414 The University Science Bulletin. ^ . 



surface "waters. 



Though the topography of southern Utah is very evidently the 

 result chiefly of erosion by running water, there are few perennial 

 streams in the region. The Colorado, master stream of the plateau 

 country, gathers the waters from the west slopes of the Rockies, 

 from the Uintas and other ranges where rains and melting snows 

 furnish a varying but unending water supply. The tributaries 

 which unite to form the Colorado begin, for the most part, as clear 

 mountain streams, but in southern Utah the river carries so heavy 

 a load of mud and sand that the water is dark reddish brown. On 

 this account the name Colorado was first applied. The river is 

 large and swift, with swirling eddies and numerous rapids. The 

 only permanent tributaries to the Colorado in southern Utah are 

 San Juan river on the south and Dirty Devil and Escalante rivers 

 on the north. Each of these streams flows in a deep canyon, and, 

 except for size, is essentially similar to the Colorado. The Esca- 

 lante, which is the main stream in the region from which most of 

 the collections of insects were obtained, is fed by the melting snows, 

 rains and springs of the southern extremity of the highest of the 

 plateaus, the Aquarius. Its waters are somewhat clearer than those 

 of the other streams, because most of its course lies through massive 

 sandstones. 



The numerous smaller streams in southern Utah contain water 

 only at times of local rainfall. The run-off is very rapid, and after 

 a torrential, muddy flood of less than an hour, or at most a few 

 hours, the flow ceases. This type of swift, intermittent streams is 

 characteristic of all the plateau region. 



After rains there are in places pools or "tanks" in such natural 

 hollows as may retain any of the water. Some of these are found 

 in the stream channels, others in eroded depressions in the nakecf 

 rock. Some are small, shallow and short-lived under the rays of 

 an intense sun and a thirsty atmosphere; others are larger, and 

 occasionally deep. Those in the channels of streams commonly 

 contain very muddy water, which, because of the excessive fine- 

 ness of the mud, retains the sediment in suspension until evapora- 

 tion gradually gives it the consistency of thick soup or gravy, and 

 finally of brick. Where the rain water accumulates in sandstone, 

 or where the gathering waters do not cross exposures of the soft 

 shales which furnish most of the muds, the waters remain fairly 

 clear. The larger "tanks" may retain water from year to year, 

 shrinking slowly through times of drought, but refilling on the 



