The wooded buttes mentioned above are at least in part within the boundaries of Custer National Forest and support western yellow pine (_Pinus ponderosa_) and junipers (_Juniperus_ sp.). In some ravines and other protected sites there are groves of deciduous trees such as cottonwood, aspen, boxelder, ash, hackberry, elm, dogwood, and hawthorn, usually associated with shrubs such as buckbrush, chokeberry, plum, currant, and gooseberry. These groves frequently are associated with small springs, as the one in Deer Draw of the Slim Buttes. The major water courses and their tributaries are essentially treeless, although occasional stands of cottonwoods and other deciduous trees and shrubs occur in some places--for example along the Little Missouri near Camp Crook. Some representative habitats in Harding County are illustrated in Figs. 2-8. Our interest in Harding County dates from August of 1960, when one of us (Jones) and Robert R. Patterson visited the area briefly and obtained a small collection of mammals. Subsequently, field parties from the Museum of Natural History collected mammals in the county in the periods 14-30 June 1961, 23 March-11 April 1963, 5-7 July 1965, and 13 May-11 June 1968. Incidental collection also occurred in the extreme western part of the county in the period 29 June-24 July 1970 when a group was working primarily in the Long Pine Hills of adjacent Carter County, Montana. There are few published references to mammals in Harding County. Visher (1914), in an early biological survey of the area, listed 40 species of mammals, but his accounts are mainly of historic value. Subsequently, publications by Bailey (1915), Young (1944), Goldman (1944), Over and Churchill (1945), Jones and Genoways (1967), and Henderson _et al._ (1969) have recorded mammals from the county. ACCOUNTS OF SPECIES Fifty-three species of mammals known from Harding County, South Dakota, are treated in the accounts that follow. Appended is a brief discussion of 10 additional species that may be found there. In most accounts, specimens that have been examined (a total of 644) are listed in telegraphic style preceding remarks; localities are arranged from north to south in such lists. Unless otherwise noted, specimens are housed in the Museum of Natural History. All measurements are in millimeters (those of embryos are crown-rump lengths) and weights are given in grams. Order Chiroptera ~Myotis evotis evotis~ (H. Allen, 1864) Long-eared Myotis _Specimens examined_ (20).--NW 1/4 sec. 15, R. 5 E, T. 22 N, 2; 5 mi. N, 2 mi. W Camp Crook, 1; 10 mi. S, 5 mi. W Reva, 16; 7 mi. S, 4-1/2 mi. E Harding, 1.