380 



University of California Publications. [Geology 



filled the inclosed valleys with bowlders, gravels, and sands — debris from 

 the wasting mountains — and the process is still going on (pp. 40-42). 



As far as the continental area is concerned, the bases of 

 tentative correlations — aside from the Rosamond whose fossils 

 prove .its upper Miocene age — are the epochs of deformation, 

 volcanism, and erosion which appear to have been contempor- 

 aneous in that region and to have had as products sediments and 

 lavas of lithologic similarity. We do not as yet know the rela- 

 tions of the Rosamond terrestrial fauna with the marine faunas 

 of the southern Coast ranges, but the general age of the faunas 

 gives us a datum plane upon which a tentative correlation may 

 be begun, while diastrophic events in the two provinces seem to 

 be broadly contemporaneous. The long period of Fernando de- 

 position may be complementary to the first cycle of post-Miocene 

 erosion in the interior, as both of these processes seem to require 

 a fairly long period during which diastrophism was quiescent. 

 The present orography of the southern Great Basin has proba- 

 bly come into being as the product of mountain-making move- 

 ments of a date posterior to the later part of the Pliocene. 



SUMMARY 



The oldest rocks yet known in the western Mohave Desert 

 are metamorphosed sediments, intruded by later plutonics of a 

 general granitic composition. The gneiss and schist near the 

 town of Barstow possibly belong to the older series. The intru- 

 sive granitic rocks were in places laid bare by erosion and on 

 their eroded and weathered surfaces were laid down lavas and 

 thick series of arkosic sediments, named the Rosamond Series by 

 Ilershey. The lavas and sediments were in places contempor- 

 aneous. In the two widely separated exposures of the Rosa- 

 mond arkosic sediments in the Barstow syncline and in Red 

 Rock Canon, fossils of upper Miocene age were found. It is 

 thought to be most probable that an epoch of mountain-making 

 immediately preceded or was contemporaneous with the depo- 

 sition of the Rosamond, which apparently shows all the evidences 

 of its origin from nearby recently uplifted land areas. It is 

 also considered most probable that an arid climate, essentially 

 similar to that of the present-day Mohave Desert, prevailed 



