TEE GEOLOGY OF NORTH DAKOTA 2i 



About 25 miles north and east of the Killdeer Mountains, in 

 eastern McKenzie County, many of the high buttes are capped with 

 200 feet of strata resembhng those in the Killdeer Mountains. It is 

 believed that the greenish sandstones and greenish clays of these 

 buttes are likewise to be referred to the White River formation. 



The strata in all these locahties are clearly only remnants of 

 much larger areas which have suffered extensive erosion and only 

 relatively small patches of the White River formation have been 

 left. It is not unlikely that several of those nearest together may 

 formerly have been connected. 



The beds of this formation are in part lake deposits and in part 

 river deposits. Those of Sentinel Butte, the easternmost areas in 

 Grant County, and most of the beds of the Killdeer Mountains are 

 doubtless of lacustrine origin, while portions of the deposits of White 

 Butte and the next area to the north are likewise lake deposits. 

 The coarse pebbly sandstones and perhaps other strata were 

 deposited by rivers. 



While western North Dakota was an area of deposition in 

 Lowest Eocene or Paleocene time and also during the early part 

 of the Oligocene epoch, nevertheless during most of the Tertiary 

 period the region was undergoing erosion. This resulted in the 

 removal of many hundreds of feet of strata over most of the state, 

 and in places the aggregate thickness of the Cretaceous and Ter- 

 tiary deposits thus carried away by streams amounted to 1,000 

 feet and over. The outlier known as the Turtle Mountains, the 

 Fort Union strata of which were once continuous with those of the 

 Missouri Plateau, was during this time separated from the plateau 

 by the denudation of the intervening area. The broad depression 

 of the Red River Valley was cut to a depth of 800 to 900 feet in the 

 Cretaceous and older rocks of eastern North Dakota and Minne- 

 sota by a large northward-flowing river. The topographic features 

 of the region west of the Missouri River, including the rolhng up- 

 lands, the high ridges and divides, the numerous buttes, the escarp- 

 ments, and badlands, were all formed in large measure by erosion 

 during the Tertiary period, continued, of course, in the Pleistocene. 

 Since the Cretaceous and Tertiary strata were deposited they 

 have undergone but little deformation, though the region has 

 several times been elevated, in the aggregate to the extent of some 



