RECONSTRUCTING A CATASTROPHIC FLOOD FROM PLEISTOCENE LAKE ALVORD AND LAKE COYOTE INTO THE OWYHEE RIVER BASIN, SOUTHEASTERN OREGON

A catastrophic flood from Pleistocene Lake Alvord and Coyote Lake traveled eastward into the Owyhee River as a result of Lake Alvord rising and spilling into Coyote Lake during a pluvial cycle. Previous work by Lindberg and Hemphill-Haley (1988) and Reheis (1999) indicates that Lake Alvord rapidly incised a channel up to 15 meters deep at least once through a low point in the Tule Springs Rim into Coyote Lake, releasing approximately 1.8x 1010 m3 of water. This spillover caused Coyote Lake to rise rapidly and catastrophically overflow the northern and eastern rims, with a combined spillway width of 7 kilometers. The resulting flood traveled northeasterly down the Crooked Creek drainage and into the Owyhee River. Flood features include high-water marks up to 50 meters above the current channel, deeply incised canyons, plucked bedrock surfaces, imbricated boulder bars containing boulders up to 2 meters in diameter, tear-drop shaped hills and boulder bars perched on drainage divides. A strongly developed shoreline at the level of the incised outlet in Coyote Lake suggests that sustained overflow probably connected the Owyhee River (Columbia River drainage) to the northernmost Great Basin for an extended period after the flood. This hydrologic connection may have facilitated migration of aquatic species from the Columbia River drainage into the Great Basin of southeastern Oregon.