Black Hills, 3,700 mi2 (9,600 km2)
Land-surface form.--The Black Hills are a maturely dissected domal uplift with an exposed core of Precambrian rocks; encircling hogbacks, enclosed hogbacks, and enclosed strike valleys rim the province. The Black Hills are actually a low mountain with a relief of 1,000-5,000 ft (300-1500 m). The plains surrounding the Black Hills have altitudes of 3,000-3,500 ft (900-1,100 m), compared to an altitude of 7,242 ft (2,207 m) for Harney Peak, the highest peak in the Black Hills. Most of the peaks in the central area of the Black Hills have altitudes between 5,000 and 6,600 ft (1,520 and 2,010 m).
Climate.--The climate is temperate steppe. Winters are cold, with temperatures below freezing. The average annual temperature ranges from 48F (9C) at lower elevations to 37F (3C) at higher ones. The frost-free season varies from 80 to 140 days, depending on altitude. Annual precipitation, which ranges from 15 to 26 in (380 to 660 mm), falls mostly as winter snow, despite a spring maximum.
Vegetation.--Because there is more precipitation than in the surrounding semiarid plains, the Black Hills support an evergreen forest made up of eastern, western, and northern forest species. Because elevations barely exceed 7,000 ft (2,100 m), there are no significant alpine or subalpine zones. White spruce, extending southward from Canada, is the only dominant on higher slopes in the montane zone; there is no Douglas-fir. Paper birch from the northern conifer forest is also present. Aspen covers considerable areas, presumably indicating fires in the past. Ponderosa pine dominates most lower slopes in the montane zone, with lodgepole pine from the Rockies found in small numbers. Along streams and rivers, eastern broadleaf species are common, including ash, hackberry, elm, birch, and bur oak.
Intervening valleys form open parks. Shrubs such as sagebrush are common. At the lower edge of the montane zone, ponderosa pine grows in scattered open stands and savannas. Encroaching on the grasslands, it is periodically burned back.
Soils.--Most of the soils are Alfisols.
Fauna.--Large mammals such as elk, mule deer, and whitetail deer are common. Small herds of bison and pronghorn antelope populate the grasslands, along with colonies of blacktail prairie dogs. Red squirrels abound, and Harney Peak is inhabited by mountain goats recently introduced into the region.
Many bird species occur throughout the Black Hills, some typically western, some more eastern in range, including the blue jay, dark-eyed junco, and gray jay.
Amphibians include the Great Plains toad.