Columbia River Basalt Group map shows main regions of basalt exposure in Washington, Oregon, Idaho and Nevada, USA. (usgs.gov)- Steens Mountain (Wikipedia)
Steens Mountain is a large fault-block mountain in the northwest United States, located in Harney County, Oregon. Stretching some fifty miles (80 km) north to south, on its west side it rises from the Alvord Desert at an elevation of about 4,200 feet (1,280 m) to 9,738 feet (2,968 m) at the summit. Steens Mountain is not part of a mountain range but is properly a single mountain, the largest of Oregon’s fault-block mountains.