range from . The Clarno Unit, the westernmost of the three units, consists of located west of Fossil along Oregon Route 218. The Painted Hills Unit, which lies about halfway between the other two, covers . It is situated about northwest of Mitchell along Burnt Ranch Road, which intersects U.S. Route 26 west of Mitchell. These two units are entirely within Wheeler County. The remaining of the park, the Sheep Rock Unit, are located along Oregon Route 19 and the John Day River upstream of the unincorporated community of Kimberly. This unit is mostly in Grant County; a small part extends into Wheeler County. The Sheep Rock Unit is further subdivided into the Mascall Formation Overlook, Picture Gorge, the James Cant Ranch Historic District, Cathedral Rock, Blue Basin, and the Foree Area. Some of these are separated from one another by farms, ranches, and other parcels of land that are not part of the park. The park headquarters and main visitor center, both in the Sheep Rock Unit, are northeast of Bend and southeast of Portland by highway. The shortest highway distances from unit to unit within the park are Sheep Rock to Painted Hills, ; Painted Hills to Clarno, , and Clarno to Sheep Rock, . The John Day River, a tributary of the Columbia River, flows generally west from the Strawberry Mountains before reaching the national monument. It turns sharply north between the Mascall Formation Overlook and Kimberly, where the North Fork John Day River joins the main stem. Downstream of Kimberly, the river flows generally west to downstream of the unincorporated community of Twickenham, and generally north thereafter. Rock Creek enters the river at the north end of Picture Gorge. Bridge Creek passes through Mitchell, then north along the eastern edge of the Painted Hills Unit to meet the John Day downstream of Twickenham. Intermittent streams in the Clarno Unit empty into Pine Creek, which flows just beyond the south edge of the unit and enters the John Day upstream of the unincorporated community of Clarno. History Early inhabitants of north-central Oregon included Sahaptin-speaking people of the Umatilla, Wasco, and Warm Springs tribes as well as the Northern Paiutes, speakers of a Uto-Aztecan (Shoshonean) language. All were hunter-gatherers competing for resources such as elk, huckleberries, and salmon. Researchers have identified 36 sites of related archeological interest, including rock shelters and cairns, in or adjacent to the John