GEOGRAPHICAL FEATURES OF THE CAHUILLA BASIN. 



Bt Godfrey Sykes. 



GENERAL DESCRIPTION. 



Although the extensive arid area of southeastern California is strikingly homo- 

 geneous in its general physical features, it has nevertheless been nominally divided, for 

 purposes of local convenience and geographical distinction, into certain definite districts 

 or deserts, and the Cahuilla Basin, with its associated drainage, lies almost entirely within 

 the confines of the most southeasterly of these subdivisions — the Colorado Desert. This 

 name was first applied to the region by the late Professor Blake, as narrated elsewhere in 

 this volume, and it has since come into very general use. 



As now defined, the Colorado Desert may be considered to include the area between 

 the Coast Range on the west and southwest; the Colorado River on the east; the San 

 Bernardino and Chuckawalla Mountains on the north; and to merge, without any very 

 definite limits, into the eastern bajadas of the Peninsula Mountains to the south — some 

 8,000 square miles in all. (Plate 2.) It lies mainly within the United States, but its southern 

 portion extends across the international boundary-line into the Mexican State of Baja 

 California. It is traversed near to its northern limit, in a southeast to northwest direction, 

 by the main line of the Southern Pacific Railroad, and within the last decade or so several 

 subsidiary lines have been built to serve the growing needs of the prosperous communities 

 which have sprung up upon the irrigable lands of the Imperial Valley. 



Topographically the Colorado Desert is divided into two main and parallel basin 

 areas which merge at their southeastern extremities in the alluvial plains of the Delta of 

 the Colorado and are separated elsewhere by the Cocopah Range of mountains. 



The Pattie Basin, which is the smaller and most southerly of the two, lies almost 

 wholly within the Republic of Mexico. It has not as yet been fully examined or described, 

 but we know that its central and lowest portion is occupied by a fluctuating lake or lagoon, 

 fed by overflow from the lower Colorado, and it is probable that the bottom of this depres- 

 sion is many feet below sea-level. 



The basin to the north and northeast of the Cocopahs, which constitutes the main 

 portion of the Colorado Desert, and to which the name Cahuilla Valley was given by Professor 

 Blake, has the general form of an acute-angled scalene triangle — the west bank of the Colo- 

 rado River forming its base; the Cocopah, Superstition, and Santa Rosa mountains its 

 southern side; and the gradually converging line of the Chocolate, Chuckawalla, and San 

 Bernardino Mountains its northern side. The apex of the triangle lies at the summit of the 

 San Gorgonio Pass, between the San Bernardino and San Jacinto Mountains. (Plate 7.) The 

 extreme length of this triangle is about 185 miles and its width at the base about 75 miles. 



The floor of the basin is roughly spoon-shaped, gradually dropping from its south- 

 eastern end for a distance of about 140 miles until it has attained a depth of 265 feet 

 below sea-level, and then rising with increasing rapidity until at the summit of the San 

 Gorgonio Pass it has risen to an elevation of some 2,500 feet above. An area of sand-hills 

 and gravel mesas toward the northeast and a piedmont district which lies between the 

 Superstition Mountains and the main escarpment of the Peninsula Range, complete the 

 area under consideration. 



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