982 REPORT OF NATIONAL MUSEUM, 1895. 



which partially filled the earlier canyons of the Pacific Slope. After 

 the deposition and subsequent elevation of the mesa sandstones, which 

 are assumed to be of late Tertiary age, there must have been a long 

 period of erosion, during which the interior valley was carved out and 

 drained through the deeper canyons running to the Pacific Ocean. 

 This was apparently followed by an extensive submergence of 2,000 

 feet or more, since wliich time the whole peninsula has been gradually 

 rising by periodic movements, with considerable base leveling in the 



intervals. 



" The present elevation of the mesa-topped ridges of the western 

 range indicates a base leveliug of the region at an elevation of about 

 2,000 feet above present sea level. This might have filled up all the 

 outlets of the interior region across the western range and admitted 

 of the inclosures of a body of water up to that level; but to account 

 for the present position of the deposits on the eastern side of the 

 valley, it is necessary to assume a subsequent dift'erential movement 

 by which that side has been raised a few hundred feet more than the 

 eastern side." 



EASTERN RANGE. 



" The older or buried eastern range is made up of granite and gneiss, 

 with highly altered sedimentary strata flanking it on the northeast, 

 which stand either vertical or with a steep dip to the eastward and 

 strike about northwest, or somewhat more to the west of north than 

 the general trend of the peninsula. The present divide, on the other 

 hand, follows the general trend of the coast line at a distance of 10 to 

 15 miles from it, and is marked in general by abrupt escarpments along 

 the eastern edge of the desert plain. 



"To the north of the limits of the field of observation, beyond the 

 thirtieth parallel, the summits of the older range have been planned 

 off and their depressions so evenly filled up by the more recent deposits 

 that they play no part in the present topography of the country. To 

 the south, however, where, east of the present divide, they have been 

 denuded of the more recent deposits, or still farther south, where they 

 were never completely covered by these deposits, they form conspicu- 

 ous and striking topographical features, in marked contrast with the 

 prevailing horizontal lines and broad shallow valleys of the western 

 portion of the peninsula. 



" In the northern region the desert plains and flat-topped ridges of 

 mesa sandstones risevery gently from the west to the divide line, which 

 almost invariably presents an abrupt escarpment to the east, over- 

 looking a region deeply scored by narrow gorges several hundred feet 

 in depth, with almost vertical walls. Here the divide line is marked by 

 occasional isolated table topped buttes, capped by rhyolite, which rise 

 500 to 1,000 feet above the desert level and serve to mark the original 

 level of the mesa sandstones, which have been protected from erosion 

 by the cap of more enduring rock. These rhyolites are generally of 



