Located in central Washington, on the opposite side of the Upper Grand Coulee from the Columbia River, is a 3.5-mile long and 400-foot high scalloped precipice known as Dry Falls. As the name suggests, Dry Falls no longer carries water, but at one time, it was once the largest waterfall that is known to have existed on earth. It is five times the width of the Niagara falls and more than twice its height. It is speculated that during the last ice age, catastrophic flooding channeled water at 65 miles per hour through the Upper Grand Coulee and over this 400-foot rock face. At this time, it is estimated that the flow of the falls was ten times the current flow of all the rivers in the world combined.
Nearly twenty thousand years ago, as glaciers moved south through North America, an ice sheet dammed the Clark Fork River near Sandpoint, Idaho. Consequently, a significant portion of western Montana flooded, forming the gigantic Lake Missoula. Water covering three thousand square miles of northwest Montana, about the volume of Lake Ontario, was locked behind this glacial dam. Eventually, rising water in lake Missoula broke through the ice dam creating a cataclysmic flood that spilled into Glacial Lake Columbia, and then down the Grand Coulee. The massive torrent (known as the Missoula Flood) ran wild through the Idaho panhandle, the Spokane River Valley, much of eastern Washington and into Oregon, flooding the area that is now the city of Portland under 400 feet of water. The tremendous force of the Dry falls eroded away so much earth and rock, that the precipice fell back by 15 miles to its present position.
Once the ice sheet that obstructed the Columbia melted, the river returned to its normal course, leaving the Grand Coulee and the falls dry. Today, this massive cliff can be viewed from the Dry Falls Interpretive Center, part of Sun Lakes State Park, and located on Route 17 near the town of Coulee City.
It is generally accepted that this process of ice-damming of the Clark Fork, refilling of Lake Missoula and subsequent cataclysmic flooding happened dozens of times over the years of the last Ice Age.
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