Geol.— Vol. II.] ANDERSON— STRATIGRAPHIC STUDY 1 79 



which a characteristic blue or bluish gray color predomi- 

 nates, at least in certain localities. In the vicinity of the 

 Etchegoin ranch, some twenty miles northeast of Coalinga, 

 these blue sands are distributed in three prominent horizons 

 including about twelve hundred feet of strata. They can be 

 traced with more or less continuity throughout the field from 

 the Cantua southward to the Sunflower V'alley. 



The blue color has been generally found to be a safe 

 index to the identit}^ of the beds and has been recognized in 

 the vicinity of Mount Diablo and on San Pablo Bay. It is 

 not claimed, however, that it is constant or characterizes any 

 particular strata within this division. In thickness the 

 Etchegoin Sands vary considerably. Near the Cantua 

 the thickness appears to be less than on the Etchegoin 

 ranch, while south of Alcalde the thickness is considerably 

 greater. 



In the vicinity of Kreyenhagen's where the Etchegoin has 

 its greatest development, the strata included within the limits 

 of the blue sands are twenty-five hundred feet, of which 

 ordinary gray sand and gravels form the larger portion. Many 

 of the pebbles are jet black in color. 



The Etchegoin Sands are commonly coarse in texture and 

 often pebbly, forming beds of conglomerate. There is an 

 appearance of volcanic ash or Kaolin-like matter throughout 

 the colored zones, and their characteristic color may be 

 partly due to this material, but the exact nature of the color- 

 ing matter has not been determined. 



One or two fossil horizons are to be recognized in the 

 Etchegoin Sands, one near their bottom and another some 

 distance above, but whether persistent or not cannot be 

 stated. The more characteristic horizon is that near the 

 bottom of this division and includes the following species: 



Pseudocardiurn gabbi Remond Scute lla sp. 



Area trilitieata Conrad Mytilus (large sp. ) 



My a arenaria Linn. Ostrea attwoodi Gabb 



Pectunculus sepientrionalis Midd. Cardium meekiatimn Gabb 



The second fossil horizon occurs higher up in the beds, 

 nearer their top, and contains the following: 



