Palouse Falls State Park Heritage Site
Palouse Falls is a geologic wonder in east central Washington. The rock here is part of the Columbia River Basalt Group, which covers over 81,000 square miles of the earth's surface in eastern Oregon, eastern Washington, western Idaho, and part of northern Nevada. Most of the basalt erupted between 14 and 17 million years ago, or the middle-late Miocene epoch. We do not need to delve deeper into the volcanic history of the region, but consider that you see these remarkable basalt outcrops in many parts of the state east of the Cascades.
The spectacular canyon and the waterfall at the state park are a result of immense floods that burst from Glacial Lake Missoula. Near the end of the last continental glacial era, about 15,000 years ago, a lobe of ice blocked the drainage of what is now the Clark Fork River. The water that backed up created Glacial Lake Missoula, a major body of water that may have included as much volume as the combined present Lakes Erie and Ontario. As the water level rose, pressure against the ice dam increased and caused the ice to float. The dam failed and a mass of water rushed westwards (see the figure below). Peak flow may have been as high as 386 million cubic feet per second (cfs). As a comparison, the flow of the Mississippi River at Old River Control during the record 2011 flood was 2 million cfs.
Floodwaters rushed across east central Washington towards the Columbia River valley and on to the Pacific. The waters carved an immense network of channels, canyons, and valleys, creating what we now call the Channeled Scablands. These included Grand Coulee, where the dam is now located, Dry Falls, and Palouse Falls. Flood waters even reached south deep into the Willamette Valley of Oregon, where they deposited masses of sediment. Geologists now estimated that there were at least 40 of these pulses of water that occurred over a period of about 2,500 years.
Consider the time scale. The earth is about 4.5 to 5 billion years old. The Missoula Floods occurred about 15,000 years ago, only a is a tiny fraction of earth's history. Humans may have come to North America during the last glacial maximum between 21,000 and 23,000 years ago (based on footprints found at White sands National Park). Therefore, predecessors of our present native Americans saw these floods.
The Washington Department of Natural Resources has an excellent interactive presentation of Washington's Ice Age floods.
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| Areas affected by floods (teal color), from the Montana Natural History Center, Glacial Lake Missoula Chapter. Note the ice lobe that extended south into the Puget Lowlands. |
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| Palouse Falls from the visitor's center (Samsung phone digital file) |
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| View southwest (downstream) of the Palouse River. The terraces outline successive basalt flows. (50mm ƒ/2 Rikenon lens) |
Washtucna
Washtucna is a small town in Adams County about 17 miles north of Palouse Falls and about a hour from Spokane, Walla-Walla, and Pullman. The town is at the head of the Washtucna Coulee (again, one of the remnants of the Missoula Floods) and is therefore lower than some of the surrounding terrain.
The town looked like it had gone through a rough time economically. I saw some interesting subject material along Main Street (Route 261).
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| El Camino (28mm ƒ/2.8 Vivitar lens) |
References
Waltham, T., 2010. Lake Missoula and the Scablands, Washington, USA. Geology Today, pp 152-159DOI: 10.1111/j.1365-2451.2010.00763.x
