Arguably the most famous stretch of the Columbia River is that portion which slices through the heart of the Cascade Mountains, a mountainous and heavily forested region known simply as, "The Gorge". Further upriver, however, in eastern Washington and Oregon, the Columbia dissects its way through a less well-known landscape that is as dramatic and dry as the Cascades are wet. Here, the land spreads out in the rain shadow of the mountains where annual rainfall may top out at 10 inches per year or less, and the forests are replaced by sagebrush, rabbitbrush, and grasslands.
Exposed in the cliffs high above the river are an amazing assemblage of volcanic rocks which appear to ascend from river level to the canyon's rim like a gigantic staircase. These rocks tell a tale of vast floods of lava that covered much of what is now the northwestern United States only 17 to 14 million years ago. During that geologic time interval, known as the Miocene, fissures opened in the earth's crust in present day eastern Oregon and eastern Washington out of which thousands of cubic kilometers of molten rock poured. Some of the individual lava flows were so large, they managed to make it all the way to the Pacific Ocean, over 300 miles to the west. Long after these lava flows cooled to become the black volcanic rock basalt, the Columbia River began cutting its channel through this layer cake to reveal to us one of the important chapters in the fascinating geologic history of this region.
