1912] 



Baker: Western El Paso Range 



Ul 



Dissection of the Sierra Debris Slopes 



The distance from the exposures of bedrock on the southern 

 slopes of the Sierra to the base of the north flank of the El Paso 

 Range in the vicinity of Red Rock Canon and Ricardo post-office 

 is probably not greater than four or five miles. In the entire 

 interval between the ranges the alluvial surface slopes down- 

 ward to the south at an angle which averages about two degrees. 

 There can be absolutely no doubt that the debris of this slope to 

 within a mile to the north of Ricardo post-office has been derived 

 from the Sierra, for in its finer parts it is composed of dis- 

 integrated crystals of the Sierra granite and the larger angular 

 bowlders are fragments of this same granite. The alluvium has 

 a characteristic light brown color given it by the feldspars of 

 the Sierra granite. The alluvium, apparently originally spread 

 out rather evenly and in quite uniform thickness over the pene- 

 planed surface of the Rosamond series, has been dissected by 

 shallow gullies and valleys. Just north of the foot of the El 

 Paso uplift a rather broad basin has been excavated in this 

 alluvial mantle and the underlying Rosamond strata (pi. 9, fig. 1, 

 and pi. 10, fig. 2). Further north the debris mantle and the 

 lying Rosamond have been rather intricately dissected into a low 

 hummocky topography. Still farther to the north, near the 

 lower bedrock slopes of the Sierra, a much greater proportion 

 of the original debris-mantled upland surface remains, incised 

 at rather wide distances to only moderate depths by the main 

 drainage courses leading down from the Sierra Nevada, and 

 between these main drainage courses by smaller and shallower 

 gullies. In brief, the impression given the observer stationed on 

 the lower bedrock slopes of the Sierra is of a plane sloping rather 

 gently to the southward, the general smooth surface of which is 

 cut here and there by shallow gullies and valleys. 



A general uptilting to the northward of the surface of the 

 debris aprons or a depression of the Kane basin relative to the 

 country farther north would cause dissection of slopes formerly 

 at grade. Any change of climate which would increase erosive 

 forces could cause the dissection of this alluvium. Or it might 

 normally become dissected, without the interposition of uplift 



