 Soap Lake is formed at the end of a chain of lakes running down the center of the Lower Grand Coulee.The Lower Grand Coulee is over a mile and a half wide in places with sheer basalt rock walls rising 900 feet over the coulee floor.State Highway 17, Coulee Corridor-National Scenic Byway, runs through Soap Lake and up the floor of the canyon heading towards Grand Coulee Dam and Canada.