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Geology and Physiography of the Crow Reservation

This page was written by Erin Klauk as part of the DLESE Community Services Project: Integrating Research in Education. Funding was provided in part by the Montana Office of Public Instruction .

Map of Montana labeling Crow Reservation. Details

The largest reservation in Montana, the Crow Reservation, is located on the Great Plains physiographic province. It is mostly in Big Horn County in south central Montana and is bordered by Wyoming to the south. The reservation is approximately 60 miles wide and 40 miles in length, encompassing 1,574,394 acres. This area ranges from mountains to plains. The high lands consist of the Wolf Mountains to the east and the Big Horn and Pryor Mountains to the south. Sloping down to the north from the mountains are rolling upland plains, which make up most of the reservation, and vary in altitude from 3,000 to 4,500 feet. The alluvial low lands are located along the Big Horn River, Little Big Horn River, and Pryor Creek drainage systems.

Stratigraphic column for Bighorn Canyon National Recreation Area, Montana and Wyoming.
Stratigraphic column for Bighorn Canyon National Recreation Area, Montana and Wyoming. Details

The geologic setting of the Crow Reservation includes the west flank of the Powder River basin, a northwest-trending synclinal feature at least 250 miles long and as much as 100 miles wide in eastern Wyoming and southeastern Montana; the south flank of the Bull Creek syncline, a large east-trending fold in central Montana; and the northern parts of the Bighorn and Pryor uplifts which extend from south-central Montana southeast into Wyoming. These features, and many subsidiary folds and faults associated with them, were formed in early Tertiary (Eocene) time (Richards, 1955, p. 77-78 ) and account for the distribution of rock units in the reservation, the oldest rocks being exposed in the core of the Bighorn uplift where it has been breached by deep canyons tributary to the Bighorn River, and the youngest rocks, exclusive of surficial stream terrace deposits and alluvium, being exposed east of the Little Bighorn River on the flank of the Powder River basin (Status of Mineral Resource Information for the Crow Indian Reservation, Montana (more info) ).

There is about 11,000 feet of sedimentary rock exposed in the Crow Indian Reservation, including rocks from Precambrian to Tertiary time. These rocks are resting on Precambrian metamorphic and igneous rocks that can been seen in the Bighorn Mountains (Status of Mineral Resource Information for the Crow Indian Reservation, Montana (more info) ). For a detailed description of the structural geology of this area, including folds and faults, refer to The Status of Mineral Resource Information for the Crow Indian Reservation, Montana Report (more info) .


To further investigate the geology of the Crow Reservation, follow the links below.

Geology of the Crow Reservation

Resources containing information about the geology of the Crow Reservation.

  • A Preliminary Assessment of Paleontological Resources at Bighorn Canyon National Recreation Area, Montana and Wyoming. This report provides information about the stratigraphy and paleontological resources that occur throughout the Paleozoic and Mesozoic formations exposed in the Bighorn Canyon National Recreation Area, including information on a wide diversity of fossil forms. (more info)
  • Crow Indian Tribe: Geology and Minerals Resources Report. This 8-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section thoroughly describes the geology and minerals of the Crow Reservation. Topics covered are stratigraphy, structure, oil and gas, coal, and paleontological resources. Also included is a general geologic section illustrating the bedrock units found on the reservation. (more info)
  • Crow Indian Tribe: Soils Resources Report. This 4-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section thoroughly describes the soils found on the Crow Reservation. (more info)
  • Soils Appendix. This 14-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section features a soils appendix for the Crow Reservation. Included are tables illustrating the areal extent of soil map units and soil series characteristics for the Powder River and Billings area, as well as soils maps for this area. (more info)
  • Status of Mineral Resource Information for the Crow Indian Reservation, Montana. This US Department of Energy report provides information about the status of mineral resource information for the Crow Indian Reservation in south-central Montana. Information is included about the geology and mineral resources of the area. Maps, graphs and tables are included to aid in illustrating this information. (more info)
  • Geology of the Bighorn Canyon--Hardin Area, Montana and Wyoming. [Richards, 1955] This USGS Bulletin provides a descriptive analysis of the geology of the Bighorn Canyon in the Hardin area of Montana and Wyoming. (citation and description)

Geologic Maps of the Crow Reservation

Resources containing geologic map information for the Crow Reservation.



To further investigate the physiography of the Crow Reservation, follow the links below.

Physiography of the Crow Reservation

Resources containing information about the physiography of the Crow Reservation.

  • Crow Indian Tribe: Land Use and Realty Resources Report. This 9-page PDF is part of the final statewide oil and gas environmental impact statement and proposed amendment of the Powder River and Billings Resource Management Plans. This section thoroughly describes the land use and realty of the Crow Reservation. Also included are maps illustrating surface and mineral ownership, land use and vegetation, grazing districts, and development opportunities. (more info)
  • Geologic Provinces of the United States: Interior Plain Province. This USGS site provides an overview of the geologic history of the interior plains province. External links lead to information about national parks that exhibit interior plains geology and similar overviews of other physiographic provinces. An image gallery and additional maps and illustrations are also provided. (more info)
  • The Geologic Story of the Great Plains. This site provides a non-technical description of the origin and evolution of the landscape of the Great Plains physiographic province. Information about the history and descriptions of the various landforms of the Great Plains is included. (more info)



For ideas on how to use these webpages in a classroom, a Study Guide is provided.




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