The Blaine Site - South Dakota State Historical Society

Chapter 2
ENVIRONMENTAL
CONTEXT
2.1 The Black Hills Environment
2.1.1 Physical Geology
The Blaine site is located in the southwestern Black Hills in western Custer
County, South Dakota. The Black Hills are the easternmost extension of the
Rocky Mountains. The Black Hills have been described structurally as an elongate
dome or doubly plunging anticline, rising 3000–4000 feet above the surrounding
high plains (DeWitt et al. 1986:9; Rich 1981). The Black Hills attain
their highest elevation at Harney Peak, 7242 feet above sea level. The average
elevation of the Black Hills region is about 4000 feet. The elliptical Black Hills
uplift extends approximately 120 miles north to south and 50 miles east to west.
It covers an area of about 6000 square miles (15,500 square km) (Froiland 1978;
Rich 1981). About two-thirds of the Black Hills lie in western South Dakota,
with the remaining area extending into northeastern Wyoming. The Black Hills
are structurally similar to other Rocky Mountain outliers (Prucha et al. 1965;
Dandavati 1981:21).
The Black Hills takes its name from the Lakota Paha Sapa, Black Mountains.
The name refers to the dark color imparted the hills by a dense cover of
ponderosa pine. Several other unique physical features break the grassy high
plains surrounding the Black Hills. These include the White River Badlands to
the southeast, Bear Butte on the northeastern periphery, and the Bighorn and
Laramie mountains to the west.
The Black Hills uplift encompasses five physiographic zones (Darton and
Paige 1925). The four main geological formations form concentric rings around
an upthrust central core. The physiology follows the same pattern due to differential
resistance of the various exposed rock strata (Figure 2.1). The four
main physiographic zones are, from the center outward, the Central Basin or
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