418 J. K.MILLS ROCKS OF THE SIERRA NEVADA OF CALIFORNIA. 



Axes of greatest Uplifting. — A prevailing geographic characteristic of 

 the range is that the crest of each of its two great divisions and of its 

 individual mountains is near the eastern edge of the mass; in other 

 words, the easterly slope is much steeper than the westerly one. The 

 easterly slope may be called a fault-plane, though it is not by any means 

 a simple plane, hut a broken, jagged and irregular composite plane. The 

 western slopes also rise in part, if not wholly, by faults : but they are. as 

 a rule, of less shear, and form less prominent escarpments than those of 

 the easterly slopes. This is not, however, a universal rule. The westerly 

 slope of Grizzly ridge, for instance, rises from its foot by a fault, which I 

 have called the Cromberg fault, which can be traced and measured by 

 the dislocation of Tertiary deposits for over seven miles, and near the 

 hamlet of Cromberg, on the Middle fork of Feather river (in sections 12 

 and 13, T. -i:\ N., R. 11 E., M. I). M.), the uplift is more than 1,100 feel 

 vertically in 3,375 feet horizontally; bow much more than 1,100 feet I 

 cannot say, as the floor on which the Tertiary deposits rest at the down- 

 thrown (southwestern) side of the fault is not exposed. 



Relativt vertical Descent of eastern and western Slopes. — The descent of the 

 eastern slope of the range as a whole is much less in vertical extent than 

 that of the western slope; for the interior basin, at the foot of the steep 

 easterly fare, is much higher than the valley of California, at the foot of 

 the westerly slope. The elevation above sea-level of Owens lake, at the 

 foot of the easterly face, nearly east of the summit of mount Whitney 

 and 12 miles distant from it. is 3, (lis feet,* while Visalia, in the valley 

 about 54 miles west of the summit of mount Whitney, is but 34S feet 

 above sea-level.f Lake Tahoe is. according to Wheeler, 6,202 feet above 

 sea-level, while the summit of Twin peak, about four miles away, is 8,82 1 

 feet, and the valley 54 miles west of Twin peak is 163 feet above sea- 

 level. 



Strike and Dip. — The metamorphic sedimentary rocks of the range are 

 tilted to high angles with the horizon. The prevailing strikes arc parallel 

 to the general trend of the range and of the coast : the prevailing dips 

 are between 40° and vertical, and the Larger part of them between 60° 

 and vertical. The direction of dip over much the larger part of the area 

 is easterly; but in the northerly part of the eastern division of the range, 

 namely, on Grizzly ridge, Hough mountain, and northward to the edge 

 of the lava held, the prevailing direction is westerly, and north of the 

 North fork of the Feather this direction of dip extends further westward. 

 Unconformity of the Mesozoic and pre-Mesozoic. — The strike and dip are 

 but slightly affected by the Tertiary and Quaternary uplifting, and I 



*Capt. Geo. M. Wheeler, U. S. Geographical Surveys West of the 100th Meridian, 

 f U. s. Signal ( ifflce Reports. 



