So WARREN N. THAYER 



the mouth of which was on the coast somewhere between Cape 

 San Lucas and Cape Corrientes. 1 This cutting may have been 

 coincident with the elevation succeeding the downwarping or it 

 may have occurred at some indefinitely later time. It is certain, 

 however, that the depth of the gulf is not due alone to drowning by 

 the sea, but largely to stream-bed corrasion incident to elevation. 

 The maximum corrasion is estimated by Botsford to have been at 

 least 6,000 feet. 2 



On the peninsula, but four small streams cut the coast line of 

 more than two thousand miles. This is due to the fact that there 

 is little or no precipitation. There are extensive areas on the 

 peninsula where not a drop of rain has fallen in many years, which 

 are characteristically desert in aspect and condition, even to the 

 extent of supporting a fauna which apparently does not require 

 water. In striking contrast to these conditions is the Sierra Pedro 

 Martir, located in the northern part of the peninsula. This is a 

 high plateau remnant, forested with conifers, and threaded here 

 and there by small watercourses which flow through grassy and 

 even marshy meadows. 3 Here cactus and yucca give way to 

 conifers; and the horned toad and desert fox are replaced by moun- 

 tain sheep and deer. In short, the region is the habitat of a fauna 

 and flora akin to that found in the western mountains of the 

 United States. 



The reason for this change from desert conditions which exist 

 on all sides is to be found in the height of the area, which causes it 

 to receive considerable snowfall from December to April. The 

 water from the melting snow lies close to the surface of the un- 

 drained plateau during a large part of the remainder of the year 

 and gradually finds its way to springs scattered at lower altitudes. 

 This condition dies out gradually down the gentle slope to the 

 Pacific but ends abruptly at the scarp overlooking the gulf. 



On the mainland, east of the gulf, there are numerous short 

 streams which have their sources high up in the Sierra Madre 

 Occidental, and receive considerable water during the rainy season. 

 Many of these are dry during the greater part of the year, but are, 



1 Ordonez and Aguilera, op. cit., p. 52. 



2 Botsford, loc. cit. * North, Am. Geog. Soc. Bull., XXXIX, 544. 



