounds weathering

profile” was of Late Eocene age and could be found imprinted on sediments ranging in age from Late

Cretaceous to middle Eocene. He name the Yellow Mounds after a series of small yellow mounds resting 

on Fox Hills Formation in the vicinity of the Wilderness Access trail head in the Badlands North Unit (fig. 

46). 

Retallack (1983) also investigated the Interior zone while investigating ancient soil profiles in the White 

River Group. He concluded that a series of paleosols and channel sandstones were established on an

irregular surface of Pierre Shale and possibly Fox Hills, but added that a sandy unit below the base of the 

Chadron may be equivalent to the Slim Buttes Formation (an Eocene unit in northwestern South Dakota). 

Following Pettijohn’s weathering profile interpretation, Retallack used the name “Yellow Mounds” to 

describe an older weathering profile below the “Slim Buttes” unit, and limited the name “Interior” to the 

red fossil soil profile developed on top of this bed. 

Terry and Evans (1994) later established that stream channel and flood plain deposits are locally preserved 

beneath the base of the Chadron Formation and that these deposits are crosscut by incising channels at the 

base of Chadron Formation. Terry also identified an Eocene mammal tooth within the unit and concluded

that some of the sediments were derived from the Black Hills region. He assigned the name Chamberlain

Pass Formation to flood plain and stream channel sediments overlying the Yellow Mound Surface and 

below and including the Interior paleosol. 

Establishing the age of youngest identifiable species in the original sediments imprinted by Yellow Mounds

weathering profile is an ongoing task. Gill and Cobban (1966) and Landman and Waage (1993) established

ammonite biozonation for the Pierre Shale and Fox Hills Formation in the region. Stoffer (1998) correlated

36 

 
many of these ammonite biozones to the park area. Evaluating sedimentation rates based on established 

ammonite ages, Stoffer and others (1998) concluded that the stratigraphic section of the upper Pierre ShaleFox Hills interval in the northern park region was too thick not to consider that some of the upper section

beneath the Yellow Mounds may be Paleocene in age. However, the possibility that the park section 

encompassed the Cretaceous-Tertiary boundary wasn’t possible until belemnite fossils were discovered and 

dated using strontium-isotope geochronology. These fossils yield ages that ranged upward into the Late 

Maestrichtian. These belemnites were recovered from sediments immediately below a zone of widespread

soft-sediment deformation (the Disturbed Zone). Initial investigations suggest that this interval may be

associated with the terminal Cretaceous asteroid impact, or impacts (Stoffer and others, 1997; 2001). In the 

park and above the Disturbed Zone are a maximum of 16 m of drab-colored marine sediments beneath the 

Yellow Mounds interval. This interval is designated the name Unnamed marine facies of the Fox Hills 

Formation. This interval increases in thickness north of the park. 

The Disturbed Zone 

The Disturbed Zone (DZ) is a zone of soft-sediment deformation occurring throughout the northern

Badlands National Park region. Stoffer and other (1997) first described the interval as a buried slump 

horizon in the upper Pierre Shale along the crest of the Sage Creek Anticline. However, additional 

investigations by Stoffer and others (2001) demonstrated that the Disturbed Zone is a relatively continuous

stratigraphic unit throughout the region ranging in thickness between several meters to less than a meter. 

This discussion provides a description of the DZ along with basic evidence that suggests the origin of the 

deposit corresponds with a widespread natural catastrophe that drastically changed environmental and 

ecological conditions in the Western Interior Seaway region. Whether this deposit is a result of a great 

asteroid impact associated with the Cretaceous-Tertiary boundary will no doubt be discussed for 

generations. A map showing the location of selected DZ localities is shown in fig. 47. 

Supporting evidence that the DZ represents the K-T boundary includes petrography data, 

magnetostratigraphy, sequence stratigraphy, and paleontological analyses (see Stoffer and others, 2001). 

However, perhaps the best physical evidence is easily seen on outcrops in the field. Highlights of the 

evidence includes: 

37 

 
A rich, diverse Late Cretaceous marine fauna occurs below the DZ (including ammonites, 

belemnites, mosasaurs, and inoceramids). No fossil remains of these organisms have been

recovered from sediments above the DZ. 

The DZ is mappable throughout the northern portion of the park across a region at least 25 km

wide and extends north of the park at least 30 km, and perhaps further. The bed is a result of

widespread displacement of seabed sediments across the region. 

Up to 16 m of drab-colored marine beds (alternating sand and shale beds) occur in the thickest

section preserved above the DZ. The interval is rich in trace fossils, but has not yielded Cretaceous 

fauna. The identified fossils and traces in this upper interval all have modern descendents (such as 

barracuda, sharks, oysters, sand fleas, etc.). 

All DZ outcrops display oriented roll structures (sediment layers that were rolled up like a carpet 

while they were still soft and pliable). 

All roll structures display an east-to-west orientation in outcrop (indicating that sediment

movement was toward the south). 

The interval ranges in thickness between about half of a meter to as much as 4 meters wherever it 

is exposed (average about 1 m). 

Other soft-sediment features include clastic dikes, slump glide-plane surfaces, and dewatering

structures, none of which penetrate the beds above or below the DZ. 

The DZ locally contains charcoal and fragmented plant material. 

The sediments above the DZ are flat lying and conformable along a scoured surface. These 

sediments preserve an abundance of small trace fossils by marine organisms, but the sand and 

shale beds are not highly bioturbated like the sediments below the DZ. Deep, pervasive 

bioturbation ended with the event responsible for deposition of the DZ. 

