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
Birch Coulee Battlefield edge is a steep wooded ravine, a landform known locally by the French term "coulee," also spelled "coulie" or "cooley." Birch Coulee, known to the Dakota as "Tanpa Yukan" (Place of the White Birch), is deep and runs for a total of down to the Minnesota River. A few hundred yards to the west of the coulee, the prairie rises slightly onto a gentle knoll. On September 1, 1862, a burial detail of about 170 Union Army volunteers and civilians under Major Joseph R. Brown camped on the prairie west of Birch Coulee. The site was selected by Captain Hiram