Nature & Science

The gently rolling high plains of western South Dakota give way to the dramatic vistas of Badlands National Park within sight of Minuteman Missile National Historic Site

NPS

 

The Minuteman changed the northern plains, but the missile system was one small moment in the region's far broader natural history. Western South Dakota is a land rich in geological and natural features.

Landscape Surrounding Minuteman Missile National Historic Site

Launch Control Facility Delta-01 and Launch Facility (Missile Silo) Delta-09 are on the American Great Plains, which farmers and ranchers have historically used to graze cattle and cultivate crops. Intermingled with the farm and ranch lands is the Buffalo Gap National Grassland, which is managed by the United States Forest Service. As a result, the open landscape surrounding the missile sites is broken only by changes in topography and a few low-profile buildings. Tall vegetation is sparse.

Geology of Western South Dakota

The Western Plains of South Dakota are part of the Great Plains and are the least populous section of the state. Landforms in the Great Plains are unglaciated and retain soils formed by shallow seas that covered the region approximately seventy-five million years ago. The other major geologic region, in the area is known as the Black Hills. These were formed by pressure from the earth's tectonic plates that forced subsurface rock upward to create a sixty-mile-wide and 125-mile-long region known for its natural beauty.

The seas that once covered South Dakota's Western Plains deposited limestone and sandstone overlain by soft Pierre shale. As the shale eroded through water and wind action, the rolling terrain in the Western Plains emerged, leaving short-grass plains mixed with eroded river valleys. The Badlands lie within the Great Plains. The striking landscape of the Badlands emerged from the process of erosion caused by water and wind, which created tall spires of sedimentary rock and exposed rich fossil deposits.

Topography

Delta-01 and Delta-09 are within the northern Great Plains physiographic province, which is characterized by rolling mixed-grass prairie. Elevations range from about 2,550 feet to 2,700 feet.

Climate & Weather

Southwestern South Dakota's climate is semiarid, characterized by hot summers and cold winters. In January, the average minimum temperature is about 7° Fahrenheit; the average high is about 33°. In July, the average maximum temperature is 90°. On average, 13 summer days exceed 100°. Winds of 50 miles per hour can occur, most likely in the summer. Average annual precipitation is 16 inches, falling predominantly in May, June, and July. Thunderstorms are common, and are the main source of spring rainfall. Heavy rains can cause flash flooding along minor tributaries. Yearly snowfall averages 35 inches, and a few heavy snowstorms occur each year. Snow combined with heavy winds can create snowdrifts of several feet, making road maintenance and travel difficult.

Water Resources

An intermittent steam course runs south of Interstate 90, near Launch Control Facility Delta-01. This area also contains a few small pockets of wetlands. There are no known water resources at or near Launch Facility (Missile Silo) Delta-09.

Soils

The soil along Interstate 90 near Delta-01 and Delta-09 is of the Camborthids- Argiustolls subgroup, which has a clayey texture. The soil shrinks when dry and swells when wet. In dry weather, this type of soil can develop cracks up to two inches wide, 40 inches deep, and several feet long. Load-bearing strength is low. These two qualities of shrink-swell potential and low strength can cause construction limitations. Permeability is very slow to moderate, while runoff is moderate to rapid. Moderate erosion due to either water or wind is a risk. The bedrock type is shale, which may be 30 to 60 inches below the surface.

Vegetation

The Interstate 90 corridor from Wall to the turnoff for Badlands National Park at Cactus Flat is within the mixed-grass prairie of the Great Plains. The United States Forest Service has conserved the area surrounding the study area as the Buffalo Gap National Grassland. The area is characterized by medium-height grasses, with few areas of shrubs and trees. The dominant grass species are western wheatgrass and green needlegrass. Localized areas can be dominated by short grasses of blue gramma and buffalograss during times ofstress. Forbs commonly associated with the mixed grasses include scarlet globe mallow, American vetch, prickly pear, and fringed sagewort. Years of higher precipitation can encourage little bluestem bunchgrass.

Shrubs and trees are usually restricted to draws, gullies,and surface waters. Typical shrub species include silver buffaloberry, broomsnakemeed, greasewood, and some plum and chokecherry. Cottonwoods, willows, ash, and elms are common tree species growing along streams.

Wildlife

The grasslands along the Interstate 90 study corridor provide habitat for a variety of wildlife species. Large game animals include the pronghorn, mule deer, white-tailed deer, coyote, and bobcat. Among the smaller mammals present are red fox, striped skunk, badger, jackrabbit, prairie dog, and a number of species of other rodents and ground squirrels.

Amphibian and reptile species may include the Great Plains toad, painted turtle, garter snake, and western rattlesnake. United States Forest Service sensitive species (that is, species tending towards being a candidate for Federal listing as threatened) which are possibly found along Interstate 90 are tiger salamander, northern leopard frog, pale milk snake, northern earless lizard and northern prairie lizard.

Birds in the area include upland game birds such as pheasant, grouse and turkey. In addition, there are several raptor and hawk species including turkey vultures, eagles, red-tailed hawks, kestrels, ferruginous hawks, Swainson's hawks, prairie falcons, and occasionally peregrine falcons.

Wetland and riparian habitat along the Interstate 90 corridor support shorebirds, waterfowl, and other birds. Species that may be found in some of these habitats include redwing blackbirds, yellow-headed blackbirds, common yellowthroats, snipes, spotted sandpipers, and American avocet. Long-billed curlews may be present. Species that may be seen near marshes include short-eared owls and the northern harrier. Wetlands support a wide variety of migratory waterfowl. Species that may visit these wetlands include coots, Canada geese, herons, whooping cranes, pelicans, and numerous species of ducks.