THE GEOLOGY OF THE KILLDEER MOUNTAINS, 
NORTH DAKOTA 
TERENCE T. QUIRKE 
University of Minnesota 
The physiography of the Killdeer Mountains illustrates a case 
of rejuvenation without uplift. The drainage was rejuvenated 
by the deflection of the Little Missouri River due to the approach 
of an ice sheet.’ The deflection, which brought the Little Missouri 
River much nearer the mountains than it was before, produced a 
great increase in the gradient of the mountain streams. 
A study of the rocks extends the known distribution of Oligocene 
formations in the Northwest. Much of the rock is limestone, and 
the formations appear to have been made by wind, river, and 
lake actions. 
LOCATION AND DESCRIPTION 
The Killdeer Mountains are in the western part of North 
Dakota, about halfway between Manitoba and South Dakota, 
and 50 miles east of the Montana line. They are part of the water- 
shed between the Missouri and Little Missouri rivers, the watershed 
extending 250 miles southward to the Black Hills. The mountains 
consist of two mesas, called North Mountain and South Mountain, 
which are surrounded by cliffs which in some places are more than 
too feet high. The mountains cover an area of about ro square 
miles, but they are so deeply cut into by streams that the plateau 
tops are less than 23 square miles in area, and the periphery of the 
plateaus is about 30 miles. Most of the mountain area consists 
of slopes covered with talus and landslides, deep, wide valleys, 
and foothills characterized by decapitated slopes. Here and there 
steep-sided peaks rise from the plateaus, the highest being about 
3,200 feet above sea-level, and about 150 feet above the plateaus. 
The mesa tops, which are upheld by a series of interstratified sand- 
stone and limestone layers, are about 500 feet higher than the plains. 
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