POST-QUATERNAEY DEPOSITS. 155 



Another area of drifting sand occurs to the southward of the Carson 

 Desert and covers portions of Alkah Valley and the desert basins south of 

 Allen's Springs. This train of dunes commences somewhat to the eastward 

 of Sand Spring Pass, at the east end of Alkali Valley, and may be traced 

 westward for at least twenty miles to the mountains on the east side of 

 Walker River Valley. The width of the belt is not more than four or five 

 miles. In a sheltered recess in Alkali Valley, a mile or two northwest of 

 Sand Springs, the sand has been accumulated by eddying wind-currents so 

 as to form a veritable mountain, rising, by estimate, two or three hundred 

 feet above the plain. This ever-changing mountain of creamy sand varies 

 its contours from year to year, while every zephyr that blows is busy in 

 remodeling the rounded domes and gracefully curving crests and in alter- 

 ing the details of the tracery that gives grace and elegance to the structure. 

 The dunes in this train, like those northward of Winnemucca, are traveling 

 eastward across mountains and deserts and seem little afiFected in their 

 ultimate course by the topography of the country. In the desert valley 

 south of Allen's Spring the sand is carried up the steep eastern border of 

 the basin and finds temporary resting places on the terraces cut by the 

 waves of Lake Lahontan in the black basalt of its shores. The yellow 

 sands loading these ancient terraces bring out the horizontal lines in strong 

 relief by reason of their contrast in color and accent the minor sculpturing 

 of the cliffs. 



Another region of sand dunes covering an area a few square miles in 

 extent is located at the southern end of Winnemucca Lake and threatens 

 to obstruct the only stream that supplies that water body. 



It is impossible to trace the sands forming these varioiis dunes to their 

 sources, but we. may be sure that they have traveled far and were not 

 derived from the waste of the rocks in their present neighborhood. Similar 

 areas of drifting sand occur at many localities throughout the region west 

 of the Rocky Mountains, a number of which are known to be traveling in 

 the same direction as those of the Lahontan basin. It is possible, as has 

 been suggested by previous writers, that these various areas all belong to 

 a single series, and are formed of the beach sands of the Pacific which have 



