Moses Coulee Coulee, a National Natural Landmark, one of the largest examples of bars created by the Channeled Scablands outburst floods. Moses Coulee cuts into the Waterville Plateau, which lies in the northwest corner of the Columbia River Plateau. The plateau is part of the Columbia River Basalt Group, a large igneous province that lies across parts of the states of Washington, Oregon, and Idaho in the United States of America. During late Miocene and early Pliocene times, one of the largest flood basalts ever to appear on the earth's surface engulfed about 163,700 km² (63,000 mile²) of the Pacific Northwest, forming
Grand Coulee Dam the year. For example, while the dam may generate at nameplate-capacity in the spring, decreased river flow in the fall means less power can be generated the rest of the year, resulting in a lower capacity factor. The proposal to build the dam was the focus of a bitter debate during the 1920s between two groups. One group wanted to irrigate the ancient Grand Coulee with a gravity canal while the other pursued a high dam and pumping scheme. The dam supporters won in 1933, but for fiscal reasons the initial design was for a "low dam" tall which would