The DZ is unique; there are no other examples of other beds or units displaying widespread softsediment-style disruption anywhere else in the exposed stratigraphic section of the Cretaceous or 

Tertiary in the park region.

The DZ represents a change in depositional conditions in the region. This evidence presented above

suggests that the DZ represents the Cretaceous-Tertiary extinction boundary. It is important to emphasize 

that the sediments both below and above the DZ are marine in origin (see discussion about Unnamed 

marine facies of the upper Fox Hills Formation below). The preservation of bedding structures above the 

DZ indicate that a significant crash in the bioturbating seabed fauna occur across the interval. However, the 

variety of traces preserved in the sand sheets above the zone indicates that small, bioturbating organisms 

gradually recolonized a shallow marine seabed. 

The character and distribution sedimentary features within the DZ indicate that a catastrophic event is

associated with its origin. The mix of materials in the DZ show that transport of material occurred with the 

direction of movement toward the south. The volume of material separated from the seabed is in the range

of a meter. Morton (1988) described a similar magnitude of soft sediment deformation caused by a Class 5 

hurricane (as Hurricane Camille impacted the sea bed in the gulf region). Similar impacts occur from large 

tsunamis along coastal regions. However, the disruption across such a large region within the Western

Interior Seaway suggests that something possibly larger that a storm or earthquake was responsible for

formation of the DZ. 

38 

 
Conata Creek Locality 

The Disturbed Zone (DZ) is exposed in the headwaters region of Conata Creek where the stream has 

exposed the “Interior zone” along the Crest of the Sage Creek Anticline. The DZ is visible from the 

Badlands Loop Road at the Rainbow Colors Overlook site, but other exposures occur along tributaries 

draining the High Pinnacles area (figs. 48 to 50). 

39 

 
Grassy Tables Overlook Locality 

The Grassy Tables Overlook locality is approximate 3 miles directly west of the Pinnacles Ranger Station

and south of the Sage Rim Road. It is in the vicinity of several brightly colored hills of the “Interior zone” 

in the upper Sage Creek Basin. The thickest section of the Disturbed Zone (DZ) is exposed above creek 

level. It is locally up to 4 m thick. The section above the DZ consists of about 16 meters of drab-colored

marine sediments those grades upward into the Yellow Mounds paleosol. Figs. 51 to 56 illustrate aspects of 

the upper Fox Hills section in the Grassy Tables Overlook locality. 

40 

 
41 

 
Wilderness Access Trailhead Locality 

The Wilderness Access trailhead locality yielded some of the most significant information about the age of 

the deposits (figs. 57 and 58). Specimens of Jeletzkeytes nebrascensis and other fossils were identified 

below the Disturbed Zone (DZ) in this location. In addition samples for paleomagnetism study and 

belemnite samples for isotope geochronology were gathered here (Stoffer and others, 2001). The changes 

in faunal content and bioturbation sedimentation patterns across the DZ in this location provide some of the 

strongest evidence that the DZ represents the Cretaceous-Tertiary boundary. 

42 

 
Buffalo Gap National Grasslands Locality 

Fox Hills Formation exposures along the hilltops east of Sage about a mile north of the park boundary 

preserve a complete sequence encompassing the upper Pierre Shale and Fox Hills Formation that includes 

the Disturbed Zone. Exposures of the Fox Hills on the national grasslands suggest that sediment coloration

in the Fox Hills is original and may not be associated directly with the formation of the Yellow Mounds 

and Interior paleosols that formed later in the Tertiary (fig. 59). East-to-west oriented roll structures 

demonstrate that the Disturbed Zone at this locality is similar to localities in the park (fig. 60). 

43 

 
Dry Creek Locality 

The Disturbed Zone (DZ) crops out along stream level in the headwaters region of Dry Creek in the Sage

Creek Wilderness Area near the park’s southern boundary (fig. 61). 

Unnamed marine facies (upper Fox Hills Formation) 

Sediments overlying the Disturbed Zone preserve evidence that marine conditions persisted in the region. 

The sediments are included in a stratigraphic interval informally named here “Unnamed marine facies of 

the upper Fox Hills Formation.” This interval consists of flat-lying beds of shale and sandstone that locally 

bears an abundance of marine trace fossils, but body fossils (such as shell material and bone) are very 

scarce. No fossils of definitely Cretaceous species have been found in this interval above the Disturbed 

Zone, but fish bone fragments, teeth of a barracuda-like fish, and plant material have been observed. In the 

North Unit the Unnamed marine facies is thickest in the Grassy Tables Overlook locality where at least 27

individual sand sheets (with intervening shale) occur in a 14 m section. The sand sheet range in thickness 

from 1 cm to a maximum of about 15 cm. Elsewhere the Unnamed marine facies are only a few meters 

thick at most, pinch out, or are missing along with the overlying paleosols beneath the base of the Chadron

Formation. The lack of Cretaceous fossils and its location above the Disturbed Zone suggests that these 

sediments may have been deposited in the early Paleocene. The thickest best exposures of this interval in

the park are in the Grassy Tables Overlook locality. 

The sand sheets in the Unnamed marine facies preserve current-ripple bedding and in some cases, an 

abundance of trackways and traces. The types of trace fossils found in the upper marine facies are common 

in habitats ranging from the lower intertidal zone and shallow subtidal zones and can be grouped to

Skolithos/Cruziana ichnofacies. 

