48 BULLETIN 54, U. S. DEPAETMENT OF AGEICULTUEE. 



tions become sufficiently favorable. Down the west side of the delta 

 runs tlie so-called Kio Hardy or Hardy Colorado, which is fed by 

 seepages or direct channels from the larger river to the east. West 

 of the Cocopa Mountains and close to tliis Rio Hardy is a shallow 

 basin separated from the river only by a wide and flat plain of very 

 little elevation. In times of flood the Hardy sometimes covers this 

 plain and flUs the depression. On the retreat of the river there is 

 formed an inclosed lake known as Laguna Maquata. When low 

 it is quite saline, but the salinity is destroyed whenever a flood 

 recomiects it with the Hardy. 



The area of the Salton Basin can not be accurately computed 

 because of the character of the delta and the uncertainty in the posi- 

 tion of the divide across it. It is probably about 8,000 square miles. 



THE BASINS OF THE NEW MEXICO-TEXAS TROUGH. 



The central portion of New Mexico has a structure very similar to 

 that of the Great Basin. A somewhat warped and folded plateau has 

 yielded to great north-south fractures, producing parallel ranges and 

 trough valleys as in Nevada and California. The most prominent of 

 these troughs is that occupied by the vaUey of the Rio Grande north 

 of El Paso. This was' once a. series of separate basins or "bolsons," 

 but the divides have been cut by the river and the entire vaUey is 

 now essentially drained, though stream decay has recently created a 

 number of local and unimportant playas. East of tliis trough lies 

 another wliich, not possessing a vigorous through-flowing stream, 

 has not been cut down or kept clean, and contains the several inclosed 

 basms next to be discussed. 



THE OTERO BASIN. 



The middle portion of this trough is occupied by the Otero Basin, lying between 

 the Sacramento Mountains on the east and the San Andreas Mountains on the west. 

 The writer has published elsewhere ^ a report of a reconnoissance of this basin from 

 the present viewpoint, and it is necessary here only to review the essentials of the 

 topography. East and west the basin is limited by the high walls of the trough. 

 To the north it merges with the Gallinas highland and the Chupedera Mesa, both high 

 and certainly pre-Lahontan. At the southern end the divide is alluvial and though 

 apparently ancient, is probably less than 300 feet above the present deepest depres- 

 sion. It is quite possible that the basin has overflowed this divide and drained into 

 the Rio Grande, but there is no direct evidence of this, and the writer does not con- 

 sider it probable. In any case, a series of ancient strands about the present bottom 

 indicates an inclosed history of some duration. The present deepest depression is a 

 large and very gy|3siferous i)laya, the southern end of which carries a deposit of hydrous 

 sodium sulphate believed to be of secondary origin. There are several small local 

 playas of no importance. 



■ The most interesting and unusual feature of the basin is a great area of gyj^sum 

 dunes, south and east of the main playa. The study of these dunes has yielded con- 



1 Circular 61, liuro.au of Soils, U. S. Dept. of Agr. (1912). The reconnoissance was made iii the company 

 of Br. Ellsworth Uuntington. 



