Geological History

1. About 20 million years ago this region was humid and the topography was a network of streams and hills. There was no Cascade Range, and moisture-laden clouds sweeping inland from the Pacific created an environment in which a rich and diversified forest thrived. 2. Floods of molten basaltic lava welled up through fissures in the earth’s crust, eventually engulfing an area of 200,000 square miles to a general thickness of several thousand feet. Between eruptions lakes and marshes formed and forests grew. With each lava flow the forests were destroyed. Some logs were engulfed, preserved, and ultimately petrified. 3. With the end of the outpouring of lava about 6 million years ago the raising of the Cascade Range began. This uplift cut off the moist winds from the west, leaving Eastern Washington an arid region. Erosion by the elements, rivers and floods cut through one lava flow after another exposing the petrified wood as we see it today