The high desert is named as such for its generally high elevation, averaging about across the region. It is bordered by the eastern foothills of the Cascade Range to the west. The Blue Mountains are the geographical boundary to the north, marking the northern end of the high desert's semi-arid plateau. The southern high desert is part of North America's Basin and Range Province, which extends south through Nevada and Arizona and into Mexico. It contains large alkali lakes and tall cliffs, some with a prominence of more than . Steens Mountain, in Harney County, is the highest point within the region; its summit is above sea level. To the east, the high desert country of the Columbia Plateau extends across the Snake River and into Idaho.