456 University of California Publications in Geology [Vol. 7 



lake deposits for twenty-five to thirty miles above the resistant 

 rim. The stream is undoubtedly still cutting in its narrow 

 vertical-walled gorge through the hard rocks, and meanwhile it 

 has locally widened its trench in the unresistant lacustral beds 

 and fanglomerates above the gorge to a width of a half mile or 

 more, as at Camp Cady. 



Evidence of Climatic Change in the Manix Region in 

 Pleistocene Time 



The quantity of water brought to the Manix region by the 

 Mohave River of today is in striking contrast to the supply fur- 

 nished by that stream during Manix Lake time. The present-day 

 Mohave River is dry throughout much of its lower course during 

 most of the year, and its spasmodic floods yield only sufficient 

 water to fill temporarily a playa lake of small area compared to 

 that occupied by Manix Lake deposits. The playa lake is reported 

 to be dry all but a few days or weeks of each year. The Mohave 

 River of Manix Lake time afforded water for the two hundred 

 or more square miles of continually evaporating surface of Manix 

 Lake, with sufficient overflow for the lake to retain its freshness. 

 The mean annual flow of the Mohave River has apparently greatly 

 decreased. 



It is improbable that such causes as diversion of headwater 

 tributaries of the Mohave or decrease of altitude influencing pre- 

 cipitation of the San Bernardino Mountains watershed brought 

 about the lessened flow. The decreased flow apparently indicates 

 a decrease in the general precipitation of this and adjoining 

 regions since Manix Lake time. What relation such change of 

 climate may have had to possible Pleistocene uplift in the San 

 Bernardino and other high mountain ranges to the west, or to 

 post-glacial changes of climate, cannot be stated in the absence 

 of more complete knowledge. 



Summary 



In Pleistocene time the waters of the Mohave River were 

 ponded in a basin in the eastern Mohave Desert region. In the 

 lake thus formed there was deposited a series of clays and 



