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
Etzikom Coulee of at its origin east of Stirling Lake (to which it is connected by the Sluice Gate Channel) to an elevation of at its mouth at Pakowki Lake, over a length of more than . The coulee builds a canyon up to deep. Etzikom Coulee Etzikom Coulee is a coulee located in Southern Alberta, Canada. The waterway was formed as a glacial spillway channel at the end of the last ice age. The Etzikom Coulee begins northeast of the town of Stirling, and makes its way southeast of the Hamlet of Wrentham, after that it passes by the Hamlet of