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
East Coulee, Alberta a land area of , it had a population density of in 2011. East Coulee, Alberta East Coulee is a community within the Town of Drumheller, Alberta, Canada. It was previously a hamlet within the former Municipal District (MD) of Badlands No. 7 prior to the MD's amalgamation with the former City of Drumheller on January 1, 1998. It is also recognized as a designated place by Statistics Canada. East Coulee is located on Highway 10, approximately southeast of Drumheller's main townsite and northeast of Calgary. It lies in the Red Deer River valley and has an elevation of .