48 BULLETIN 54, U. $. DEPARTMENT OF AGRICULTURE. 
tions become sufficiently favorable. Down thé west side of the delta 
runs the so-called Rio 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 this 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 fills 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 
reconnects it with the Hardy. 
The area of the Salton Basin can not be accurately coiepaee 
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 valley of the Rio Grande north 
of E] Paso. This was once a series of separate basins or ‘‘ bolsons,” 
but the divides have been cut by the river and the entire valley is 
now essentially drained, though stream decay has recently created a 
number of local and unimportant playas. East of this trough hes 
another which, not possessing a vigorous through-flowing stream, 
has not been cut down or kept clean, and contains the several inclosed 
basins 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 
topegraphy. 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 gypsiferous playa, 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 gypsum 
dunes, south and east of the main playa. The study of these dunes has yielded con- 
1 Circular 61, Bureau of Soils, U. 8. Dept. of Agr. (1912). The reconnoissance was made in the company 
of Dr. Ellsworth Huntington. . 