Skolithos ichnofacies typically occur in sandy sediments and is characterized by vertical dwelling burrows 

and tubes that extended many centimeters into a soft substrate. Cruziana ichnofacies are characterized by 

simple locomotion traces with some U-shaped dwelling and shallow resting and hiding traces made in soft 

to firm sediments (fig. 62). Both varieties of ichnofacies occur within the intertidal or shallow subtidal 

zone. Specific types of traces found include:

Diplacraterion are a U-shaped trace that typically display two entrance dots on the surface of a bed;

44 

 
Ophiomorphia are branching burrows with either horizontal, oblique, or vertical box-like networks; the

exterior of the burrows are characterized by a “corn cob” or knobby texture formed by an shrimp-like 

animal that packs fecal pellet along the burrow walls; 

Thalassinoides are branching burrows (Y- or T-shaped branches) with horizontal, oblique, and (or) vertical 

chamber-like networks and enlargements at junctions between some branches (the probable trace maker 

was an arthropod) (fig. 63);

Cruziana, crawling traces with a “herringbone” (chevron-like) tracks with ridges defining a medial groove; 

the bi-lobed character is also a result of two parallel furrows created by an arthropod’s legs scratching the 

surface of the sediment. 

45 

 
Tertiary Geology of Badlands National Park 

Nonmarine sedimentary rocks of Tertiary age are collectively assigned to the White River and Arikaree 

Groups in the Western Interior region. These strata range in age from Eocene through early Miocene, with 

Oligocene-age materials of the White River Group dominating the section. The White River beds consist of

sandstone, tuffaceous sandstone, conglomerate, mudrocks (shale and clay mudstone), bone beds, and 

volcanic ash deposits deposited on an ancient floodplain that received sediments shed from uplifts 

throughout the Rocky Mountain region (figs. 64 and 65). 

The different stratigraphic units of the White River beds formed under varying environmental conditions, 

ranging from hot, humid conditions in the early Tertiary when the elevation was still near sea level and

great bodies of water (brackish inland seas and lakes) still existed throughout the Western Interior region

and between the rising mountain ranges of the Rocky Mountains to the west. Through mid Tertiary, the

land gradually rose and river systems evolved. Climatic condition grew progressively dryer and forested

environments gave way to savannah or steppe environments. By the close of the Tertiary, desert-like

conditions influenced depositional processes (particularly aeolian dust) and the fauna adapted to such

conditions. 

46 

 
Historical Overview of the White River Group 

A search in the GeoRef database yields hundreds of citations relating to the Tertiary stratigraphy of the 

Western Interior region. This discussion only touches on the naming of specific stratigraphic units

(summarized by Agnew and Tychsen, 1965), but makes no attempt to review the rich body of knowledge

gained from the study of the Tertiary deposits in the Badlands region. 

F.B. Meek and F.V. Hayden first published on the name “White River” for deposits in the Nebraska 

Territory in 1858. They mention that the oldest member of the sequence is a Titanotherium bed (now

Chadron Formation). Meek and Hayden (1862) recognized that the White River beds were not marine or

brackish marine deposits and that in Wyoming the White River beds overlie Fort Union and Lance beds

(Paleocene) and underlie Loup Fork beds (Pliocene beds). Meek (1876) locally subdivided the White River 

into the Chadron Formation (below) and the Brule Formation (above). J.L. Wortman (1893) applied the

named “Oreodon beds” (lower) and “Protoceras beds” (upper) to be later named the Brule Formation by

Darton (1899). 

Further subdivisions of the formations were made over time. John Clark (1954) subdivided the Chadron 

Formation into three members: Ahearn (lowest), Crazy Johnson (middle), and Peanut Peak (highest). All

three members occur in the vicinity of the park’s South Unit, but only the Peanut Peak Member is 

recognized in the North Unit. 

J.D. Bump (1954) subdivided the Brule Formation into two members: Scenic Member (lower - formerly

“Oreodon beds”) and Poleslide Member (upper - formerly “Protoceras beds”). J.R. McDonald recognized 

that “Miocene-age” strata (Rosebud Formation) overlies the Brule Member and is equivalent in age to

Arikaree Group elsewhere in the region. In the park area, Arikaree age sediments of latest Oligocene age 

were recognized and assigned the name Sharps Formation (Harksen and others, 1961). Nicknish and 

Macdonald (1962) assigned the name Rockyford Ash to a thick widespread volcanic ash deposit that

defines the base of the Sharps Formation. 

Retallack established a type section for the White River and lower Arikaree Groups in Badlands National 

Park in the Pinnacles area of the North Unit (in the headwaters region of Conata Creek). In this section he 

recognized as many as 87 superimposed fossil soils in 143 m of stratigraphic section, including up to 10 

different types of fossil soils in addition to stream channel deposits. Terry and Evans (1994) also

recognized an Eocene channel and floodplain deposit that is older than the base of the Ahearn Member of 

the Chadron, but younger than the Yellow Mounds weathering profile on older marine mudrocks below the

White River Group. 

