This section provides descriptions of the most prominent and distinctive geologic features and processes in Theodore Roosevelt National Park.

Figure 13. View of Badlands from Oxbow Overlook. Theodore Roosevelt National Park is an ideal setting for the development of badlands topography. Badlands formation with its high-drainage density is probably the most distinctive geologic process in the park. NPS photo by Dave Krueger.

Myriad natural features contribute to the development of badlands topography at Theodore Roosevelt National Park (figure 13). Among these factors are intense seasonal storms; relatively soft, easily erodible rocks; and the absence of dense stabilizing vegetation. Badlands formation is probably the most distinctive geologic process occurring in the park. Badlands topography is discussed in detail in the "Geologic Setting," "Coal Resources and Mining," and "Geologic History" sections. Other features and processes of the landscape at Theodore Roosevelt National Park are presented in alphabetical order here.

Concretions and Cap Rocks
Concretions are hard, compact aggregates of mineral material. They precipitate out of solution from groundwater. Prior to the regional erosion of the Little Missouri badlands, groundwater slowly seeped through the layers of sediments for millions of years. This water contained minerals, which precipitated then cemented around sand grains or other nucleus (e.g., shell or bone fragments). Some concretions are remarkably large, especially in the North Unit. For example, along the scenic drive near Squaw Creek Campground, large, round concretions called "cannonballs" have eroded out of the surrounding rock and accumulated at the base of the cliffs (Murphy et al. 1999). Erosion- resistant concretions preferentially weather out of the basal sandstone of the Sentinel Butte Formation. Many of these concretions form the resistant caprock of pedestals (also known as rain pillars or hoodoos). These cap rocks are flat, hard, sandstone slabs that protect the underlying sediments from erosion. Eventually the slabs will tilt or fall off the pedestals and the remaining soft sediments will quickly erode away (Murphy et al. 1999).

Glacial Erratics
Large boulders once transported by glaciers now rest scattered on bedrock surfaces different from their own compositions, a position which testifies to the effectiveness of glacial erosion and transport. Many erratics have glacial striations or scratches that formed as they were dragged against bedrock during glacial movement. Glacial erratics of granitic and carbonate compositions are the primary evidence of glaciation in Theodore Roosevelt National Park (Biek and Gonzalez 2001). They occur in the North Unit and are thought to mark the maximum extent of glacial ice in this part of the Missouri Plateau. Most of the erratics are 1 to 2 feet (0.3 to 0.6 m) in diameter, but some are almost 5 feet (1.5 m) in diameter (Biek and Gonzalez 2001).

Eolian Deposits
Windblown deposits such as loess and sand cover large areas of the Great Plains. This wide eolian distribution throughout the region was recognized almost as soon as geological exploration began in the late 19th century (Emmons et al. 1896; Gilbert, 1896). Though sporadically mapped and underrepresented on most geologic maps, investigators of Quaternary climate change have renewed scientific interest in loess and eolian sand (Madole 1995). Lengthy loess sequences, such as those present on the northern Great Plains, contain detailed records of Quaternary glacial- interglacial cycles. Scientists consider these to be a terrestrial equivalent to the foraminiferal oxygen isotope record of deep- sea sediments, which document long- term climate change (Muhs et al. 1999). Loess is also a direct record of atmospheric circulation. Information on paleowind from loess in the geologic record can test atmospheric general circulation models (Muhs et al. 1999). In addition, widespread eolian deposits are important sources of information for reconstructing the history of aridification in the interior of North America during the Quaternary (Madole 1995).

In North Dakota, sediments deposited during the Pleistocene Epoch (1.8 million years ago to 11,800 years ago) belong to what geologists call the Coleharbor Group. Sediments deposited during the Holocene Epoch (11,800 years ago to present) belong to the Oahe Formation. Loess is present in both of these units. Although most upland surfaces are veneered with loess, and dune sands are locally present, neither were mapped by Biek and Gonzalez (2001). Loess is difficult to map where it is thin (less than 5 feet [1.5 m]) or overlies rocks that weather to residuum that is texturally similar to loess, as is the case in much of the badlands region (Madole 1995).

Figure 14. Oxbow Overlook. The Little Missouri River makes a huge bend as it turns east in the North Unit. Eventually, the river will
abandon the large U-shaped portion of the channel and flow in a more direct course, leaving an oxbow. NPS Photo by Dave Krueger.

