Basalt rock comprises the foundation for much of Idaho, eastern Washington & eastern Oregon. This bedrock is volcanic, or igneous, rock resulting from the cooling of basaltic lava exposed at or near ground surface. From approximately 17 to 7 million years ago a series of massive lava flows oozed over wide stretches of these lands. In some places the flows were a thousand or more feet thick. Evidence of such deep deposits can be seen while descending Graves Creek as it makes its way to the Salmon River. Along the way massive basalt columns and cliffs are stunningly exposed.