The Wild Horse Basin Wilderness Study Area (WSA) (OR-3-77B) is located east of Owyhee Reservoir in Malheur County, Oregon, approximately 26 miles south of Vale and 36 miles northwest of Jordan Valley. U.S. Highway 20 lies 20 miles northwest of the WSA and U.S. Highway 95 is 15 miles east of the area.
The WSA contains 12,100 acres of BLM lands and 580 acres of split-estate lands. In addition, a 40-acre parcel of private land is located in the southeast portion of the WSA, accessed by an existing way. The study area is crescent shaped, approximately 6.5 miles long east to west, and three miles wide north to south at its center. The boundary of the WSA consists of roads on the south and east and Bureau of Reclamation-administered land on the north and west. A dead-end road enters the WSA from the south near Indian Creek, forming part of the boundary and extends 3.5 miles to a developed spring in Wild Horse Basin. All boundary roads are considered to be high standard dirt roads. The acreage and boundary description vary from that in the Final Oregon Wilderness Environmental Impact Statement (EIS) due to the inclusion of 580 acres of split-estate lands acquired in a land exchange with the State of Oregon.
The terrain varies from steep and rugged slopes fronting the Owyhee Reservoir to rimmed plateaus and rolling hills in the eastern portion of the WSA. The canyons and ridges contain numerous basalt outcrops and rims. Elevation ranges from 2,600 feet along the west boundary near Owyhee Reservoir to 4,700 feet along Owyhee Ridge near the east boundary. Vegetation in the WSA consists mainly of sagebrush, native bunchgrasses, and cheatgrass.
The WSA was initially identified and studied under section 603 of the Federal Land Policy and Management Act (FLPMA) with additional acquired estate lands studied under section 202. The WSA was included in the Final Oregon Wilderness Environmental Impact Statement filed in February 1990.