The Yellow Mounds and Interior Paleosols 

The base of the White River Group rests unconformably on a surface that locally preserves ancient 

weathering profiles. At least two weathering profiles of different ages are now recognized beneath the 

Chadron Formation (fig. 66). The older surface, the Yellow Mounds weathering profile, was recognized by

Pettijohn (1965) to be a regional weathering surface of Eocene age that formed on an eroded surface of 

older formation ranging in age from Late Cretaceous to Eocene. In the Badlands National Park region, the 

Yellow Mounds is imprinted on Fox Hills Formation in the north and east and on Pierre Shale closer to the 

Black Hills. 

47 

 
Retallack (1983) supported the idea that the Yellow Mounds represent a paleosol, or series of paleosols, of

Eocene age. He suggested that the yellow coloration of the Yellow Mounds was a result of meteoric 

weathering of older marine sediments exposed near the surface over a long period of time. In some places 

(such as shown below in fig. 67) the orange-colored sediments of the Yellow Mounds preserve crossstratification (probably stream-channel deposits). 

The distinct coloration of the sediments of these four units (shown in fig. 67) reflects the differing

depositional environments in which they formed. The green beds are unaltered shallow marine sediments 

(bearing trace fossils). The orange “Yellow Mounds” consist of soils and (or) reworked soil, possibly 

associated with mixed brackish and freshwater environments. The red “Interior Paleosol” soil reflects 

higher oxygenating conditions. This is supported by an abundance of fossil termite nests and other burrow

that occur locally throughout the Grassy Tables Overlook exposure belt. Terry and Evans (1994) include 

these floodplain-style deposits in the Chamberlain Pass Formation. 

The red earth of the “Interior-Chamberlain Pass” interval stands out in contrast to the gray floodplain

sediments of the overlying Chadron Formation. In the past, the inferred thickness of the “Yellow Mounds” 

have supported the idea that a great period of time lapsed between erosion and exposure of the older 

Cretaceous sediments and deposition of the basal Chadron Formation. A new interpretation presented here 

is that sedimentation was more continuous, albeit slow, between the times when the Western Interior 

Seaway (or Cannonball Seaway) finally withdrew and when sediments derived from the exposure of the 

core of Laramide mountain ranges began to flood across the Badlands region. Just as changes in eustatic

sea level affected depositional patterns in the sediments of the Western Interior Seaway, global eustatic 

cycles probably also influenced the pattern of stream base level (and consequent deposition and erosion) on

the early Tertiary landscape. Backfilling of stream valleys occurred during high stands in sea level, and

soil-weathering profiles formed when stream base level fell (associated with a fall in sea level). The pattern 

of coloration typical of the terrestrial deposits of the White River Group did not come into play possibly

48 

 
until the landscape had finally risen high enough to not be directly linked or influence by global changes in

sea level. 

Chamberlain Pass Formation 

Terry and Evans (1994) gave the name Chamberlain Pass Formation to beds that crop out along an 

unconformable surface between the weathered Pierre Shale (Yellow Mounds) and beneath the base of the 

Chadron Formation (fig. 68). The upper surface of the Chamberlain Pass has a red paleosol overprint (the 

Interior paleosol). It is therefore younger than the Yellow Mounds paleosol, but older than the Interior 

paleosol (after Retallack, 1983). Terry and Evans (1994) recovered a fossil tooth from the gravel and 

established that the age of the deposit was Eocene. 

Chadron Formation 

In Badlands National park poorly consolidated mudrocks of late Eocene age are assigned to the Chadron 

Formation (fig. 69). The formation is named after the town of Chadron, Nebraska where strata equivalent in

age and character crop out. The interval was originally named the Titanotherium beds after an abundance of

bones of large rhinoceros-like mammals were observed and mapped by early investigators. Of the three 

members of the Chadron Formation only the Peanut Peak Member (the youngest member) is recognized in 

the North Unit of Badlands National Park. Portions of the two older members, the Ahearn Member (oldest) 

and Crazy Johnson Member (middle) are preserved in the South Unit region with equivalent strata in

northwestern Nebraska (Terry, 1998). 

The Chadron consists of typically gray to olive-gray sandy clay, but locally preserves conglomerate at its 

base and also preserves white, freshwater limestone lenses, a short distance above the base. The high

bentonitic-clay content turns the weathered surfaces of the Chadron to a slick gumbo when wet that dries to 

a frothy popcorn textures. These characteristics create an inhospitable environment for most vegetation, and

so the Chadron is typically barren throughout it outcrop exposure belt. 

49 

 
Intermittent lenses of coarse gravel (poorly consolidated conglomerate) crop out at along the base of the 

Chadron Formation (fig. 70). The gravel and sand in the formation consist of chert, granitic rocks, and

metamorphic materials probably derived from streams draining the core and surrounding sedimentary

outcrop belts of the Black Hills region and possibly from more distant sources. Some of the chert cobbles 

preserve structures typical of conical algal stromatolites, and are probably Cambrian or Precambrian in age. 

The source of these chert cobbles is unknown.

Freshwater limestone beds (bearing fish and plant remains) occur intermittently in the lower part of the 

Chadron Formation in the North Unit. This limestone forms a cap rock on many buttes throughout the Sage 

Creek Wilderness Area, including White Butte just east of the Sage Creek Campground (fig. 71). The upper

part of the formation consists mostly of a sandy clay mud that weathers to a popcorn gumbo mud. 

