158 University of California Publications in Geology [Vol. 9 



Table Representing Number of Species from Cretaceous of Santa Ana 

 Mountains known also in Horsetown and Chico 



Horsetown Chico Creek 



Number of species of Pelecypoda 4 19 



Number of species of Gastropoda 5 



Number of species of Cephalopoda % 1 



Total number of species in common 4 25 



Per cent of species in common 5 31 



The small percentage of typical Chico species represented in the 

 southern fauna is clue in part to the fact that the fauna from the 

 Actaeonella oviformis zone is undoubtedly older than any horizon thus 

 far reported from Chico Creek. This lowermost fauna is more closely 

 related to the fauna from the beds immediately overlying the Horse- 

 town group in Shasta and Tehama counties than to the type Chico. If 

 the term Chico is made to include the known Cretaceous faunas of 

 California that are younger than the Horsetown fauna as previously 

 defined in this paper, the fauna from the Santa Ana Mountains may 

 be properly designated as Chico. Such a procedure does not conflict 

 with the generally accepted, though rather vague definition of the 

 Chico. It thus appears that the type Chico in the restricted sense 

 represents, as was pointed out by Anderson, but a portion of the Upper 

 Cretaceous column of California. 



Summary 



The Cretaceous strata of the Santa Ana Mountains are divisible 

 into at least two groups. The lowermost one, consisting of about 

 two hundred feet of red, non-fossiliferous conglomerates and sand- 

 stones, is here designated as the Trabueo formation. Conformably 

 overlying these beds is a series of conglomerates, sandstones, and 

 shales aggregating about two thousand feet in thickness, which have 

 yielded a rich invertebrate fauna. 



The Cretaceous fauna from the Santa Ana Mountains has certain 

 affinities with that of the uppermost Horsetown beds but is much more 

 closely related to the fauna from the Chico of Chico Creek. The small 

 per cent of typical Chico species represented in the southern fauna 

 is due in part to the fact that the fauna from the lowermost beds of 

 the Santa Ana Mountains is undoubtedly older than any fauna thus 

 far reported from Chico Creek, and also due in part to environmental 

 differences resulting from the distribution of land on this Coast during 

 the Upper Cretaceous. 



