ACADEMY OF SCIENCES] BASIN RANGES 245 



eastward; but the wisps usually vanish by evaporation in the dry lower air before they reach 

 the desert plains; it is only when a great atmospheric overturning causes a violent but local 

 thunderstorm that the lower ground is made "wet enough to run," and supply the torrents 

 which Gilbert described as roaring along the dry channels — true "wadies" — of the plains. 

 As the range is nearly everywhere barren, outcropping ledges are abundant. Near the crest 

 there are occasional good-sized pines and firs ; where springs occur in the uplands, they are 

 marked by copses of green aspens, which stand at the focus of many converging paths worn by 

 wandering herds of horses and cattle driven up the mountain for pasture by the neighboring 

 stockmen. The streams are mostly intermittent and wither away on approacbing the moun- 

 tain base. Some of them are subject to a well-marked diurnal variation of length; evaporation 

 during the hours of glaring sunshine compels them to shrink back into the rocky shelter of the 

 upper glens and the cool shade of the high-level aspens ; only after sunset do they, nymph-like, 

 venture down the great ravines to the rocky notches at the mountain base; there they sing all 

 night long a gleeful little serenade, as if to welcome the traveler who at the end of a fatiguing 

 day on the shadeless desert plains toils up the tiresome slope of a piedmont fan to wait for their 

 descent. By morning they have run out a short distance on the gravelly slope; but the parch- 

 ing heat of the day soon causes them to retreat to their mountain fastnesses again. 



THE WESTERN FACE OF THE HOUSE RANGE 



Gilbert approached the House Range from the north and followed its western escarpment 

 southward, making ascents to the crest at various points and finally crossing to the eastward. 

 He found the range to consist in the main of Cambrian sandstones and limestones with some 

 shales, dipping eastward for the most part, but turning northeast and southeast at the lowering 

 ends; the mass was discovered to be divided into seven or more blocks by transverse vertical 

 faults of moderate or small displacement, and these structural features were generalized in a 

 diagram, here reproduced in Figure 17, showing the range as seen from a point north of the 

 middle of White Valley; the southernmost part is foreshortened to too small a length. The 

 dissection of the northern part is described as so far advanced that its preuplif t form was not 

 detected there; but the highland of its southern part, although trenched by deep valleys, is said 

 to be an east-dipping peneplain. The contrast between the more gradual eastern slope and the 

 bold western face is repeatedly emphasized. The base of the western face is gently sinuous, 

 but no distinct facets were found on the spur ends. Nevertheless it is held that only the modern 

 uptilting of a great block of the earth's crust can reasonably explain such a moimtain range. 

 The fault along the western base is, however, not treated as a simple fracture; many fragments 

 or small blocks of the great uplifted mass, seen along its western base, are regarded as due to 

 step faulting: 



The irregular and sporadic inclined and downthrown blocks on the W face of the House range may be re- 

 garded as details of the great fault, a fault of which the minimum measure is . . . not less than 6,000 feet. 



The possibility of a secondary origin for some of the small blocks is noted : 



Some of the dropped masses along the front of Belt [a division of the range, south of its middle, limited 

 by transverse faults] may be landslips. 



This recalls the suggestion made above as to the origin of certain landslides on the 

 Wasatch front. It should be noted that, in so far as the transverse faults in the House 

 Range are concerned, their steep or vertical attitude suggests that they are due to forces of 

 unequal uplift in the upheaved block, and not to the extensional forces by which the block 

 was upheaved. 



While the northern part of the range was under examination and its bold scarp was in 

 view it was concisely described as — 



a conspicuous example of uplift along a fault — as distinguished from survival from erosion. It is incredible 

 that the erosion of White valley [the intermont depression to the west] should have left this great facade. The 

 time consumed in developing such breadth of valley [10 or 15 miles] would have sufficed also to give the moun- 

 tain a mature topography — unless the final work of erosion was at the mt. base and very deep. The many 



