Geology and Physiography of the Crow Reservation
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.
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.
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.