The Chadron Formation was originally named the “Titanotherium beds” and was originally assigned to the 

Oligocene Epoch. However, with additional regional correlation and discovery, the Chadron interval is now 

recognized as being latest Eocene in age, with the name “Chadronian” assigned to the last stage of the 

epoch (Terry, D.O., Jr., 1998). Radiometric dates from ash deposits recovered from the lower Chadron

(Ahearn Member) provided and age of 37.2 (+/- .7) million years (Retallack, 1983). Deposition associated

with the Chadron is regarded as being basically “continuous” with the overlying Scenic Member of the 

Brule (of early Oligocene). 

Scientific investigations of fossils and sedimentary deposits have yielded information to support

interpretation of how the landscape may have appeared at the time the materials were deposited. In addition 

to bones, the sediments preserve traces of invertebrate remains, plant materials, root traces, animal burrows,

coprolites, animal tracks, fossil soils, and sedimentary deposits typical stream and floodplain deposits 

(including shallow, warm lakes). The deposits also preserve evidence of the chemical processes associated 

with converting the soft sediments and organic remains to rock, a complex variety of processes collectively

called diagenesis. Understanding depositional environments and diagenetic processes is important to

understanding why fossils may be preserved in one location, but not another. Retallack (1983) provided an 

overview of the variety of fossils recovered over time from the Chadron Formation and overlying Scenic

Member of the Brule. His list includes: 

50 

 
aquatic turtles (Graptemys) 

semi-aquatic rhinoceros (Trigonias), 

cursorial rhinoceros (Hyracodon, Caenopus) 

titanotheres (Menodus) (also rhinoceros-like animals) 

horses (Mesohippus) 

creodont carnivores (Hyaenodon) 

oreodonts (Merycoidodon) 

pig-like entelodon (Archaeotherium) 

Other fossil remains discovered include: alligator, frog, lizard, birds, opossum, small insectivore, rodent, 

saber-tooth cat, tapiroid, peccary, camel, and squirrel-like, deer-like, rabbit-like and fox-like animals, and

others. This community of species is consistent with a forested floodplain with scattered sedge meadows, 

oxbow ponds, and forested upland environments. By Oligocene time, the forested uplands gave way to

dryer savannah-like environments. 

Brule Formation 

The Brule Formation represents stream and floodplain deposit that accumulated during Oligocene Epoch 

(between about 32 and 26 million years ago). The Brule is subdivided into two members. The lower Scenic 

Member conformably overlies the gray mudrock of the Chadron Formation and consists of alternating

rusty-red and grayish white layers of strata. The upper Poleslide Member is dominated by light gray

massive cliff-forming sandstone (with fewer red layers). The Poleslide Member is overlain by the more 

tuffaceous sandstone and mudrocks of the Sharps Formation (fig. 72). 

The Scenic Member consists of a series of ancient soil profiles (paleosols) that developed on a broad,

aggrading floodplain. The white layers represent stream channel bar and over-bank splay flood sand

deposits. The rusty-red layers represent paleosols that developed slowly on broad floodplain surfaces. 

Individual layers of floodplain soil (red) and the sand sheets (white) consist of over-bank, channel bars, and

natural levy deposits. Some beds can be traced for hundreds, even thousands of meters along outcrops. The 

broad extent of individual beds in the Scenic Member suggest that low relief in the region allowed ancient 

stream channels to gradually migrated back and forth across a broad savannah-like floodplain.

The Poleslide Member represents a change to larger stream channels that developed as conditions became 

increasingly drier in the mid to late Oligocene. Continuous streams became more ephemeral, and 

depositional patterns in the rock reflect more episodic flood events than deposition by perennial streams.

Water holes became more important sites for survival of species adapted to open plain environments over 

forests. The Meek and Hayden Survey in the late 1850s originally described the Brule Member as the 

“turtle and oreodon beds.” Remains of land turtles and oreodons (sheep-like animals that dug burrows) are 

51 

 
common in some layers in some areas (fig. 73). Oreodons (a variety named Merycoidodon) and turtles beds 

are part of the lower Scenic Member. Channel sand deposits in the upper Scenic Member were originally

called the “Metamynodon beds” named after bone beds containing an aquatic variety of rhinoceros. The 

Poleslide Member preserves bone beds of a horned sheep-sized herbivore, Proteroceras, and also contains 

oreodons (a variety named Leptauchenia). 

 

The Pig Dig Site 

An example of a fossil discovery happened in the late 1990’s when a park road crew working along Conata 

Road recognized bones in a ditch they were digging (fig. 74). The site has been thoroughly investigated and 

has given the public an opportunity to watch paleontologists conducting the arduous, time-consuming task 

of carefully excavating and preparing fragile fossils for a move to the park’s museum collection. 

52 

 
Sharps Formation 

The Sharps Formation reflects an overall change in geologic and environmental conditions that began 26 to

28 million years ago. The region became even drier, and mammoth ash fall deposits associated with 

tremendous ignimbrite-style volcanic eruptions in the Great Basin region episodically blanketed the 

Badland region. The Sharps consists mostly of tuffaceous sandstones, stream channel sand and floodplain 

mud (paleosols) typical of steppe or even desert-like conditions. Harksen and others (1961) who first

described the formation thought its age was Miocene. The Sharps Formation is now recognized to be latest

Oligocene but is assigned to the Arikaree Group (a group dominated by Miocene-age rocks elsewhere in

the region). 