Oxbows
The erosion and deposition of sediments associated with active streams constantly change riparian ecosystems. In the valleys at Theodore Roosevelt National Park, streams tend to meander-widening their bends and occasionally short- circuiting them. This leaves the abandoned meanders as oxbow lakes, which slowly fill in with sediment (figure 14). Remnants of these filled lakes record this process as ongoing along the Little Missouri River (Laird 1956). Today, the Little Missouri River makes a wide bend as it turns east in the North Unit. Eventually, the river will abandon the large U- shaped portion of the channel in favor of a more direct route, leaving a stranded oxbow (Murphy et al. 1999).

Pediments
Pediments are broad, erosional, low- angle bedrock surfaces, extending out from highland margins. They are correlative with arid and semiarid conditions and are associated with landscape development over time. However, the connection between pediments and climate is still a subject of debate among geomorphologists (Summerfield 1991).

In Theodore Roosevelt National Park pediments occur at the bases of major escarpments and the heads of major drainages. In the South Unit, the largest pediment surfaces are located at the foot of the eastern escarpment, in the vicinity of Boicourt and Sheep Butte springs, and at the heads of Sheep, Paddock, and Jones creeks. In the North Unit, large pediments occur along Squaw Creek and the Little Missouri River (Biek and Gonzalez 2001). Pediments in the park are complex assemblages in which erosional surfaces have been buried by sheetwash sediment or reworked eolian material (see "Sheetwash Erosion" and "Eolian Deposits" sections). These conditions make interpretation and study of landscape development via pediments difficult in the park.

Sand and Gravel
Sand and gravel are present in alluvial deposits (units QTa and Qt on the geologic map) in the North and South units of Theodore Roosevelt National Park. These deposits occur as a veneer capping high- level plateaus near the Little Missouri River. A thick mantle of Holocene loess often covers these deposits.

Sand and gravel have been mined by private entities from at least two places inside park boundaries. The first location, at the eastern edge of the Petrified Forest Plateau, probably provided sand and gravel for road material (used locally) and the trail leading to the top of Petrified Forest Plateau (Biek and Gonzalez 2001). In 2002 the National Park Service acquired the second location-a 5,510- acre (2,230 ha) land acquisition containing 960 acres (389 ha) of sand and gravel potential. This property was previously owned by Ken and Norma Eberts who periodically sold gravel from the site to Billings County for road improvements. The National Park Service extinguished sand and gravel rights in conjunction with the buyout of the parcel of land (Phil Cloues, NPS Geologic Resources Division, written communication, October 18, 2004).

Figure 15. Shelter at Riverbend Overlook. The Civilian Conservation Corps used medium-grained, cross-bedded sandstone from a
local quarry to construct various structures in the park, such as this shelter in the North Unit. NPS photo by Dave Krueger.

Sometime before 1957, sand and gravel deposits were also mined from another location atop the plateau immediately east of Medora. This currently unreclaimed pit is located just outside the park's boundary. A large landslide is present on the steep slope just west of the pit (Biek and Gonzalez 2001). Sandstone and Silcrete During the 1930s, the Civilian Conservation Corps used medium- grained, cross- bedded sandstone from a quarry near Theodore Roosevelt National Park to construct various structures in the park. For example, rough blocks of what is likely Sentinel Butte sandstone surround the perimeter of the shelter at the Riverbend Overlook in the North Unit (figure 15). Large blocks of the same sandstone and silcrete blocks of the Taylor bed (upper unit of the Bear Den Member of the Golden Valley Formation) line the path down to the shelter. Silcrete is silica- cemented sand and gravel. Investigators are uncertain whether these stones were quarried in the park. A 1937 photo caption implies that the quarry was in the North Unit, but a longtime park employee was certain that the quarry was located 25 miles (40 km) southwest of the park in an area called Flat Top Butte (Biek and Gonzalez 2001). At present, investigators have not seen any evidence of sandstone quarrying within Theodore Roosevelt National Park (Biek and Gonzalez 2001).

In 1938, the Emergency Relief Association built the old South Unit entrance station. This check station, adjacent stone fence, and privy are made from cut and dressed sandstone blocks of unknown origin. A pylon constructed of this same stone upon which the park's name hangs was originally at the check station. It was moved to the Painted Canyon Visitor Center in 1968 (Biek and Gonzalez 2001).

Sheetwash Erosion
In densely vegetated environments, the presence of stabilizing plant roots usually prevents rills from developing. By contrast, in arid and semiarid environments such as Theodore Roosevelt National Park, where precipitation tends to fall in intense bursts, erosional features such as rills and gullies naturally develop. The slopes of many of the buttes in the park are extremely gullied or minutely dissected by running water. Rill- and- gully erosion occurs particularly in the basal sandstone of the Sentinel Butte Formation.

