PLEISTOCENE CLIMATE AND ITS INTERPRETATION 549 



parison, and by the fact that the topography of the basins has changed 

 very little since the ancient strands were formed. 



The range in humidity (or aridity) among the various basins in the 

 Pleistocene epoch was apparently as great as the difference in a given 

 basin between the Pleistocene and the present. A considerable number of 

 the closed basins in the province were too arid in the Pleistocene to con- 

 tain lakes of any consequence, whereas a few are humid enough at present 

 to contain perennial lakes of considerable size. The relatively humid 

 parts of the province at the present time seem to be comparable to the 

 most arid parts in the Pleistocene epoch (compare figures 1 and 2). The 

 region of southwestern New Mexico and southeastern Arizona in the 

 Pleistocene is apparently comparable to southern Oregon at present, for 

 the Pleistocene lakes near the Mexican border do not seem to amount to 

 much more thaii do the present lakes of Oregon. The south end of Ne- 

 vada in the Pleistocene can perhaps be compared to northeastern Nevada 

 at present, with its few small lakes, the difference in latitude here being- 

 less than in the first case because there is a great difference in altitude. 

 Parts of southeastern California and trans-Pecos Texas in the Pleistocene 

 can perhaps be compared to parts of Nevada at present where the climate 

 is just too and for perennial lakes. Lastly, the Pleistocene lakes of the 

 somewhat dismembered Death Valley basin, including the Owens, Amar- 

 gosa, and Mohave Eiver drainage basins, seem to have their approximate 

 counterparts in the existing remnants of Lake Lahontan. 



These generalizations are, of course, interesting rather than accurate, 

 but they suggest a somewhat tangible method of attack. That they in- 

 volve a substantial difference in climate is shown by the fact that in each 

 of the four comparisons that have been made there is at present a differ- 

 ence in mean annual temperature between the regions compared of more 

 than 15 degrees Fahrenheit. What is needed for even an approximate 

 solution of the problem is adequate topographic maps of the basins, a 

 general knowledge of their rock formations and structures, complete 

 maps and data regarding their Pleistocene and present lakes and their 

 present areas of ground-water discharge, adequate data as to the physio- 

 graphic changes that have taken place in them since the Pleistocene, and 

 abundant records of their temperature, precipitation, stream flow, evap- 

 oration, and ground-water discharge. 



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