162 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
the oil zone are similar to those found in the same position in the 
central and western fields and consist largely of soft, thin-bedded 
sandstone and sandy shale, dipping approximately S. 10° W. 
GEOLOGY OF THE WELLS. 
The underground geology of the eastern field is similar to that of 
the central, and is what would be expected from an examination 
of the surface evidence in the region. Within the productive territory 
the wells first penetrate the sandy shale of the Fernando, after which 
they enter the Puente clayey shale and “shell” beds which mark the 
top of the productive zone. Oil occurs in two sands, the upper being 
about 55 feet and the lower about 25 feet thick. At the present time 
the upper sand is practically exhausted, having been pumped con¬ 
tinuously for nearly seven years. Ten or twelve barrels per day was 
not an unusual yield when the sand was first struck, and even three 
years ago some of the wells were still yielding 1 or 2 barrels. The 
gravity of the oil in the upper sand is said to be between 18° and 19° 
B. The lower sand is medium to coarse grained and at first yielded 
as high as 25 barrels in some of the wells, but, like the upper sand, 
soon fell off and is now practically exhausted. The gravity of the 
oil in this stratum is about 16° B. Considerable quantities of gas 
accompanied the oil in the lower sand. Water occurs at a depth of 
about 900 feet in the neighborhood of Yale and Bernardo streets and 
in the extreme west end of the field was so abundant as to stop devel¬ 
opment work in the region south of the Sisters’ Hospital. 
The two following logs illustrate the strata penetrated in the areas 
of low and steep dip, respectively, in the productive territory of the 
eastern field: 
Typical ivell log in the central portion (strata of low dip) of the eastern field , Los Angeles. a 
Thick¬ 
ness. 
Depth. 
Sandy shale. 
Feet. 
325 
Feet. 
325 
380 
383 
395 
450 
453 
483 
485 
510 
512 
552 
Clayey shale, bituminous. 
55 
Hard shale. 
3 
Clayey shale. 
12 
Oilsand (oil 18.75° B.). 
55 
Hard shale. 
3 
Tough clay shale. 
30 
Hard shale . 
2 
Oil sand (oil 16° B.). 
25 
Hard shale. 
2 
Tough clay shale. 
40 
aHershey, O. H.. Bull. California State Mining Bureau, No. 19, 1900. p. 45. 
Typical well log in the eastern portion {strata of steep dip) of the eastern field, Los Angeles. 
1 
Thi ck- 
ness. 
Depth. 
Sandy shale with clayey shale toward hase. 
Feet. 
700 
Feet. 
700 
900 
1,060 
1,160 
1,204 
Oil sand (nearly exhausted when penetrated in 1902). 
200 
Clayey shale.... 
160 
Medium to coarse oil sand (25 barrels oil and considerable gas). 
100 
Clayey shale. 
44 
