Just west of Coulee City, Washington, highway US-2 crosses a dike holding back a sizable reservoir, Banks Lake, in a wide canyon, the Grand Coulee. (In Washington, “coulee” is a localism for a flat-bottomed canyon with steep sides). Banks Lake resembles several storage reservoirs in the arid lands of the American West. It even has the usual recreational infrastructure such as marinas, boat-launch ramps, and bait shops. However, it is unusual, indeed unique, in a fundamental way: Grand Coulee is an abandoned Ice Age channel that carries no modern river….
