 As the Okanogan lobe grew the Columbia was rerouted into the Grand Coulee.Flowing across the current Grand Coulee-Dry Falls region, the ice-age Columbia then entered the Quincy Basin near Quincy, Washington & joined Crab Creek at Moses Lake, following Crab Creek's course southward past the Frenchman Hills and turning west to run along the north face of the Saddle Mountains, there to rejoin the previous and modern course of the Columbia River just above the main water gap in the Saddle Mountains, Sentinel Gap.During this period the Missoula Floods periodically discharged large volumes of water, some of which reached Upper Crab Creek by overtopping the divide between the Columbia drainage and the Crab Creek drainage, and some diverted into the Columbia River to enter Crab Creek at Moses Lake.