The highest peaks in the badlands consist of the eroded remnants of Sharp Formation (fig. 75). More 

complete exposures of the Sharps Formation can be seen at Agate Fossil Beds National Park in

northwestern Nebraska (about 200 miles southwest of Badlands National Park). The Sharps Formation 

marks the end of floodplain-style deposition preserved in the park region. If younger Tertiary deposits 

existed in the region they were stripped away by erosion. At the close of the Tertiary Period erosion was 

the dominating force in the region. Down-cutting streams began to exhume the Oligocene strata. On some 

of the highest tableland in the park area are gravel deposits consisting of materials carried by fast-moving 

streams flowing away from the Black Hills. These deposits, called the Medicine Root Gravels, are about 2

million years old and were deposited prior to or near the beginning of the ice ages of the Quaternary period.

Much of the Badlands landscape is a reflection of the erosional history of the region over the past two 

million years.

The Quaternary Landscape 

The modern landscape in the Badlands National Park region is largely a reflection of ongoing erosional

processes over the past several million years. In the late Tertiary the process of regional aggradation 

(building up of sedimentary depositions across a flat landscape) gave way to regional degradation (overall

down cutting of streams into their valleys). The youngest Tertiary-age sedimentary deposit in Badlands

National Park are a thin blanket of Medicine Root gravels cap the highest upland areas in the Pinnacles

Overlook area. These gravels are stream terrace deposits deposited probably in latest Miocene or early 

Pliocene time. These gravels were probably originally derived from fast-flowing streams draining the core

of the Black Hills. These deposits also have a blanket of aeolian dust deposits that gradually accumulated 

during episodic periods of massive dust migration during dryer periods of the Pleistocene. Where

preserved, these surficial dust deposits have since been converted to soil through weathering processes. 

53 

 
Three Rivers Over Time 

The Badlands lies within the headwaters region of three rivers, the Cheyenne, White, and Bad Rivers (figs. 

76 and 77). Through time, these three river systems have gradually carved into the plateau that makes up

the Badlands region (a plateau being an elevated region typically underlain by flat-lying sedimentary

rocks). As a result of stream capture and erosion, mesa and pinnacles of rock are left behind as erosion 

gradually carves back the bounding escarpments or “walls” of this plateau. For instance, the town of Wall 

is named for the east-facing escarpment on the north side of the park that faces the headwater region of the 

Bad River. 

Although the Badlands region was not directly impacted by continental glaciation, the continental glaciers 

are partly responsible for the ongoing landscape development because of their influence on regional river 

systems. Before the ice ages began in the late Tertiary river systems probably drained northward from the 

Western Interior region into the Hudson Bay region. As the larger continental ice sheets formed these north 

flowing rivers were blocked by the advancing glacial ice and large lakes formed along the ice front

(perhaps much larger in area and volume than the modern Great Lakes). Eventually the flooded valleys 

filled to capacity and water flowed over divides into the next lower valley. In this manner the modern river 

systems evolved with the Missouri and Ohio Rivers merging with the Mississippi River system. The 

Missouri River basically follows the southwestern boundary of the last major glaciation.

The original rivers that drained northward into the Hudson Bay region probably had a more gentle stream

gradient than that of the Missouri River when it formed along the southern ice front. As a result, over time 

the Missouri River has carved a gorge about 100m deep for most of its length across the Western Interior

region. This down cutting of the main drainage has been gradually translating upstream into the headwaters 

of all its tributaries, producing the relief we currently see in the Badlands region. The rate of down cutting 

by rivers has not been equal across the region. The Cheyenne River has captured all the major streams 

draining from the Black Hills region, stealing water that probably once flowed into the White River and

other streams. Throughout the western park region are many low divides between the White River and

Cheyenne River valleys. These dry, low divides are an indication that stream capture has occurred. For 

instance, much of the area that is currently drained by Sage Creek probably drained to the south into the

54 

 
White River before stream capture occurred. On the low plateau between South Fork and Dry Creek in the 

southern end of Sage Creek valley are a series of old meandering stream channels left high and abandoned

after stream capture changed the direction of drainage northward into the modern Sage Creek valley.

Stream Terraces: Can They Tell Us About Past Climatic Conditions? 

Bench-like terraces made up of stream gravels are a fairly common occurrence along the sides of stream 

valleys throughout the Western Interior region. For instance, well-developed stream terraces can be seen

along Rapid Creek valley between Scenic and Rapid City. Eliot Blackwelder (1915) recognized these 

terraces (or surfaces) throughout the central Rocky Mountains region and correlated them with major 

glaciation cycles (Blackwelder demonstrated that glacial moraines rest on well-developed terrace deposits 

along major stream drainages and grow progressively older going up section on the valley sides). Many

glaciation periods occurred through the course of the ice ages, but four major glaciation periods are

recognized in the mid-continent region. These major glaciation periods (stages) and interglacial warming 

periods (stades) are interpreted as follows (youngest to oldest; names shown include mid-continent

continental glaciation cycles, International Quaternary stage numbers (IQ), and central Rocky Mountain

glaciation cycles and interglacial “erosion cycles” of Blackwelder, 1915): 

Quaternary and Late Tertiary Time Scale (Stages and Stades) 

Holocene Epoch: (International Quaternary [IQ] stade 1): the current post-glacial warm period (stade) 

beginning roughly 11,000 years ago to the present. The current rise in global sea level following the last

glaciation cycle is called the Flandrian transgression. 

