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University of California Publications in Geology [Vol.9 



Upper Miocene op Bear River 



At the mouth of Bear River, Miocene and possibly Pliocene 

 beds are to be found in the form of a synclinal fold. The sec- 

 tion along the beach across this syncline extends for a mile on 

 either side of the mouth of the river. On the north side of this 

 area the basal beds rest uneonformably upon a shaly portion of 

 the Mesozoic formation which forms the headlands at Cape Fort- 

 unas and Cape Mendocino. These beds extend southward to 

 within one mile of Cape Mendocino, where the basal portion is 

 again found in contact with the Mesozoic rocks. The strata at 

 this point dip northeast at an angle of thirty-five degrees. The 

 strike is N 60° W. On the north side of the syncline the strike 

 of the beds is N 50° W, and the dip is to the south at an angle of 

 seventy degrees. The middle or axis of the syncline lies about 

 half a mile south of the mouth of the river. The area covered 

 by this formation extends only a short distance up the stream, 

 and from a number of strikes and dips taken on either side of the 

 river it appears to be a crescent-shaped area representing the 

 extreme end of a syncline. In the lower portion the beds consist 

 of fine-grained sandstones and shales which have buff and brown- 

 ish-gray colors. Near the top of the section the strata consist of 

 gray sandstone with thin layers of clay interstratified with it. 



The determination of this formation as Miocene was made 

 upon the finding of Pecten peckhami Gabb, and sharks' teeth in a 

 small gulch a few hundred yards north of the mouth of Bear 

 River. A small collection of fossils made from the upper horizon 

 contained a number of species which are common to the Empire 

 Formation on Coos Bay. 



The following species were obtained from the upper portion 

 of the upper Miocene formation at the mouth of Bear River : 



Echinodermata Venericardia castor Dall 

 Schizaster stalderi Weaver Gasteropoda 



Pelecypoda Argobuccinum arnoldi Martin 



Chione, sp. Chrysodomus bairdi Dall 



Macoma calcarea Gmelin Liomesus sulculatus Dall 



Panope estrellana Conrad Tritonofusus saundersi Martin 



Phacoides acutilineata Conrad Turris cammani Dall 



Solemya ventricosa Conrad Volutopsius eurekaensis Martin 



All of these species, excepting those listed as new forms, occur 

 in the Empire Formation of the Oregon coast and it seems prob- 

 able that the two formations Avere approximately contempo- 

 raneous in deposition. 



