1917] 



Merriam : 



Pliocene Mammalian Faunas 



427 



to the Hipparion-bearing beds in the lowest portion of the Etchegoin 

 section. The Pinole Tuff-Orinda fauna seems certainly older than the 

 Pliohippus proversus zone of the Etchegoin. The fauna of the beds 

 furnishing the best collections of the Pinole Tuff and of the lowest 

 Orinda on San Pablo Bay is close to that of the Pliohippus coalin- 

 gensis zone of the Etchegoin. The Tulare evidently represents the 

 latest stage. 



The sequence of Pliocene faunas and formations of the Pacific 

 Coast province as we now know it is most satisfactorily expressed in 

 a series of four stages. All four of these faunas may be present in 

 one stratigraphic sequence in the North Coalinga region. 



The stages are as follows : 



Tulare fHyaenognathus zone 



Upper Etchegoin Pliohippus proversus zone 



Middle Etchegoin Pliohippus coalingensis zone 



Lower Etchegoin or Chanac ... Hipparion gratum tehonense or Hip- 



parion molle zone 



Great Basin Province 



In the Great Basin region there are four important occurrences 

 of Pliocene faunas. These are the Thousand Creek of the northern 

 Nevada or Middle Basin area, the Ricardo of the Mohave Desert, the 

 Rattlesnake of the John Day Valley, and the Idaho of southwestern 

 Idaho. 



The Rattlesnake fauna has unusual significance owing to excep- 

 tional clearness of stratigraphic relations of the beds in which it occurs. 

 The Rattlesnake formation rests in marked unconformity in steep cliff 

 section upon the Mascall, which contains a mammalian fauna of 

 Middle or Upper Miocene age. Through the accumulated Rattlesnake 

 deposits deep canons have been cut, and in the lower reaches of these 

 excavations are deposits containing a Pleistocene fauna. The age of 

 the Rattlesnake formation is therefore limited on one side by a period 

 of erosion and deformation succeeding accumulation of the Mascall 

 Miocene, and on the other side by a period of erosion preceding accum- 

 ulation of deposits of Pleistocene age. 



Within the past field season a party from the Department of 

 Palaeontology of the University of California has made intensive study 

 of the Rattlesnake formation and fauna, and has increased the list of 

 mammalian species considerably. 



