258 TERENCE T. QUIRKE 
Creek, drain the mountains to the south and southeast (Bigs72): 
From a distance the mountains appear to slope toward the north 
and northwest in long, smooth plains. Closer inspection, however, 
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MONTANA 
SOUTH DAKOTA iSiaaltie 
2 10 20 30 40 Miles 
Fic. 2.—Map showing the distribution of the White River formation (shaded) 
in North Dakota. Abandoned Pleistocene channels are indicated by dashes. (After 
Leonard.) 
shows that these slopes are fragmentary, and that many are decapi- 
tated by the tributaries of the Little Missouri River. These 
creeks have extended their heads westward through the gap between 
the mesas, so that in some places parts of two drainage systems 
