244 GROVE KARL GILBERT— DAVIS emimoim national 



[Vol. XXI, 



THE FISH SPRING RANGE 



On nearing the Fish Spring Range — the northern companion of the east-tilted House Range — 

 Gilbert first gained the impression that it had been uplifted in mass and tilted to the west, with 

 a fault along its eastern base; on closer approach it was described as consisting of four principal 

 blocks; after more detailed inspection, during which a number of sections were studied out, the 

 smaller complications of its structure were discovered: 



The Fish Spring range is far from being a simple monoclinal uplift, flexed at the west and faulted at the 

 east. It consists of a dozen or more large blocks, each lifted and tilted westward. They are separated by 

 faults and unequally uplifted. The uplift is greater at the south than north, and with an exception is greater 

 along the central axis than at the margins. Each block is traversed by minor faults in large number. In a 

 general way it may be said that this structure has originated from general stresses acting within the zone of 

 fracture and is the equivalent of folding and mashing in the zone of flow. It has originated in the upper part of 

 the crust. I see no way to discriminate in this case, the structures produced in the making of the present range 

 from the structures belonging to the older history of the region. 



It may have been the accumulation of such experiences as this that led him later to say, 

 in another connection : 



I am satisfied that all our results in geology are tainted by the tacit assumption of simplicity that does 

 not exist. 



A good number of sections were carefully studied here, evidently with the idea of determin- 

 ing faults within the range by the repetition of identifiable strata in the way familiar to geol- 

 ogists, rather than by the physiographic evidence, which, to some geologists at least, is less 

 convincing. 



The Confusion Range lies farther southwest and south and is at first separated from the 

 House Range by the broad desert plain of White Valley. Its northern part "has the aspect of 

 the Cedar, an old range worn down toward the roots, fringed by veneering and invaded by 

 graded slopes." Farther on "the aspect is different. The [eastern] front is bold and finally 

 mural. The alluvial reentrants finally disappear. The top is a remnant of an old peneplain, 

 truncating the structure." Here White Valley narrows as the Confusion Range approaches 

 the House Range; near their southern ends the valley is only 2 miles wide. 



THE HOUSE RANGE 



Gilbert's goal in this season of field work was, as above noted, the House Range, which he 

 had selected 30 years before as a typical example of an uptilted, fault-block mountain. Like 

 its many companions, it rises over intermont detrital plains which hereabouts stand at altitudes 

 of from 4,500 to 5,000 feet and, with the mountain ranges, constitute a characteristic part of 

 the Great American Desert; undoubtedly great, undeniably American, and unredeemably 

 desert. The range and its surroundings are well represented on the topographic map of Fish 

 Springs quandrangle, surveyed in 1908 and published in 1910 on a scale of 1: 250,000, with 100- 

 foot contours. The mountain mass is 40 miles in length, north and south, and from 5 to 10 

 miles in width; its crest is over 7,000 feet in altitude for 30 miles its length and has two summits 

 over 9,500 feet. A gradual descent is made to the east; an abrupt escarpment much dissected 

 by huge, steep-pitching ravines falls off to the west, with great piedmont fans of detritus out- 

 spread from each ravine mouth. Many Bonneville shore lines are lightly marked on the 

 fans, thus exhibiting the relation from which Gilbert had years earlier inferred that the region 

 had Jiad a long arid history before the brief humid epoch of lake expansion, and that the post- 

 Bonneville epoch was a very short-lived interval. 



Fig. 17. — Generalized frontal section of the House Range; from Gilbert's notebook, 1901. Low-lying frontal blocks are omitted. 



The range is high enough to receive light summer showers from the little wisps of rain 

 which lofty cumulus clouds not infrequently condescend to trail beneath them as they drift 



