340 University of California Publications in Geology [Vol. 8 



GEANULAB INTEUSIVES 



The granular rocks which occur as intrusives in the limestones 

 have been laid bare in irregular areas along the Cedar Mountain 

 Range. They consist chiefly of noncrystalline, medium and coarse- 

 textured granular rocks of the general mineralogical composition of 

 granodiorites. Locally orbicular structure has been developed in them, 

 and they are cut by pegmatite and aplite dikes. Although these 

 intrusive rocks are jointed, they do not exhibit the effects of intense 

 deformation seen in the sedimentary rocks which they intrude. 



LAVAS 



Lavas occur on both the higher parts and on the flanks of Cedar 

 Mountain. They consist of rhyolites, andesites and basalts. The 

 rhyolites are usually white in color, with occasional reddish tints. 

 Phenocrysts of quartz and biotite are quite abundant in these rocks; 

 hornblende occurs sparingly. The andesites present a variety of shades 

 of black, blue, and red. They are usually porphyritic, with ground- 

 masses of fine texture. Some masses, in which large angular fragments 

 of adjacent andesitic rocks are present as inclusions, appear to be 

 intrusive in the earlier andesitic flows and are of coarser texture. The 

 basalts are dense, bluish-black, fine-textured rocks, often exhibiting 

 columnar structure. 



Associated with the andesites are considerable thicknesses of vol- 

 canic agglomerates, the rough subangular masses in which range in 

 size up to twelve or fifteen feet in diameter and consist almost entirely 

 of andesite of various colors. A light-colored tuffaceous matrix makes 

 up but a small part of the agglomerates. There is little or no classi- 

 fication of the volcanic materials. It is probable that in part at least 

 the agglomerates were laid down in the form of mudflows. 



So far as observed, the outflow of the rhyolites preceded that of 

 the andesites. The basalts were extruded last. 



The relation of the lavas to the underlying Mesozoic limestones and 

 intrusives is that of a profound unconformity, which represents an 

 interval of time of sufficient length to permit intense deformation 

 of these older sedimentaries, intrusion by the granular rocks, and sub- 

 sequent erosion deep enough to expose these plutonic masses. The 

 bulk of the andesites and perhaps all of the rhyolites on Cedar Moun- 

 tain underlie the upper Miocene lake beds. While the lavas have not 



