138 REPORT UNITED STATES GEOLOGICAL SURVEY. 



wliicli breaks the force of the wind, there we find the greatest acciimii- 

 latioDS of sanil. It is carried thither, but the wind is forced to take an 

 iiinyard course, and much of the sand must fall. Near the Sweetwater 

 and Whiskey Gaps, and at Sandy Creek Pass, the fine sand is blown uj) 

 upon the hillsides for a distance of 500 to GOO feet. It is always found 

 most abundantly on those hills which i)resent a face to the soutiiwest. 

 Tlie southern slopes are covered with a thin layer, but upon them we 

 rarely find an accumulation of dunes. On account of the persistency 

 of the wind the upper portions of this sand are very loosely dei>osited, 

 aiul are constantly shifting. Aii animal in ijassing over it will sink in to 

 the knees. No vegetation can take hold on the dunes. At a few places 

 depressions were found in which the sand had somewhat hardened, and 

 sagebrush took advantage of these occurrences. 



From a distance the dunes resemble the waves of a "chopped" sea. 

 Sloping gently toward the Avest, eacli w^ave show^s a steep incline on the 

 opposite side. " Eipple-marks," not distinguishable in their form from 

 those i^roduced by water, cover the western slope. In very windy Aveathei" 

 a long-contiuued yellow cloud of dust may be seen along this "sand- 

 belt." It rises high into the air and dei)osits its sand in a line parallel 

 Avith the direction of the Avind. With but little motion of the atmos- 

 l)here the moA^ement of the dunes could be faA^orably studied. Eolliug 

 upward along the western slope of an indiAidual dune, the particles of 

 >saiid steadily adA^ance in iiarallel, successiA^e roAvs. lieaching the cap 

 of the Avave, each row^ rolls doAvn the eastern incline, there again to be 

 l)i(iked up and marched farther eastAvard. 



An interesting occurrence to us was the fact that many of the lakes 

 which AA^ere located in the immediate Aicinity of this series of dunes con- 

 tained Avater, Avhile those removed some distance from it AA'cre dry. I 

 explain this by assuming that the precipitated moisture, the quantity of 

 Avhich is small at best, can more readily soak into the sand and be re- 

 tained for a long time, preserved from CA^aporation. In thisAvay small 

 si)rings or underground water-courses can be formed, which will furnish 

 the lakes near by AAdtli a greater absolute quantity of Avater than those 

 leceiA^e which are dependent upon surface-drainage and direct precii)ita- 

 tion. Whether such springs remain CA^en only partially actiAe during 

 the entire summer is A^ery doubtful. The quantity of Avater AA'^hich is 

 <^aiTied into the lakes during the wet season is so much in excess, how- 

 CA^er, OA^er that which otbers recei\"e haAing the same drainage area that 

 it is not reduced to the same extent by eA'aporation. Another factor 

 here enters into consideration, the capacity for satuiation. While the 

 moisture which appears during the summer in the form of slight pre(;ipita^^- 

 tious, such as dew and brief showers, is mostly lost very rapidly by 

 evaporation, the peculiar physical conditions of the sand permit it to pen- 

 etrate to some depth. In this manner the supply of the lake is not 

 drawn upon by exhausted surrounding beds of the same level, and AviU 

 be diminished more slowly in consequence. 



As a necessary consequence of the vicinity of these lakes to the sand 

 area, we find considerable masses of quicksand along some of their shores : 

 Near Sandy Creek Pass a considerable number of lakes, of a^ arying sizes, 

 occur directly in the sand dunes. On account of the satm-ated condition 

 in which the sands haA'e here remained for a long period of time, they 

 could not be transported by the Avind wherever the grains AA'ere thus 

 bound together by moistiu-e. In consequence some soil was formed there. 

 Grassy A^egetation soon took advantage of this, and we now find some 

 very fine meadows bordering the lakes. Eising only a short distance 

 above their level, however, we are in loose sand once more. 



