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University of California Publications in Geology [Vol. ll 



COMPARISON WITH FAUNAS OF THE PACIFIC COAST PROVINCE 



In the sequence of late Tertiary faunas of the Pacific Coast 

 province the Ricarclo assemblage shows relationship to the faunas of 

 the Chanac formation at the lower end of the San Joaquin Valley, 

 the Lower Btchegoin or Jacalitos and the Middle Etchegoin of the 

 North Coalinga region, and the Pinole Tuff-Orinda fauna of the San 

 Francisco Bay region. 



The Chanac fauna includes hipparions, Merycodus, a rhinocerotid, 

 rare remains of Protohippus, and possibly Pliohippus. As yet no 

 horses have been found in the Chanac which seem to correspond 

 specifically to Ricardo forms, but the dominance of hipparions 

 approaching in characters one of the Ricardo species suggests similar 

 time stage of the two faunas. As rhinoceroses are unknown in the 

 Ricardo the presence of a member of this group in the Chanac may 

 mean considerable separation of these two faunas in time, or may 

 indicate difference in habitat. 



The presence of Hipparion in the lower Etchegoin and its failure 

 to appear in the Middle Etchegoin may be taken to indicate closer 

 approximation of the Ricardo to the lower division than to the middle 

 or Pliohippus coalingensis zone. In the character of the Pliohippus 

 species the P. coalingensis zone fauna is not widely removed from 

 that of Ricardo, but there seems in general reason for considering the 

 Middle Etchegoin as near the Rattlesnake-Thousand Creek stage of 

 the Great Basin province, and it is not improbable that a fuller 

 knowledge of the fauna may reveal types more advanced than those 

 of the Ricardo. 



The Pinole Tuff-Orinda fauna as known by the best representation 

 from San Pablo Bay comprises an assemblage of forms suggesting 

 the Thousand Creek, Rattlesnake, and Middle Etchegoin stages. It 

 appears to be somewhat later than the Ricardo. In beds considered 

 to represent a stage of the Orinda in the Contra Costa Hills Hipparion 

 remains have been obtained representing a form specifically not dis- 

 tinguishable from Hipparion mohavense of Ricardo. Another assumed 

 Orinda specimen, the type of Hipparion platystyle, closely approaches 

 one of the large Ricardo Hipparion forms with somewhat compressed 

 protocone. It is possible that the beds containing these Ricardo-like 

 forms of the Orinda are older than those on San Pablo Bay containing 

 Pliohippus species without associated Hipparimv. 



In general the Ricardo stage is not far from that of the Pinole 

 Tuff-Orinda, but may be somewhat earlier. 



