CLIMATE AND FLORA. 493 



a considerable gap of unknown country from that described by Lindgren. 

 In this latitude the average elevation of the peninsula is about 2,000 

 feet, and that of its higher ridges may be taken at less than 3,500 feet. 

 It is a singularly arid region, having practically no running water on the 

 surface and very few permanent springs ; nevertheless our experience 

 has shown that properly located wells obtain a fair suppl}^ of water at 

 depths of 20 to 60 feet. The climate is remarkably equable and health- 

 ful, being but little warmer than that of the coast region of southern 

 California and as a rule much drier. The diurnal changes of tempera- 

 ture are, however, very great. It is swept by continuous breezes from 

 either coast, which appear to blow alternately about three days at a time, 

 those from the Pacific being laden Avith more or less moisture, while the 

 east winds are extremely dry. Like California, it has a rainy season in 

 the spring, but this is generally but of few days' duration and extremely 

 irregular and uncertain. 



The most striking feature to the traveller from the north is its peculiar 

 vegetation, which presents but few familiar species among a wilderness 

 of strange and Aveird forms. It consists mainly of thorny shrubs and 

 flowering plants, the few known representatives of which are found in the 

 dessert valleys of Arizona. Of leaf-bearing trees which might constitute 

 a protection against the i^owcrful rays of the noonday sun there is an 

 entire absence. A few isolated palms are found near some of the springs. 

 Varieties of mesquite and yucca are common along the bottoms of the 

 larger valleys. The most imposing plants are the giant cactus (supposed 

 to be the Cereus pringlei), which sends its branching shafts at times to a 

 height of 30 feet. The endless procession of these in some long valleys 

 resembles at a distance the relics of a burned forest. Among the infinite 

 variety of smaller cactus plants, the most vivid impression is retained of 

 the one known to the Mexicans as the "choya," which at the slightest 

 touch leaves a ball of spines sharper than a number 10 needle deeply 

 ])uried in the flesh. Agaves are most abundant next to the cactus, the 

 dried stems of the dead Agave shaivi being often thick enough to resemble a 

 nursery of 3'oung saplings. The most singular forms are what are locally 

 known as '' sirios " (Fauquier ia splendens and F. columnaris'), which often 

 send their bare branchless stems 30 to 40 feet into the air. More like a 

 tree is the low branching elephant tree (Veatchi cedrocensis), seldom more 

 than 10 feet high, whose bark is said to be used by the Mexicans for 

 tanning. 



This whole region may be in one sense considered to be a mesa region, 

 since at one time the present mesa formation extended from coast to 

 coast, but at the present day the mesas are no longer continuous, and 

 erosion has disclosed an underlying or buried topography whose general 



