94 PROCEEDINGS OF THE AXX ARBOR MEETING 



Illinoian gumbotil, wliicli is at least five feet tliick, outcrops near the valley 

 walls of the Iowa-Cedar River and along both sides of the Mississippi. Hence 

 these two valleys are incised below the Illinoian upland plain and are post- 

 lUinoian gumbotil in age. Therefore the lake could not have found its dis- 

 charge by way of them, and the displaced Mississippi must have followed the 

 course south of Columbus Junction until the lake was eventually drained by 

 way of the Iowa-Cedar River valley. The thickness of the deposits in the lake 

 basin, the well wave-rounded shorelines, and the relation of the contact be- 

 tween the lake and the fluvial terrace all point to the same conclusion regard- 

 ing the long duration of Lake Calvin. 



Due to stream piracy of the streams developed on the newly formed Illinoian 

 drift plain after the formation of the gumbotil, Lake Calvin was eventually 

 tapped and drained. 



Eead by title. 



PHYSIOGRAPHY OF THE PAR I A RIVER VALLEY, SOUTHERN UTAH 



BY RAYMOND C. MOORE 



i Abstract) 



Paria River is one of the main tributaries of the Colorado in southern Utah, 

 its course trending south-southeast from the border of the high Tertiary pla- 

 teaus to the head of Marble Canyon at Lees Ferry. The drainage basin of 

 this stream exhibits physiographic relations which are typically representa- 

 tive of a large part of the Colorado Plateau province. 



Essential factors in the shaping of land forms in the Paria Valley are the 

 semi-arid climate, the character and structure of the rock formations, eleva- 

 tion with respect to the master stream, and geologically recent changes in 

 elevation. Annual precipitation is small, but the rains are torrential and the 

 proportion of run-off is large. Canyons are a dominant topographic feature. 

 The rocks consist of alternating hard and soft divisions which are in the main 

 inclined to the north. About midway in its course the river crosses obliquely 

 a steep-dipping monoclinal fold, along which are developed prominent hog- 

 backs. A large north-south fault, with upthrow on the east, crosses the upper 

 part of the drainage basin. The hard strata produce escarpments and hog- 

 backs, the soft produce valleys and badlands. A difference in elevation of 

 more than 7,000 feet exists between the headwaters of some of the tributaries 

 and the mouth of the Paria. 



Analysis of the physiographic features of this interesting region permits 

 recognition of at least two erosion cycles belonging to late Tertiary and recent 

 geologic history, and, as noted by observers in some other parts of the plateau 

 province, there is indication of displacement by faulting at more than one 

 epoch. The plateau scarp west of the upper Paria Valley, which now has an 

 elevation of more than 2,000 feet above the valley, is on the downthrown side 

 of one of the large faults, the valley itself being in the upthrown block. 



Read ])y title. 



