Grand Coulee at the higher side of the flexure. Encountering the steep slope of the monocline, the new river would have cascaded off the rim, down onto a broad plain where Coulee City and Dry Falls State Park now stand. Upper Grand Coulee began as an cascade just north of Coulee City. As the rush of water eroded the surface, it steepened into a waterfall. The falls continued to erode backward (northward) creating the canyon. When the falls reached the divide into Lake Columbia, i.e., preglacial Columbia Valley, it disappeared, leaving the elongated notch. Today, the waters of the Lake Roosevelt are
Coulee City, Washington Coulee City, Washington Coulee City is a town in Grant County, Washington. The population was 562 at the 2010 census. The town was named after nearby Grand Coulee. Coulee City was officially incorporated on May 10, 1907. Coulee City is located at (47.611942, -119.290904). According to the United States Census Bureau, the town has a total area of , all of it land. As of the census of 2010, there were 562 people, 265 households, and 150 families residing in the town. The population density was . There were 331 housing units at an average density of . The racial