1914] 



Dicker son: Martinez of Bock Creek 



293 



MAETINEZ GBOUP 



The Martinez is found in an area about six miles long and two 

 miles wide near Shoemaker. The group is apparently separable into 

 at least two terranes, a lower, predominantly sandstone, and an upper, 

 predominantly shale member. Unfortunately, as the mapping shows, 

 the two members were found only in fault contact ; hence their 

 relations to each other are not entirely clear. The basal member of 

 the lower terrane rests upon a granite block, which has been uplifted 

 along the San Andreas fault. This contact is well exposed on the 

 north side of a spur of Pinyon Ridge one-half mile south of Shoe- 

 maker. The line between the Martinez and the granite is very uneven. 

 The granite basement shows irregularities whose differences must have 

 been from thirty to fifty feet at the time the Martinez conglomerate 

 was deposited upon it. The conglomerate is not very thick and is 

 interstratified with a red shale in which large, highly polished granite 

 boulders are found. This shale contains some gypsum and in places 

 gypsum has penetrated into the irregularities of the granite basement. 

 A stratum of hard, gray, quartzose sandstone and several beds of 

 limestone were found interstratified with the red shale member, which 

 was about three hundred feet thick. Most of the fossils were found 

 in limestone lenses in the shale. These beds have a dip of 30° W and 

 strike of N 25° W. Above them appear about one hundred and fifty 

 feet of medium-grained, arkosic sandstone with subordinate strata of 

 limestone. Resting upon this at the top of Pinyon Ridge are one 

 hundred and fifty feet of shale weathered to a red-brown which have 

 been called the "coffee-ground" beds owing to their habit of breaking 

 into angular fragments of small size. Lack of good exposures pre- 

 vented further observations along the west end of Pinyon Ridge, but at 

 least several hundred feet are present. Along Rock Creek about one 

 mile south of Shoemaker is another partial section which is much 

 higher in the series. It is in ascending order as follows : 



Shale and limestone (lower beds) 100 ft. 



Tan sandstone grading into well cemented conglomerate .' 50 



Limestone and shale 150 



Yellowish sandstone, with a stratum of carbonaceous shale or impure 



lignite one foot in thickness ' 75 



Carbonaceous shale, lignite strata one foot in thickness alternate with 



gray sandstone and conglomerate strata 25 to 30 ft. thick 150 



Massive gray sandstone with conglomerate 150 



