ARNOLD — THE PALEONTOLOGY AND STRATIGRAPHY OF SAN PEDRO 57 



Sail Junn Cnpidrano.—The following fossils were taken from a sliallow well at Ban 

 Juan C'ajiistrano, in which were also found a tusk and some of the bones of a raastodon:' 



Area (cf.) sitlicosln A^aiica ciaiisa 'I'urrll'lla coopuri 



Crepidula excavata Osirea (?) Vcnericardiaborealis[=V. vinlriro^a} 



Nassa mtndka Leda ( ?) Vola ( ?) 



Dr. Merriam is of the opinion that these fossils are of Pliocene age — an opin- 

 ion borne out by the similarity of this fauna to that of the Deadman Island Pliocene. 



At Bell Station, on the Los Angeles Terminal Railway in Los Angeles County, 

 the following fossils were obtained from a well at a depth of between 920 

 and 1,320 feet.' 



Amiantja callosa Mijui-fUa (aff.) .i/m/i/rx [= Terr- OliocUa ba:tica [=0. pedroaua] 



Echinarachniax cxcenlricus bra id.] li(t:ta undulala 



Macoma na.futa LiinaUa Icirisil Tornalella (?) 



This is an upper San Pedro fauna, and its occurrence at such a great depth 



has much significance in showing the great amount of sedimentation that has taken 



place in the region between Los Angeles and the ocean since the deposition of the 



San Pedro series. 



San Diego and Vicinity.^ 



The Pliocene and Pleistocene deposits of San Diego are similar to those of San 

 Pedro, and the geologic history of the two regions has been nearly the same. 

 During the Pliocene epoch the region now occupied by San Diego Bay and vicinity 

 was a great basin in which coarse gravels and fine sands were deposited. The earlier 

 sediments, which are now exposed along the northern portion of the San Diego mesa, 

 consist of thick deposits of incoherent coarse gravels, while the later deposits are 

 made up of plainly bedded yellow sandstones. After the deposition of these layers, 

 there was an interruption of sedimentation, which was followed during Pleistocene 

 times by an inundation and deposition of fossiliferous gravels and sands over nuich of 

 the San Diego region. 



Pacific Beach — Pliocene. — The best exposure of the Pliocene is found at 

 Pacific Beach, on the coast ten miles north of San Diego. A perpendicular bluff, 

 varying in height from four feet at Ocean Front to over sixty feet one mile north, 

 forms the coast line of Pacific Beach. This bluff is composed of brownish yellow 

 sandstones of Pliocene age, which dip gently toward the south, and di.sappear succes- 

 sively beneath the beach as one approaches Ocean Front from the north. The total 

 thickness of the strata exposed is about two hundred feet. The upper one luindred 

 feet are fossiliferous, while the lower layers are devoid of fossils. The unfossiliferous 

 sandstone rests upon coarse incoherent gravels of uidviiown thickness. 



There appear to be two quite distinct horizons in the fossiliferous section of 

 the Pacific Beach Pliocene. Stratigraphically no distinction can be made, as the 

 whole series of strata rest conformably upon one another, but faunally there is 



I Op. ci(.. pp. 59 and 222. ^Op. cit.. p 223. 



3 The late Tertiary and Pleistocene formations in the vicinity of S.in Diego are mentioned in the following papers; 



Distribution of California Tertiary Fossils. By W. H, Dall. Proc. U. S. Nat. Museum, Vol. I. 1879. pp. 2li-:i0. 

 North .American Tertiary Horizons. By W. H. Dall. 18th .\nn. Rept. V. S. Geol. Snr.. Part II, 1898, p. 335. 

 , Geology of San Diego County; also of portions of Orange and San Bernardino Counties. By H. W. Fairbanks. Uth Ann. Rept. 

 Cal Stale Mineralogist, 1893, pp. 7(>-120. 

 ( 8 ) September 27, 1902. 



