1916] 



Packard: Cretaceous of Santa Ana Mountains 



different horizons are not so easily distinguished." 7 Anderson chose 

 therefore the following localities outside of the Great Valley as typical 

 of the Lower Chico: 8 San Diego, California, Silverado Cafion, (Santa 

 Ana Mountains) Henley, California, and Phoenix, Oregon. He assigned 

 the type Chico of Chico Creek, Pence's Ranch, Texas Flat, and Tuscan 

 Springs to the Upper Chico. All of these localities are in the upper 

 portion of the Sacramento Valley. 



The Silverado Caiion fauna apparently includes only the lowermost 

 fauna from that region. The fauna listed from San Diego, obtained 

 from Point Loma and Point La Jolla, is comparable to the fauna from 

 the lower zone of the Santa Ana Mountains. The different faunas 

 which are considered as equivalent to the upper Chico include the 

 fauna from Chico Creek. It thus appears that Anderson recognized 

 that the Chico Creek fauna represented but a portion of the Upper 

 Cretaceous of California. 



A review of the geologic literature dealing especially with the 

 Santa Ana region has been amply covered in a recent paper by Dr. 

 Roy E. Dickerson entitled "The Martinez and Tejon Eocene and 

 Associated Formations of the Santa Ana Mountains." 9 



Geology op the Region 



GENERAL GEOLOGIC RELATIONS 



In the rocks of the Santa Ana Mountains the following geological 

 divisions are represented ; a basement complex of questionably Triassic 

 age ; Upper Cretaceous, Chico ; Lower Eocene, Martinez ; Upper Eocene, 

 Tejon ; the lowermost Miocene, Vaqueros ; and alluvium of probable 

 Pleistocene age. The intrusives and the metamorphosed sedimentaries 

 of the basement complex comprising the core of the range are un- 

 conformably overlain by the Cretaceous sandstones and conglomerates. 

 Both the Martinez and the Tejon are represented by small remnants, 

 which are shown by Dickerson 10 to be discordant with both the under- 

 lying Cretaceous and the overlying Miocene. The latter strata suc- 

 cessively overlap the Tejon, Martinez, and Chico, and at Arroyo 

 Trabuco are in contact with the basement complex. 



The Cretaceous occurs on both sides of the range. It outcrops on 

 the western flank of the mountains in a band having a maximum width 



i Op. cit., p. 25. 

 a Ibid., p. 26. 



» Univ. Calif. Publ. Bull. Dept. Geol., vol. 8, pp. 257-274.1, pis. 26-28, 1914. 

 i» Op. cit., pp. 263-267. 



