Sediments underlying northwestern South Dakota include rocks assignable to the Pierre (shale), Fox Hills (sand), and Hell Creek formations of Cretaceous age and the Ludlow and Tongue River formations of the Paleocene. These rocks may be exposed at the surface, but usually are overlain by relatively thin soils that are mostly derived from them; the best soil in the county for agricultural purposes is the loessal sandy or silty loam in the northeastern quarter, which is derived from Tongue River sediments (Baker, 1952). [Illustration: FIG. 1. Map of Harding County, South Dakota, showing location of places named in text.] The climate of northwestern South Dakota is characteristic of the northern part of the interior grasslands of North America--that is, the winters are cold and the summers hot and dry. Weather data for the period 1896-1967 at Camp Crook are representative of those gathered at the several stations maintained in the county. At Camp Crook the mean temperature for January is 17.3 F, whereas that for July is 71.2 F; precipitation averages 13.17 inches annually, most falling in the months of April through September; snowfall amounts to an average of 33.2 inches per year and is recorded from every month from September through May (Climatogeography of the United States, no. 20-39, Camp Crook, South Dakota, 1969). Major surface drainage systems in Harding County include the Little Missouri River, which flows northward through most of the western part of the county, the South Fork of the Grand River, which originates in the east-central part of the county and flows generally eastward, and by the North Fork of the Moreau River, which originates in the south and drains in a southeasterly direction. Permanent standing surface water was virtually unknown prior to the development of artificial impoundments. [Illustration: FIG. 2. Central part of Slim Buttes as viewed from the east.] Vegetation of the grassland areas in the county is typical of that found throughout the semi-arid Northern Great Plains. Cover on upland soils, especially those that are clayey in substance, generally is sparse; areas along water courses and well-watered sites elsewhere tend to have denser stands of grasses such as bluestem (_Andropogon_). Dominant grasses of upland are gramma, buffalo grass, wheat grass, stipa, and tickle grass. Sage (_Artemisia_) and numerous forbs are prominent in many areas. These grasslands are used extensively for grazing of sheep and cattle. [Illustration: FIG. 3. Fuller Canyon, North Cave Hills.] [Illustration: FIG. 4. Little Missouri River southwest of Ladner. Note beaver dam in background and nature of riparian community.] [Illustration: FIG. 5. Stand of pines on northern part of Slim Buttes.] [Illustration: FIG. 6. Draw with deciduous trees in North Cave Hills.] [Illustration: FIG. 7. Spring-fed artificial impoundment in Deer Draw, Slim Buttes.] [Illustration: FIG. 8. Farm land in northeastern part of Harding County.]