LATE TERTIARY HISTORY OF UPPER MISSOURI RIVER 53 



mouth of Milk River, about 20 miles below Glasgow. Another 

 old valley, noted by the writer in 191 1, extends from Poplar, Mon- 

 tana, northeastward to Medicine Lake, thence eastward for several 

 miles, thence northward to the vicinity of Dagmar and Coalridge, 

 and thence northeastward to the lake region of the extreme north- 

 western corner of North Dakota. Beyond this the old river cha^^- 

 nel is completely buried by drift. 



.^T El^-^H^t — &--^E]s-r 



Fig. I. — Map of Upper Missouri River, showing some Tertiary river channels. 

 By C. M. Bauer. 



In the vicinity of Poplar this old valley is nearly filled with 

 glacial drift. The town of Poplar is built on a moraine, as shown 

 by the section of drift 45 feet thick just north of the Indian School 

 on Poplar River. Northeast of Poplar for several miles the drift 

 is probably much thicker. In T. 28 N., R. 52 E., and northeast- 

 ward for 20 miles the trough of the old valley is from 3 to 4 miles 

 wide, with broad, gentle slopes on either side. Near Medicine 

 Lake it widens, and on its south bank there is an area of sand dunes. 



