The Pembina Escarpment, a rise of 300 to 400 feet along the western edge of the valley, defines the beginning of the central surface-step, the Drift Prairie, or Drift Plain. At the northern end of the escarpment, which is a continuation of the Manitoba Escarpment in Canada, lie the wooded Pembina Mountains, jutting sharply above the valley floor. South of these hills the rise is less pronounced except at the southern end, where the hills again become prominent to merge with the Coteau des Prairies, an escarpment lying chiefly in South Dakota. Glacial deposits, or drift, of finely ground rock, sand, and gravel give the Drift Prairie its name. It is a rolling, fertile plain, varying from 70 to 200 miles in width, and broken by low ridges of hills, shallow coulees, and numerous small lakes. To the northwest lies the Souris River Valley, a small glacial lake bed resembling the Red River Valley. Devils Lake, largest in the State, lies in the northern part of the Drift Prairie, and together with Stump Lake forms the basis of the interior drainage system; near its southern end are the headwaters of the James and Sheyenne Rivers, both flowing southward, the James into the Missouri and the Sheyenne into the Red. The Missouri Escarpment, rising 300 to 400 feet above the Drift Prairie and cutting across the State diagonally in a northwest-southeast direction, marks the rise of the third surface-step, the Missouri Plateau, which extends west to the Rocky Mountains. Lying along the top of the plateau, in some places not far from the escarpment and at other points 50 miles west of it, is the Altamont Moraine, a belt of rough, stony hills, indicating the farthest advance of the Dakota lobe of the Wisconsin ice sheet. In the north this moraine is a part of the Height of Land forming the watershed between the north-and south-flowing streams of the continent. Between the escarpment and the Missouri River the plateau is known as the Couteau du Missouri. West of the river it is known locally as the Missouri Slope. The surface of the plateau, typical of the Great Plains, is irregular and rolling, dotted with old lake beds--some of which contain large deposits of sodium sulphate--and underlain with vast lignite beds and valuable clay and bentonite deposits. In the Missouri Slope is the most unusual area in the State--the Badlands of the Little Missouri. Here erosion has formed, and continues to form, a fantastic array of buttes in which layers of brick-red scoria and gray, blue, and yellow clays are vividly exposed. Abrupt buttes and mesas characterize the landscape, increasing in size and number toward the southwest corner of the State. Among them is Black Butte, 3,468 feet above sea level, the highest point in North Dakota. CLIMATE