Bounded by the Cascade Mountains to the west and the Blue Mountains to the north, Oregon’s high desert covers approximately 24,000 square miles. Annual rainfall in the high desert varies from 5 to 14 inches. The average elevation is 4,000 feet; at 9,733 feet, the summit of Steens Mountain is the highest point in Oregon’s high desert. The terrain of the high desert was mostly formed by a series of lava flows that occurred between 30 and 10 million years ago.