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Scientists and writers have described the resulting Bonneville Flood in various ways. They say it discharged an estimated 15 million cubic feet per second through nearby Marsh Valley, raging on to the and increasing its flow by about 500 times. Water and debris — including limestone blocks the size of houses — scoured to bedrock the river’s igneous channel, en route to the Northwest’s and the Pacific Ocean. The volume is said to have been six times the flood flow of the Mississippi River, and three times the average flow of South America’s Amazon River. The flood’s crest at the Portneuf Narrows, near modern Pocatello, may have reached 410 feet high. Most of the resulting downstream carving and erosion occurred in a matter of days or weeks, but the discharge probably continued for more than a year, investigators say.

The release was the catastrophic beginning of the end for Lake Bonneville. The highest lake level, visible as a terrace on surrounding mountain slopes for hundreds of miles around, is called the Bonneville Shoreline. The end of the most recent Ice Age, and accompanying climate change — warmer and drier conditions — further depleted Lake Bonneville as it evaporated, leaving other long-term “bathtub ring” terraces, including the Provo, Stansbury and Gilbert shorelines. All that was left is today’s comparatively shallow , and other “puddles,” such as Lake and usually dry Sevier Lake. And the draining left plenty of room for today’s lake-bottom cities and towns, including Salt Lake City, Provo, Ogden and dozens of other communities in Utah, in southern and even in eastern Nevada.