Vol. 5] 



Weaver. — San Pablo Formation. 



255 



side of the valley the San Pablo again outcrops on the two sides 

 of an anticlinal axis. The axis of the anticline extends along 

 the ridge between Bolinger Canon and San Ramon Valley. 

 The core is composed of Monterey and the axis pitches in a south- 

 easterly direction, so that the San Pablo of the eastern flank 

 swings around and covers the Monterey on the south side of the 

 ridge and then passes southwesterly and outcrops in the hills on 

 both sides of Bolinger Canon forming the western flank of the 

 anticline. Here again the Monterey and San Pablo can not be 

 separated on a lithological basis but only by means of fossils. 

 The thickness of the San Pablo measured across the strike just 

 below the town of Danville is about seven hundred feet. Near 

 the base it is made up of heavy, thick-bedded, coarse, gray, and 

 sometimes conglomeratic sandstones with occasional small bands 

 of shale or conglomerate. Farther up in the series conglomer- 

 ates become more abundant and near the uppermost part of the 

 strata which are exposed there is an abundance of shale. The 

 uppermost beds are covered unconformably by the alluvium of 

 the valley. No white chalky shales were seen at the base nor 

 tuffs at the top. On the eastern limb of the anticline the strata 

 dip at an average angle of about 50 degrees to the southeast. 



In San Eamon Valley, extending southwest from the town 

 of Walnut Creek, San Pablo strata are again well exposed. Well 

 marked outcrops occur in the creek bed at Walnut Creek and in 

 the low hills along the east side of the creek and Southern Pacific 

 railway track. About two miles south of the town of Walnut 

 Creek a detailed section was measured across the strike of these 

 beds. The section extends through the highest point on Sugar 

 Loaf Mountain, then across the valley and into the hills on the 

 west side of the railroad track. The strata dip at an angle of 

 about 55 degrees east. These beds lie upon the Monterey, but 

 the line of contact is not certain as there are no well defined out- 

 crops. The strata have the same general appearance but at 

 points to the south the contact has been determined upon a pa- 

 laeontologieal basis. No white chalky shales were seen. The 

 most prominent outcrop near the base is in the Southern Pacific 

 railway cut on the west side of the county road just before it 

 crosses the town of Walnut Creek. Coarse, thick-bedded, gray 



