Welcome to the Frenchman's Basalt Columnars! Whats a basalt columnar? Glad you asked. Here is a quick geology lesson
During late Miocene and early Pliocene epochs, one of the largest flood basalts ever to appear on the Earth's surface engulfed about 63,200 sq mi of the Pacific Northwest, forming a large igneous province with an estimated volume of 41,800 cu mi. Eruptions were most vigorous from 14–17 million years ago, when over 99 percent of the basalt was released. Less extensive eruptions continued from 14–6 million years ago. When the lava flows finally cooled, vertical and horizontal fractures formed in each layer of the basalt. This huge area of basalt is known as "The Columbia River Basalt Group" which covers portions of Washington, Idaho and Oregon.
Then the glacial floods came! About 15,000 to 17,0000 years ago, glacial Lake Missoula was formed when the Cordilleran Ice Sheet damned the Clark Fork River near the Idaho-Montana border causing the valleys of Western Montana fill with water up to 2000 feet deep in places forming the massive Lake Missoula. Lake Missoula was the size of Lake Erie and Lake Ontario COMBINED! When the lake filled enough to float the ice dam, the ice dam eventually broke cause a catastrophic flood to hit eastern and central Washington. This massive torrent of water literally carved-out the fractured basalt and forming the Frenchman Coulee and the columns you see before you. The cycle of the ice sheet blocking the flow of the Clark Fork River, causing Glacial Lake Missoula to form and the ice dam breaking and then flooding of the scablands of Central and Eastern Washington numerous times during that period of time. The repeated glacial flooding caused erosion that both exposed and and/or undermined the basalt formations you see today.
Now you know how these awesome basalt formations came to be, now its time for some observations and answers to some questions to get credit for this earthcache. Please email me directly your answers to the following questions. DO NOT post your answers in your "found it" log:
1) Counting from the pointy formation of basalt on your left (the formation that looks like an arrow pointing up), continue to the right to the end of the row of columns of basalt, how many individual basalt columns do you see?
2) State your estimated height range of this row of columnar basalt.
Any "found it" logs without emails with the answers to the questions will be deleted. No armchair finds, please. The point is to get you out to this beautiful location to see the wonders of the Columbia River Gorge area. Please note that the coordinates are located within Washington Department of Fish and Wildlife lands and thus requires that you have either have a Discovery Pass to park at the listed coordinates OR you purchase a day pass at the nearby kiosk. Another option is you can park along the road and walk in.
Special thanks to Tom Foster and hugefloods.com for inspiration and the use of the maps/diagrams used on this page and to Central Washington University Professor Nick Zentner for his awesome "2 Minute Geology" videos! You ROCK Professor Zentner!