The curvy road between Ellensburg and Yakima looked so much more interesting on the map than the interstate. It was! State Route 821 follows the Yakima River through a canyon for much of that distance.
The otherworldly landscape is the result of a gigantic lava flow some 6-17 million years ago. Lava flooded tens of thousands of square miles in what is now Washington, Oregon and Idaho. As the basaltic lava flowed out of the Earth's crust the crust below collapsed, forming the hilly Columbia Plateau. The area east of the Cascades is pretty much a desert -Yakima only gets eight inches of rain a year- so there's not enough water to support trees except along the river.