MCGEE] CLIMATE OF SONORAN PROVINCE 23 



lying' ranges and biittes. The most conspicuous inequality of the slope 

 (partly because of its coincidence with tide-level) is ottered by the 

 rugged ranges of Serilaud. These may be considered four in number, 

 all approximately parallel with each other and with the coast; the first 

 is a series of eroded reninaTits (Cerros Anacoretos) from (500 to 1,200 

 feet in height; the second is the exceedingly rugged Sierra Seri, culmi- 

 nating in Johnson peak 5,000 feet above tide; the third is Sierra Kun- 

 kaak, attaining about 4,000 feet in its highest point; the fourth is 

 Sierra Menor, some 2,000 feet high, with the northern extremity sliced 

 oti' obliquely by marine erosion. The principal arm of Desierto Enci- 

 nas lies between the first two ranges, El Inflemillo separates the second, 

 and third, while a subdesert valley divides the third from the fimrth. 

 The valleys correspond more closely than the ranges; if the land level 

 were 100 feet higher the strait and its terminal bays would become an 

 arid valley like the others, while if the sea-level were 500 feet higher 

 the four ranges would become separate islands similar to Angel de la 

 Guarda and others in the gulf. 



The Sonoran province is notably warm and dry. The vapor-laden 

 air-currents from the Pacific drift across it and are first warmed by 

 condnction and radiation from the sun scorched land, to be chilled 

 again as they roll up the steeper roof-slope to the crest; and the precip- 

 itation flows part way down the slopes, both eastward and westward 

 from the Sierra Madre — literally the Mother (of waters) range. A 

 climatal characteristic of the province is two relatively humid seasons, 

 coinciding with the two principal inflections of the annual temperature- 

 curve, i. e., in January-February and July-August, respectively. In 

 the absence of meteorologic records the temperature and precipitation 

 maybe inferred from the observations at Yuma and Tucson,' which are 

 among the warmest and driest stations in America, or indeed in the 

 world; though it is probai>le I hat such points as Oaborca, Bacuachito, 

 and Hermosillo are decidedly warmer and perhaps slightly moister 

 than Yunui. The ordinary midday summer temperature at these points 

 may be estimated at about 110° in the shade (frequently rising .5° or 

 10° higher, but dropping 20^ to 50° in case of cloudiness); the night 

 temperature at the same season is usually 50° to 7.5°, though during 

 two-thirds of the year it is liable to fall to or below the freezing point. 

 The sun temperature is high in comparison with that measured in 

 the shade, the exposed thermometer frequently rising to 150° or 160°, 

 according to its construction, while black-finished metal becomes too 

 hot to be handled, and dark sand and rocks literally scorch unprotected 

 feet. The leading characteristic of the temperature is the wide diurnal 

 range and the relatively narrow annual range; another characteristic 

 is the uniformity, or periodic steadiness, of the maxima, coui)led with 

 variability and nonperiodicity of the minima. 



• The following monthly aud finniinl inetaorologic eximmaries, compiled from United States Weather 

 Bureau records at these stations, Itavi- beeu kindl.\' furnished l)y Prof. Willis L. Moore, Superintend- 



