Horse Ridge is a long system of volcanic ridges in eastern Deschutes County, Oregon, south of Highway 20 near Millican and the Oregon Badlands Wilderness. Shaped by volcanic and tectonic forces rather than forming a single peak, it is cut by the Brothers Fault Zone, and exposed mafic lava here dates to about 7.5 million years ago. Part of the area has been protected since 1967 as the Horse Ridge Research Natural Area, mainly on north- and northeast-facing slopes. With open volcanic terrain, a high desert setting, and about 30 miles of trails, Horse Ridge has both scientific value and year-round recreational appeal.