Vol. IV] ANDERSON AND MARTIN— NEOCENE RECORD 49 



rocks are exposed only where stream erosion has removed the 

 mantle of gravels. These deposits were eroded from the higher 

 portions of the San Jose Range by the agency of streams and 

 laid down again upon the surface of the Miocene. 



An unusual development of these gravels can be seen in the 

 north-central part of T. 29 S., R. 16 E., and in the southern 

 part of T. 28 S., R. 16 E., between Navajoa Creek and Cam- 

 mattii Canyon. In viewing this region from a distance it 

 appears as a nearly level tableland standing out in sharp 

 contrast to the adjacent hills. Closer observation discloses 

 numerous wide ravines cutting deeply into the apparently flat 

 surface. The areas between these ravines are flat, producing 

 the tableland appearance. The rock exposed in the beds of 

 the ravines is gravel, indicating that the Miocene beds have 

 been covered by them to the depth of the ravines themselves, 

 which in some cases is more than 250 feet. In no locality be- 

 tween the Navajoa Creek and Cammattii Canyon do the 

 Miocene beds outcrop. In the hills east of Navajoa Creek and 

 also west of Cammattii Canyon, rocks of the Miocene group 

 are exposed at elevations far above the beds of the ravines 

 described above. The explanation of this peculiar condition 

 is that the Navajoa Creek has in former time swung back and 

 forth between Cammattii Canyon and its present position, re- 

 moving all of the Miocene rocks to the depth at least of the 

 present beds of the ravines. This removal of the Miocene rocks 

 from the area probably took place during an epoch of uplift. 

 When the region subsequently sank the flood plain of the 

 Navajoa was aggraded and filled by stream gravels or alluvium 

 at least to its present thickness. Whether these gravels repre- 

 sent remnants of the Paso Robles formation, or not, is a de- 

 batable question. In many localities they are associated with 

 sands and clays which are also a part of the Paso Robles forma- 

 tion. In the southern part of the district there is a large 

 area of gravels which is apparently due entirely to stream 

 action. The gravels are distributed over the Miocene sedi- 

 ments almost as far back as the edge of the granite area of 

 the San Jose Range. Along the northern and eastern parts of 

 the San Juan district the Miocene is entirely covered by these 

 gravels, which are in part Paso Robles. 



