1916] 



Packard: Cretaceous of Santa Ana Mountains 



141 



the Chico conglomerates are conformable upon those of the Trabuco 

 appears to be indicated at one locality where a gradation from a red 

 to a gray conglomerate was noted. 



These red Trabuco conglomerates are composed of both angular 

 and water-worn boulders varying in size up to those having a diameter 

 of three feet. The boulders represent a considerable range of rock 

 types, the majority of the igneous rocks being- basic. In places subord- 

 inate bands of red sandstone occur interbedded with the conglomerates. 



The peculiar color, the angular form of most of the pebbles and sand 

 grains, and the lack of marine fossils suggests that the Trabuco forma- 

 tion was deposited upon a narrow coastal plain, by torrential streams 

 arising in a mountainous region but a short distance to the eastward. 

 After about two hundred feet of this material had been laid down, 

 marine conglomerates of the basal Chico accumulated within the waters 

 of the transgressing sea. 



The age of the Trabuco horizon is not definitely known, since as 

 yet it has yielded no fossils. Judging from its stratigraphic relations 

 the formation is probably but slightly older than the Chico group and 

 presumably represents some phase of the pre-Chico Cretaceous. 



THE CHICO GEOUP 



Resting with apparent conformity upon the Trabuco formation is 

 a series of conglomerates differing from those of the lower formation, 

 in the lighter color of the matrix, in the firmer cementation, in the 

 greater abundance of pebbles of quartzites and slates, and in the 

 inclusion of marine fossils in the matrix and in the rounded boulders. 

 The fossils from the boulders comprise fragments of Inoceramus and of 

 an indeterminate gastropod, suggesting the occurrence of earlier 

 Cretaceous deposits now completely removed by erosion. 



The conglomerate resting upon the Trabuco grades upward into 

 coarse, light-colored sandstones with subordinate strata of hard, fine- 

 grained calcareous sandstone bearing a characteristic fauna. Follow- 

 ing these are several hundred feet of laminated, bluish shales, often 

 containing limestone nodules. The nodules are occasionally fossilifer- 

 ous. Above the shales the strata again become coarser, being composed 

 of sandstones, which in places grade laterally into conglomeratic lenses. 

 These beds are succeeded by a series of alternating strata of sandstone 

 and shale, which in turn are replaced in the upper portion of the 

 section by hard, fine-grained, calcareous sandstones, fine tan-colored 



