Esmeralda County, Nevada.—Turner. 271 
The Recent or fiuntan Period. The deposits subsequent 
to the Pleistocene which may be considered as having formed 
in recent times, are the playas or dry lake beds, and the most. 
recent of the detrital fan material. Beds of dry lakes or playas 
cccupy the lowest portion of nearly all of the valleys in the 
county. Many of them contain valuable deposits of various 
salts. The playas of Teels marsh, Rhodes marsh, and the play- 
as of Coluinbus,and Fish Lake valleys, have been extensively 
-worked for borax which is still being produced from the last 
three localities. The piava of Big Smoky valley, locally known 
as the San Antonio marsh, shows a thin coating of an efflor- 
escence which consists largely of chloride of sodium, and the 
Clayton valley playa shows a thick white coating of choride of 
sodium over many square miles. 
During the Recent cr Human period many of the older 
alluvial fans have undergone elevation, and the waters of sub- 
sequent time have cut “washes” in them and spread the mater- 
ials out in the form of alluvial fans, but at lower altitudes than 
the older alluvial fans. These newer detrital materials are 
constantly being addeu to, the fresh material being distinguish- 
able from the older by its lighter color. 
At the south end of the Clayton valley is a considerable 
group of hills. composed entirely of wind-blown sand. This is 
said to contain a small amount of gold distributed through it. 
These dunes appear to have been formed in an eddy in the air 
currents, which sccm permanently to exist at this point. They 
shift about from \ear to year to a certain extent, but on the 
whole retain essentiaily at their present location. In some 
other valleys there are also sand-dunes. 
Structural Geology 
It has long been held that many of the Basin ranges owe 
their origin to uplifts along normal faults, the valleys repre- 
senting subsided areas. The evidence obtained by myself in 
the course of the field work confirms this view. Some of the 
steep slopes seem to represent ancient fault scarps, the origin- 
al fault surfaces heing tow largely removed by erosion. The 
vallevs are in purt certainly true rock basins, whose rims are 
composed of rocks older than the desert detritus. It seems 
apparent that the cnly way that such valleys can form is by sub- 
sidence. Although along the steep slopes which are here attrib- 
