The Missouri Escarpment is what remains of west and southwest wall of a giant ice-walled and bedrock-floored canyon

The Missouri Escarpment is a 100-200 meter high northeast-facing erosional escarpment extending in a southeast direction from Alberta across Saskatchewan to the North Dakota northwest corner and then into central North Dakota. In central North Dakota the Missouri Escarpment becomes an east-facing escarpment and extends south to south central South Dakota. The Missouri Escarpment was formed when giant supra-glacial melt water rivers carved an immense southeast- and south-oriented ice-walled and bedrock-floored canyon into a decaying North American ice sheet. The ice-walled and bedrock-floored canyon detached the ice sheet's southwest margin. The Missouri Coteau, located between the Missouri Escarpment and the present day Missouri River valley represents where the ice sheet's detached margin was located.