TOPOGKAPHIC FEATUEES OF THE DESEET BASINS. 33 



THE MONTE CRISTO BASIN. 



East of the Soda Springs Trough and surrounded by the Monte Cristo, Pilot, and 

 Cedar Mountains, lies the Monte Cristo Basin. Its lowest divide is in the gap between 

 the Cedar and Monte Cristo Mountains and is but little over 300 feet above the bottom 

 of the valley. This divide is not alluvial, but there are some indications of recent 

 movement and it is not impossible that this pass was once lower and the locus of an 

 outflow into the Big Smoky Valley. The area of the basin is but 300 square miles, 

 and, whether it overflowed or not, it is too small to be of great importance. Its deepest 

 depression is now covered by loose blown sand. 



THE COLUMBUS BASIN. 



South of the Soda Springs Trough is the north-south trough of the Fish Lake Valley, 

 all of which drains freely northward to the playa called the Columbus Salt Marsh 

 and occupying the extreme northern end of the trough. The stream which occupied 

 Fish Lake Valley has lost much of its vigor and a number of more or less saline marshes 

 and playas have been left along its course. All of these are recent and unimportant. 

 The lowest pass through which a discharge from the Columbus playa would be possible 

 leads into Khodes and the Soda Springs Trough, but the divide is nearly 500 feet above 

 the playa, and there is little probability that discharge actually took place over it. 

 The basin has almost certainly been an inclosed one during and since the Lahontan 

 period. There is a system of strand lines of usual character, the highest about 150 

 feet above the flat. The present drainage area of the Columbus is quite small, but 

 including the part of the Fish Lake Valley recently tributary to it, though now cut 

 off, it equals 1,350 square miles. The Columbus playa is about 50 square miles in 

 area. 



THE CLAYTON OR SILVER PEAK BASIN. 



The Clayton or Silver Peak Basin occupies a rather irregular structural depression 

 just east of the Fish Lake Valley. Its lowest pass being 650 feet above its bottom, 

 there is reasonable certainty that it never overflowed, though there is no satisfactory 

 direct evidence that it formerly contained a lake. Its bottom is a very saline playa 

 with many crusts and layers of common salt, both on the surface and in the clays below. 

 The area of the playa is about 30 square miles and that of the basin about 550 square 

 miles. 



THE BIG SMOKY BASIN. 



Eastward of Gabbs Valley and the southern end of the Dixie Valley lie three parallel 

 north-and-south troughs, of which the outer two slope and drain southward, while the 

 middle carries the northward-flowing stream of the Eeese Kiver. Toward the south 

 the central trough and its limiting ranges pinch out and the two outer troughs merge 

 into a much broader valley which continues to slope southward. These two outer 

 troughs and their southward extension form the Big Smoky Basin. The whole has 

 suffered greatly by stream decay, with the formation of many local playas and the cut- 

 ting off by alluvial dams of the extremities of both of the northern troughs. The 

 deepest depression of the basin is in the extreme southwest corner and is a playa of 

 small salinity and somewhat diversified by small dune areas. 



Just west of this playa between the Silver Peak and Monte Cristo Ranges is a pass; 

 scarcely 200 feet above the playa and leading into the Columbus Basin. The di-ain- 

 age area of the Big Smoky seems great enough to have filled the depression during- 

 the Lahontan period to a depth greater than 200 feet, but there is no evidence of dis- 

 charge over this pass, and the highest of a system of lake terraces which surrounds 

 the present playa is below the level of the pass. It is probable, therefore, that the 

 Big Smoky did not overflow. 



19750°— Bull. 54—14 5 