The movement of water across a slope surface is called sheetwash. This is a general term because, unlike a sheet, water flow is never of uniform depth due to microtopography of hillslope surfaces. Sheetwash typically grades into channelized flow as the water movement becomes progressively more concentrated into particular downslope routes. For this reason, the distinction between "sheet flow" and "channelized flow" is sometimes indefinite. Nevertheless, sheetwash flowing from the sides of a butte in the badlands will typically concentrate into tiny rills as a result of irregularities of the slope. Some of these rills break down between rainfall events; others enlarge into gullies that deepen and widen with each rain. As rills develop into gullies, they erode back into the butte until two rivulets meet at their heads. The divide between them becomes very narrow and more succeptible to rapid weathering and erosion. Eventually, the divide between the two rivulets degrades entirely, separating a small portion of the butte side from the main butte. Thus, the butte erodes incrementally by both the action of running water and by this process of segmentation (Laird 1956).

Terraces
Changes in channel gradient, discharge, or sediment load can cause a river to incise its floodplain and form terraces. River terraces also can be cut into previously deposited alluvium or bedrock. Following incision, the original floodplain is abandoned and left as a relatively flat bench (terrace), which is separated from the new floodplain below. River terraces are inclined downstream but not always at the same angle as the active floodplain. The valley wall of an entrenching river may contain a vertical sequence of terraces. The lowest, youngest terrace may retain traces of floodplain morphology, whereas the highest, oldest terrace may be heavily weathered. Terraces can be either paired or unpaired. Paired terraces on opposite sides of the river form when vertical incision occurs more rapidly than the lateral migration of the channel. Unpaired terraces form when rapid lateral shifting of the channel occurs and the river cuts terraces alternately on each side of the valley floor.

In general, geomorphologists differentiate terraces and assign ages based on height above the modern stream level. For example, in the South Unit, alluvial terrace deposits (unit Qt on the geologic map) are subdivided into four mappable units (from youngest to oldest): Qt1, Qt2, Qt3, and Qt4.

Terraces in Theodore Roosevelt National Park record changes caused by a major climatic cooling event during the Pleistocene Epoch. This cooling caused the advance of large continental ice sheets from northern latitudes. In pre- glacial time, the Little Missouri River flowed north toward Hudson Bay. However, when glaciers advanced southward, local north- flowing streams were blocked; the drainages of the Little Missouri and Yellowstone rivers were diverted along the edge of the ice front. This ice- marginal drainage eventually became the present Missouri River, which the Little Missouri River flows into. The rate of erosion and downcutting of the Little Missouri River was not constant: as erosion and deposition continued, the river cut a series of terraces, remnants of which can be seen in the park (Harris and Tuttle 1990).

References:

Biek, R. F., and M. A. Gonzalez. 2001. The geology of Theodore Roosevelt National Park, Billings and McKenzie counties, North Dakota. Miscellaneous Series 86, text (74 p.), 2 pls. (scale 1:24,000). Bismarck: North Dakota Geological Survey.

Harris, A. G., and E. Tuttle. 1990. Geology of national parks, 4th ed. Dubuque, IA: Kendall/Hunt Publishing Company.

Laird, W. M. 1956. Geology of the North Unit, Theodore Roosevelt National Memorial Park. Bulletin 32. Bismarck: North Dakota Geological Survey.

Madole, R. F. 1995. Spatial and temporal patterns of late Quaternary eolian deposition, eastern Colorado, U.S.A. Quaternary Science Reviews 14:155-177.

Muhs, D. R., J. B. Swinehart, D. B. Loope, J. N. Aleinikoff, and J. Been. 1999. 200,000 years of climate change recorded in eolian sediments of the High Plains of eastern Colorado and western Nebraska. In Colorado and adjacent areas, Field Guide 1, eds. D. R. Lageson, A. P. Lester, and B. D. Trudgill, 71-91. Boulder, CO: Geological Society of America.

Murphy, E. C., J. P. Bluemle, and B. M. Kaye. 1999. Roadlog guide for the South & North units, Theodore Roosevelt National Park. Educational Series 22. 2nd printing. Bismarck and Medora, ND: North Dakota Geological Survey North Dakota Geological Survey, and Theodore Roosevelt Nature and History Association.

Summerfield, M. A. 1991. Global geomorphology: An introduction to the study of landforms. New York: John Wiley & Sons, Inc.