Long before the Ice Age floods could carve the coulees, waterfalls, and cliffs that dominate this landscape, basalt was needed, and in huge quantities! Vents from deep in the earth's crust supplied the basalt, erupting again and again to cover much of eastern Washington and parts of Oregon and Idaho in a layer cake of basalt thousands of fee thick. Over time, tectonic forces pushed and pulled at the bedrock, opening deep fractures in the basalt.
Millions of years later, Ice Age floods swept through this area. The floodwaters took advantage of these fractures, cutting steep chanels where the bedrock was weakest and creating Palouse Falls and its canyon. The floods also changed the course of the river.
(Left Illustration Caption)
During the height of the floods, this entire area was under hundreds of feet of water. This painting shows a flood in progress after the water level dropped several hundred feet.
(Center Illustration Caption)
Palouse Falls today.
(Right Photo Caption)
See the large crack in the basalt cliffs across the canyon? This is one of the fractures in the basalt opened by tectonic forces coming from deep within the earth. Can you see any others?