Subdivisions of the Late Pleistocene Epoch: 

Wisconsin glaciation (IQ stages 2 and 4): consists of a series of glacial advances and retreats 

100,000 to 11,000 years ago (called Pinedale glaciation stage in the central Rocky Mountains);

Sangamon interglaciation (IQ stade 5): a mostly warm period between 100,000 to 250,000 years 

ago) (associated with the Lenore erosion cycle in the central Rocky Mountains); 

Illinoian glaciation (IQ stage 6): - consists of a series of glacial advances and retreats 400,000 to

250,000 years ago (called Bull Lake glaciation stage in the central Rocky Mountains); 

Yarmouth interglaciation (IQ stade 7): a mostly warm period between the Illinoian and Kansan

stages (associated with the Circle erosion cycle in the central Rocky Mountains).

Subdivisions of the Early Pleistocene Epoch: 

Kansan Stage (IQ stage 8+) - consisted of a series of glacial advances and retreats 900,000 to

750,000 years ago (associated with the Buffalo glaciation stage in the central Rocky Mountains); 

Aftonian Stade (IQ stade 11+?) - a mostly warm period between the Kansan and Nebraskan 

stages (associated with the Black Rock and(or) Union Pass erosion cycles in the central Rocky 

Mountains); 

Nebraskan Stage (IQ stage 14+?) - consisted of a series of glacial advances and retreats between 

2 million and 1.65 million years ago.

55 

 
Pliocene Epoch and Late Miocene Epochs: 

Early glaciation periods may have occurred in the region prior to 1.65 million years, but no

evidence has clearly established in the Western Interior region. The Fremont surface (also called 

“Summit peneplain”) in the central Rocky Mountains may represent remnants of a late Miocene to

early Pliocene pediment surface. 

The correlation between climatic conditions between glaciation and interglaciations period to surficial 

processes is a complex, unending debate. Because glacial deposits rested on stream terraces in the 

Wyoming region, Blackwelder (1915) correlated the “wetter” glaciation periods with periods of floodplain

broadening. He also interpreted that during the “dryer” interglacial periods streams carved into their 

floodplains. These periods of stream down cutting left remnants of the old floodplains abandoned as stream

terraces along the sides of stream valleys draining uplifts in the Rocky Mountain region. Valley widening 

versus down cutting is related to sediment-transport capacity of streams. And, valley widening occurs when

the valley floor is protected from erosion (during periods of high sediment supply). Down cutting (and

terrace formation) results when the sediment-transport capacity changes so that stream channel erosion 

proceeds faster than the influx of sediment from upstream sources. However, the response of a stream to 

climatic changes may differ over a range of hundreds or thousands of years (Hancock and Anderson, 2002). 

As a result of time averaging, only the major “cycles” will produce long-lasting surficial features that can

be seen today, and the origin of landscape features (such as escarpments or terraces) may be more related to 

past upstream stream-capture events than climatic cycles. 

In the Badlands region terraces are apparent along some stream drainages, perhaps most notably along

Rapid Creek between Scenic and Rapid City. Within Badlands National Park, the broad valley of Sage 

Creek is filled with Late Pleistocene sediments (fig. 78). The modern stream channel of Sage Creek is 

currently incised into this flood plain by about 10 meters. This crosscutting relationship suggests the 

previous valley broadening (flood plain development) occurred during the Wisconsin glaciation cycle, but

specific climate and erosion (and deposition) relationships are unclear. 

Higher “surfaces” in the Badlands suggest earlier cycles of floodplain development followed by stream

down cutting. Throughout the southern Sage Creek Wilderness Area much of the landscape is an

erosionally dissected surface. Areas that hint of older valleys (erosional surfaces) can be seen on an 

enhanced digital elevation model (fig. 79).

56 

 
Eroded surfaces occur in different elevation ranges in different areas. From lowest to highest are:

Sage Creek - The broad valley of Sage Creek in the vicinity of the campground is an elevated floodplain 

about 10 m (30 feet) above current stream level. This surface probably also corresponds to a similar 

elevated floodplain surface throughout the Conata Creek drainage basin region (south of the Badlands

escarpment). Possible association: Pinedale Stage. 

South Fork - A low upland region forms a low dissected plateau that is perhaps best developed in the 

region between South Fork and Middle Fork (of Sage Creek) and their tributaries. This plateau is in the 

range of 30-40 m (100-120 feet) above modern stream level. Possible association: Bull Lake Stage. 

Quinn Table - The broad flat surface of Quinn Table defines a higher erosional surface in the range of 

110-120 m (350 to 400 feet) above stream level. Possible association: Buffalo Stage. 

Pinnacles - The highest surface in the Badlands region is associated with the late Medicine Root Gravels. 

The High Pinnacles in the North Unit and the plateau-shaped Sheep Mountain in the South Unit correlate to

this most ancient surface level. Possible association: Pliocene (Fremont surface)?

Weathering, Mass Wasting, and Erosion 

The evolution of the landscape in Badlands National Park reflects many factors or conditions relating to

bedrock and climate. The contrast in erosion styles between the marine sediments of the Pierre Shale and 

the overlying White River beds demonstrates that the physical and chemical properties of the bedrock are 

important factors in the formation of Badlands topography. The physical processes that change the 

landscape can be subdivided into weathering, mass wasting, and erosion. 

Weathering includes the physical and chemical processes that reduce solid rock at the earth’s surface into 

sediment. It involves mechanical weathering (disintegration of big pieces into small pieces without 

changing the chemical composition of the rock), and chemical weathering (the chemical decomposition of

earth materials, involving a chemical or mineralogical change in composition, and reducing rock into

sediment). 

