110 



University of California Publications. 



[Geology 



remnant. Genoa Peak also rises nearly 700 feet above the some- 

 what dissected plateau remnant upon which it stands. But this 

 peak is clearly in a triangular fault-block which appears to have 

 been elevated relative to the surrounding blocks. The nearby 

 summits, however, are not so situated. The plateau elevation 

 here is about 8,300 feet, and the elevation of the larger summits 

 outside of Genoa Peak is a little over 8,800. The elevation of the 

 plateau remnants is taken in all cases as marked by the striking 

 subsequent stream channels thereupon. The difference in ele- 

 vations is thus constantly between 500 and 600 feet, irrespective 

 of the nature of the rock. If we assume for the moment the 

 hypothesis of an erosiona! surface, the possibility of crustal tilt- 

 ing at the time of the uplift initiating a new cycle of erosion 

 must not be overlooked. This places the question upon the 

 broader grounds of the larger elements of range history. So far 

 as the writer knows, the tilting of the range other than that east 

 and west has been inappreciable. This statement does not include 

 the movements of small blocks. If this be so, there is nothing 

 inharmonious between the hypsometric range and a possible old 

 surface peneplanation. The second test adds to the strength of 

 this conception. The summits are characteristically flat-topped, 

 with gently curved slopes connecting the plateau below. A 

 residual hill or monadnock would present a smoothly rounded 

 summit, unless there were a structural control by the differential 

 weathering of the rocks. There has been no such control, so that 

 the idea of monadnoeks has little weight. The writer adopts, 

 therefore, the hypothesis of an older erosional surface than the 

 high plateau. This is not in accordance with Professor Lawson's 

 conclusions, but serves to bring into greater relief the need for 

 more investigation. 



II. The High Plateau. 



The best remnants of the high plateau are near Little Val- 

 ley. The largest of these is at Marlett Peak, and is a splendidly 

 preserved area. Marlett Lake exists over the site of a down- 

 dropped block of the same surface. One comes into a different 

 land after toiling up the surrounding steep fault-slopes. Traces 

 of this same remnant are found along the ridge that strikes 



