174 



University of California. 



[Vol. 3. 



OCCURRENCE. 



The rock which forms the subject of these notes is exposed 

 at the quarry of the Granite Rock Company on the Pajaro River, 

 about seven miles east of Pajaro station on the line of the 

 Southern Pacific Railroad. It forms the axis of a ridge running 

 approximately N. 35° W., through which the river has cut a 

 gorge Ave hundred feet deep, the walls on both sides being 

 composed largely of the rock under discussion. Southward 

 along the ridge the rock can be traced on the east flank, by 

 exposures in the gullies, for a mile; further south the overlying 

 sedimentaries cover it completely. To the north of the river 

 canon no good outcrops have been found, the only indications 

 consisting of surface wash, which contains fragments of the rock, 

 on the west flank of the ridge. In the canon the north wall, while 

 presenting a few jutting outcrops, is too overgrown with heavy 

 brush or covered with soil to allow much investigation. It is 

 only on the south, where the quarry faces are being worked, that 

 the rock can be well seen. 



GEOLOGICAL RELATIONS. 



The ridge of which this rock forms the axis is one of a series 

 of parallel ridges composing this portion of the Coast Ranges. 

 From the Pajaro River at the quarry, for three miles south the 

 altitude of the hills is comparatively low, midway between the 

 Santa Cruz Mountains on the north and the Gavilan Range on 

 the south. For lack of a better arbitrary line dividing these two 

 units of the California Coast Ranges, and because the igneous 

 rock to be discussed is probably genetically connected with the 

 granite of the Gavilan Mountains, the Pajaro River will be taken 

 as dividing line, and all south as a portion of the Gavilan Range. 



At the point of best exposure of the rock, the San Juan 

 valley lies to the southeast, and the upper Pajaro valley to the 

 west. The Pajaro River approaches from the southeast and flows 

 for half a mile along the line of contact between the plu tonic 

 rock and the overlying sedimentaries. It turns then nearly at 

 right angles directly across the ridge, and flows south west ward 

 toward the ocean. A very sharp elbow is thus formed. 



The ridge has the nature of a simple fold, with the plutonie 



