LOS ANGELES DISTRICT: CENTRAL FIELD. 167 
the bee Is is particularly noticeable along Ocean View avenue west of 
Alvarado street. Toward the east end of the field the sandstone is 
usually light to dark yellowish brown. Above the soft sandstone and 
sandy shale is a zone of fine-grained shale, several hundred feet in 
thickness. Some of this shale is hard and appears to be more or less 
calcareous. Veins of gypsum are abundant in this part of the forma¬ 
tion. Excellent exposures of this fine-grained shale are found on 
Beaudry avenue near Fourth street and in many road cuts both 
northeast and west of this locality. 
The uppermost beds of the Fernando exposed in Los Angeles lie 
south of the central field, occupying the ridge on which the State Nor¬ 
mal School is located. These are soft clayey shales and heavy-bedded, 
fine, light-colored sandstone with some interstratified conglomerates. 
The fossils listed on page 153 came from these beds in the region south 
of the central field. 
GEOLOGY OF THE WELLS. 
As indicated by the well logs, the underground geology varies some¬ 
what throughout the extent of the central field. The southerly dip 
of all the beds, however, is common from one extremity of the field to 
the other. The strata in general are less disturbed and dip at lower 
angles in the east end of the field, and the oil sand on that account 
appears thinner in that region. In the territory east of Belmont ave¬ 
nue most of the wells penetrate sandy and clayey shale (Fernando) 
for the first 500 or 600 feet. Beneath this is the oil sand, consisting 
of 125 feet of thick layers of coarse arkose material interbedded with 
thin clayey shale. About 200 feet beneath this sand is the lower pro¬ 
ductive zone, which consists of 40 to 50 feet of medium to coarse sand 
in layers similar to those of the upper zone. The two oil-bearing beds 
are separated in the northern part of the field by about 200 feet of 
tough blue clay, but toward the south this thins out and the pro¬ 
ductive sands tend to coalesce. On the south edge of the field the 
rocks below a depth of 950 feet consist of alternating clayey and coarse 
sandy layers, which replace the heavy, well-defined 10 to 15 foot sands 
farther north. The gas pressure is stronger and the oil more abund¬ 
ant, heavier, and redder along the south edge of the field than in the 
same beds nearer the surface in the northern portion. This reddish 
oil, it is said, gradually turns black on exposure to the air. Below 
the lower productive zone is 15 to 20 feet of clayey shale and thin- 
bedded sandstone carrying considerable quantities of water. The 
south edge of the field is defined by the line where this water becomes 
so abundant that it completely hinders development. The water level 
is said to be between 900 and 950 feet below the surface east of Bel¬ 
mont avenue and 1,050 feet west of it. 
