722 



SCIENCE. 



[N. S. Vol. XXIII. No. 593. 



city toiiehed Tinajas Altas as the sole 

 permanent 'water' in the 125 hard miles 

 between Rio Souoyta and Rio Colorado — 

 i. e., in 'El Camino del Diablo' which in 

 the more fertile valleys of California be- 

 came 'El Camino Real'— and ever since the 

 supply has been deemed unfailing; though 

 singularly enough the water was prac- 

 tically exhausted in the summer following 

 the exceptionally wet winter and spring 

 of 1905, seemingly for the reason that the 

 unusually prolonged and gentle precipita- 

 tion served rather to fill the tinajas with 

 sand than to sweep them clean and leave 

 them brimming, as do the ordinary rains 

 of the region. 



By trail the locality is 75 miles south- 

 east of Yuma, by air-line 15 or 20 miles 

 less; it is 35 or 40 miles south of Gila 

 River at its southerly bend east of Gila 

 City, and 40 or 50 miles north of the 

 nearest shores of Gulf of California; the 

 closest habitations are at the Southern 

 Pacific station Wellton, some 30 miles away 

 in an air-line, and more by any practicable 

 route— there is no road. 



The altitude of the lowest tinaja and the 

 adjacent mesa on which the station was 

 established is about 1,400 feet ; the contigu- 

 ous gorge-walls and peaks rise precipitous- 

 ly 750 feet, and some of the neighboring 

 crests 2,000 feet higher (the United States 

 and Mexican boundary survey maps locate 

 near-by peaks above the 800-meter contour 

 line). Albeit a low range. Sierra Gila is 

 notably rugged and conspicuously sterile 

 — it is, indeed, one of the most utterly 

 barren mountain masses in America, From 

 its western base a sandy plain, broken by a 

 few low buttes and ranges, stretches south- 

 westward to the Coeopa Mountains far be- 

 yond the Colorado, inclining southward to 

 the gulf; east of it lies a smooth valley- 

 plain seven to twelve miles wide, bounded 

 beyond by a parallel granite range— Sierra 



de la Cabeza Prieta. Still further east- 

 ward lie other more or less parallel ranges 

 M'ith intervening valleys; the Mohawk 

 Range, Sierra Pintada, Sierra Pinecate (on 

 the Sonora side), A jo Mountain, Sierra 

 Quijotoa and the Baboquivari being the 

 more conspicuous elevations aboiit which 

 summer clouds are wont to gather. 



The station equipment comprised (1) 

 a weather bureau instrument shelter of 

 the type used by 'volunteer observers' 

 (mounted on a base about four feet high, 

 improvised from the packing-crate and 

 grub-boxes and guyed with baling-wire) ; 



(2) maximum and minimum thermometers; 



(3) a sling psychrometer ; (4) a barograph 

 (supplemented by a fine aneroid of French 

 make) ; and (5) an improvised rain gauge. 



OBSERVATIONS AND GENERALIZATIONS. 



Observations were made and recorded 

 twice daily, viz., 8 a.m. and 8 p.m. local 

 time; the hour of observation being ad- 

 vanced some minutes (in accordance with 

 suggestions growing out of hourly obser- 

 vations during the earlier days) to counter- 

 balance the effect of the local topography : 

 for the station occupied a deep gorge open- 

 ing east-northeastward in which the rays 

 of the morning sun were concentrated by 

 reflection, while the afternoon sun set be- 

 hind Sierra Gila at 4 to 4:15 p.m. The 

 outfit reached the ground and the instru- 

 ments were unpacked during the afternoon 

 of May 20, and experimental observation 

 began on the morning of May 21 and was 

 well under way on May 23;- the observa- 

 tions were continued until after sunset 

 August 28, when the station was hastily 



' In the transcripts of the records and averages 

 first made, the period of systematic observation 

 was reckoned as beginning with May 23; but on 

 finding that the total period of observation was 

 exactly one hundred days reckoned from and in- 

 cluding May 21, the experimental record was 

 afterward incorporated. 



