Geology:
The history of the canyon's formation begins about 26 million years ago to the Oligocene period, when most of Oregon was covered by ocean. After the waters of the ocean receded about 15 million years ago, the flood basalt flows of the Columbia River Basalt Group covered the sandstone that had been the ocean floor. The softer layers of sandstone beneath the basalt sheet eroded over time, creating pathways behind some of the waterfalls that Civilian Conservation Corps workers widened to make safe for public use. Another geologic feature are many tree "chimneys" or casts, formed when hot lava engulfed living trees and disintegrated them.
