Steens Mountain, Fault-block mountain in Harney County, United States.

Steens Mountain is a single fault-block mountain in Harney County, Oregon, not a range, stretching about 50 miles north to south. Its east face rises roughly 5,500 feet from the Alvord Desert to a 9,738-foot summit, built of stacked basalt flows. The bare gray-brown and purple surface shows diagonal ridges and shallow gullies above a flat, cracked desert floor.

The mountain was named in 1860 after an Army officer stationed in the region during frontier operations. The area later became a protected zone to balance outdoor recreation with traditional land use practices.

The Steens Mountain Cooperative Management and Protection Area, created by the Steens Mountain Cooperative Management and Protective Act of 2000, covers 425,000 acres. The law bars mining on 1,200,000 acres and cattle grazing on 100,000 acres. The name honors Major Enoch Steen, who in 1860 drove Paiute people off the mountain.

The main access road is open from late spring through early fall, with several pullouts for viewing canyons and distant vistas. Bring layers of clothing since weather changes quickly at higher elevation and temperatures can be surprisingly cool.

The east face exposes more than forty stacked basalt flows, some reaching 3,000 feet thick. In one layer, the magnetization of its quickly cooled top and bottom points opposite to that of its interior, which cooled over about ten days; geologists explained this in 2003 by the rock's magnetic properties rather than a rapid field reversal.