Geology of the Pacific Northwest along their course. The larger cataract was that of the upper Grand Coulee, where the river roared over an waterfall. The eroding power of the water plucked pieces of basalt from the precipice, causing the falls to retreat and self-destruct by cutting through to the Columbia River valley near what is now the Grand Coulee Dam. The other major cataract is now known as Dry Falls. It started near Soap Lake in Washington State, where less resistant basalt layers gave way before the great erosive power of this tremendous torrent and waterfalls developed. As in the upper Grand Coulee, the
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