Mass wasting is the movement of material down an unstable slope as an effect of gravity. Erosion is 

simply the physical removal of sediments to other locations. Erosion of material results in deposition

somewhere else. Surficial sedimentary deposits include alluvium (deposited clay, silt, sand, gravel, or 

similar material from running water), colluvium (sediment deposited at the base of a slope by mass 

wasting), and illuvium (wind-deposited sediments). 

The climate of the Badlands National Park region is an important factor in reviewing weathering and 

erosion processes. Average rainfall is in the range of 17 inches (the range can several inches more in the

higher elevations, and several inches less along the valleys). The driest period is mid winter (December and 

January) when rainfall is typically less than 0.3 inches. About 77percent of the annual precipitation occurs 

57 

 
in late spring and summer (April to September). Average June rainfall is in the range of 3.12 inches (based 

on data from Rapid City International Airport about 40 miles west of the park). This rainfall typically 

occurs in association with short-duration thunderstorms. Winter precipitation occurs with snowstorms that 

are most frequent in March. Average monthly temperatures range from a subfreezing average of 22 degrees

F in January, to an average of 72 degrees in August (with daytime temperatures typically reaching the mid

90s in the afternoon. The park only experiences an average of 130 frost-free days a year. The combination 

of high summer temperatures and short rain events, along with the dry cold winter make growing

conditions difficult for most plants, particularly in the harsh, soil-free conditions in and around the 

badlands. 

Erosion is perhaps most dramatic in the barren landscape of the badlands. Erosion rates are high in the 

barren landscape regions, as much as an inch of sediment per year. 

 

Heavy rainfall from thunderstorms has little ability to soak into the soil-free bedrock, as it flows as a sheet 

wash across the surface into rills (or rivulets) and then into stream channels. Mass wasting (including

slumping and rock falls) contributes sediment directly to stream channels. Heavy rainfall loosens sediment. 

If rain falls faster that the soil or bedrock can absorb it, the water runs off, carrying along sediment. If 

enough rain falls, then flash floods occur. With the abundant clay, silt, and sand derived from the poorly 

consolidated sediments of the White River beds, the flowing water approaches maximum stream capacity 

(the total amount of material [load] which a stream is able to move by the combined processes of solution, 

suspension, and saltation). 

58 

 
Castles, Monuments, Sod Tables, and Hoodoos 

Badlands National Park is best known for its scenic, rugged topography. The term badlands refers to

regions of eroded land on which most of the surface is covered with ridges, gullies, and deep channels, 

having sparse vegetation. 

Landscape features with badlands also have descriptive names, such as follows:

Castles are large star or block shaped barren badlands that are the remaining remnant of bedrock, typically

located at the intersection of multiple stream drainages (see fig. 83). 

A wall is another name for a linear erosional escarpment of badlands. 

A monument is a lone remaining pinnacle of bedrock that rises away from other upland features (such as 

“walls” or “castles”). 

A hoodoo is a typically an inverted cone-shaped erosion remnant of sedimentary bedrock or a hard rock 

(sandstone) resting on a pedestal of softer material (such as clay). Hoodoos are smaller than castles or 

monuments, and are typically numerous in a badlands area. 

Sod Tables are low, typically grass-covered mesas scattered in the valley bottoms between the higher 

castles, walls, and monuments of the badlands (fig. 84). The plateau-like grass-covered surfaces are 

remnants of an earlier floodplain surface (alluvial-colluvial fans) and on White River bedrock. Grasses and 

other plants bind a thin soil that fairly quickly gives way to erosion along expanding headwaters of new

channels. Sod tables occur at several levels ranging from 0.5 to 10 m above channel bottoms in adjacent

59 

 
washes. The sod tables demonstrate that perhaps during a wetter period, perhaps early in the Holocene,

allowed vegetation to become established. Today the region is dryer, and one the thin soil erodes away only

barren badlands remain, and are prone to more intense erosion particularly during infrequent by heavy

precipitation during summer seasonal storms. 

Acknowledgments 

This investigation began with support form a U.S. Geological Survey EDMAP grant in support of

stratigraphic research focused on the Sage Creek Wilderness Area of the North Unit of Badlands National

Park. This research, partially supported by a U.S. Geological Survey EDMAP grant, is a follow-up to

investigations to dissertation research (Stoffer, 1998 and Terry, 1998.) This research is a cooperative effort 

involving the authorities of the National Park Service, the U.S. Geological Survey, the South Dakota 

Geological Survey, and CUNY, Brooklyn College, Department of Geology.

Selected Internet Links 

Badlands National Park website: http://www.nps.gov/badl/. 

Badlands National Park, USGS-NPS Vegetation Mapping Program Products: This website includes aerial

photography and information on climate, soils, Wildlife and vegetation:

http://biology.usgs.gov/npsveg/badl/. 

Ecoregions of North Dakota and South Dakota, 43. Northwestern Great Plains:

http://www.npwrc.usgs.gov/resource/1998/ndsdeco/43h.htm. 

Stoffer, P., P. Messina, J. A. Chamberlain, Jr., D.O. Terry, Jr. 2001, The Cretaceous-Tertiary Boundary 

Interval in Badlands National Park, South Dakota: U.S. Geological Survey Open-File Report 01-056,

online at: http://geopubs.wr.usgs.gov/open-file/of01-056/. 

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