During the last ice age, Badger Mountain experience some of the largest freshwater floods known to have happened anywhere on Earth. This is an incredible part of the geological history that shaped our area. FOBM Volunteer David Comstock is passionate about sharing this story with the visitors that hike the Canyon Trail.
The light gray granitic rocks you see from the Canyon Trail, are not native and were ice-rafted here from the Sandpoint, Idaho area during Ice Age Floods. In Geology, “erratics” are rocks that differ from the surrounding native bedrock and were moved here from their place of origin. The light gray erratics you see from the Canyon Trail originated in British Columbia, Canada (over 300 miles away) and were carried into the Purcell Trench to the Sandpoint area of northern Idaho with the advance of glacial ice during the last ice age. Then these rocks were ice-rafted here during Ice Age Floods after the cataclysmic failure of the ice dam at least 15,000 years ago.
The Lake Lewis slackwater deposits, along with other evidence indicates that Badger Mountain may have experienced as many as ninety (90) Ice Age Floods during the last glacial period. To understand the number of Ice Age Floods, geologists look to rhymically layered sediments deposited in slackwater (slow water) areas of Lake Lewis. Each layer (called a rhythmite) grades upward from sand at the bottom (the sand is first to settle out the floodwater) to silt at the top. Each individual rhythmite layer was deposited by a separate Ice Age Flood.
In the 1920s, a geologist named Harlen Bretz spent years studying the massive landforms of eastern Washington, collectively known as the “Channeled Scablands”. Bretz noted that streams in many of the canyons were far too small to have eroded such deep valleys such as Grand Coulee. The presence of features like “dry falls”, massive granite boulders on top of basalt cliffs, huge gravel bars and other glues led Bretz to conclude that these geological features were created by some sort of massive flood. But the mystery for Bretz was where did the flood water come from?