10 University of California Publications in Geology [ VoL 11 



POSSIBILITY OF DIFFERENT PERIODS OF GRANITIC INVASION 



It may be that the continuity of granite from the Sierra Nevada 

 into the Coast Ranges is only apparent, and there are really two dis- 

 tinct periods of plutonic activity in the two regions. 



As will be indicated below, certain paleontologists do not agree 

 that the Knoxville belongs entirely to the Lower Cretaceous, but are 

 inclined to correlate the lower Knoxville with the Upper Jurassic 

 Mariposa, and place the upper Knoxville in the Lower Cretaceous. If 

 this be correct, then it follows that the two granites cannot be of the 

 same age, but the granite of the Coast Ranges must be the older. 



It is possible that the Coast Range granite is a product of the same 

 cycle of events that produced the granite of the Sierra Nevada. We 

 may imagine that the intrusion was a progressive process which began 

 in the northern Coast Ranges and gradually spread southward and 

 around into the Sierra Nevada. However, the proximity of the Fran- 

 ciscan to granite masses in the San Emigdio Range in the southern 

 Coast Ranges is opposed to this. Nowhere does the Franciscan show 

 any evidence of intrusion by granite ; it always shows evidence of 

 being derived in large part from granite. 



It is also possible that the Coast Range granite is a separate and 

 independent intrusion and has no relation to anything in the Sierra 

 Nevada. In this event, as far as stratigraphic relations are concerned, 

 the Franciscan group might be Jurassic, Triassic, or even earlier. 

 The fossil evidence, however, limits it to the Mesozoic. 



The presence in the Sierra Nevada of an older granite intruded 

 at the end of Carboniferous time, suggests another way out of the 

 difficulty. 19 The Coast Range granite may belong to the earlier 

 period and there may be no equivalent of the post-Mariposa granite 

 in the Coast Ranges. In the southern Sierra Nevada the granite may 

 belong to the earlier period and this older granite may be the one 

 which can be traced into the Coast Ranges. It should be pointed out, 

 however, that the whole of the granitic area of the southern Sierra 

 Nevada cannot be pre-Mesozoic. The Mineral King belt of rocks is in 

 part Triassic 20 and the granite in which it lies is post-Triassic. 



is The presence of this earlier granite in the Sierra Nevada has been 

 referred to in several of the Gold Belt Folios of the United States Geological 

 Survey. 



20 Turner, H. W., Rocks of the Sierra Nevada, 14th Ann. Rep., U. S. Geol. 

 Surv., pt. 2, p. 451, 1892-93. 



