361 University of California Publications in Geology [Vol. 13 



numerous others of smaller dimensions cutting the old sediments north- 

 east of Cienaga Seca Creek and the undifferentiated schists south of 

 Santa Ana Canon; in fact, nowhere are there any considerable areas 

 entirely free from granites. Because of their complex relationships 

 to the altered sediments and to each other they afford many problems. 

 There may be two or more periods of intrusion, and in further describ- 

 ing the rocks special attention will be given to evidence supporting 

 this statement. It is unfortunate that the most positive evidence, sedi- 

 ments laid down on granite and intruded by another granite, is lack- 

 ing. Still there are several reasons for believing in intervals of some 

 importance. 



About two miles up Big Morongo Creek pegmatite dikes and inclu- 

 sions of schist in granite gneiss were found drawn out and contorted 

 with it into acute folds and the whole mass intruded by later granite. 

 This shows that granite was intruded into schist. Some time later peg- 

 matite intruded the mass, probably as an end action of that particular 

 granitic intrusion. After the mass had cooled it was subjected to great 

 stresses to which it yielded with the formation of acute folds. That 

 the mass had cooled is shown by the sharp boundaries of the broken 

 fragments of the pegmatite dike as it was sheared diagonally by the 

 regional forces. This sequence of events then represents, though pos- 

 sibly only in part, the importance of the interval between two granitic 

 intrusions, for another granite clearly cuts across the whole complex 

 mass. Nor is the case cited by any means rare ; on the contrary, 

 essentially the same thing may be found recorded in many boulders 

 scarcely two feet across on almost any of the alluvial fans along the 

 south front of the range. 



Great masses of granite have intruded the quartzites, schists, and 

 limestone north and northwest of Santa Ana Canon. Most of this 

 is of much the same general type, being a medium-grained muscovite- 

 biotite granite which is only rarely gneissic. Pegmatite dikes, while 

 hardly rare, are not at all conspicuous. South of Santa Ana Canon 

 and east of Rattlesnake Canon the granites are variable in character, 

 single areas of any one kind usually being only a few hundred yards 

 across. Pegmatite dikes are abundant and in some cases constitute 

 nearly half of the rock mass. The granites are usually gneissic and 

 often acutely interfolded with schists which they have penetrated. 

 As already stated, these are frequently cut by later granites. 



In lower Arrastre Creek the Arrastre quartzites and Furnace lime- 

 stone are intruded by a heterogeneous mass of granite ; but clearly 



