Grand Coulee Columbia Rivers pathway and onto the southern plateau creating an ice dam. This dam backed up the waters of the Columbia into Glacial Lake Columbia and later during the Missoula Floods forced those waters into eastern Washington, creating the Scablands. The river at Grand Coulee found no existing valley and thus forged its own pathway across the divide, creating the Upper Coulee. The plateau is not level, but is marked with wrinkles and upfolds of the basalt. The diverted waters of the Columbia, encountered the monoclinal flexure, a steep warping up of toward the northwest. Lake Columbia topped the ridge
Battle of Birch Coulee side of the Minnesota River with a force of 350 Indians. Gray Bird's party and Brown's troops missed encountering each other during the day, but some Indian scouts discovered that Brown's troops were moving toward the campsite at Birch Coulee. The Sioux planned to ambush Brown's troops in the morning, thinking that only the cavalry was present and that they could be easily destroyed. The Birch Coulee campsite was not easily defensible, since the Indians could approach from all sides and still remain under cover. Also, since the burial detail felt themselves safe, they did not take precautions against attack