190 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
thickness and composition in the different wells. This is to be 
expected, since individual layers in surface outcrops of similar beds in 
the Los Angeles region undergo important changes of thickness and 
grain within remarkably short distances. The upper oil sand on the 
northwest side of the flexure appears to become less and less impreg¬ 
nated with petroleum as it approaches the apex of the flexure. This 
condition is probably due to structural causes, such as the loss of the 
oil through fractures, although it may possibly be accounted for by a 
slight change in the grain of the sand near the flexure. The same 
beds, however, continue to carry considerable quantities of gas as 
they pass over the line of the disturbance. 
The “main sand/’ which yields the bulk of the oil, is apparently 
fairly constant over a large part of the field. This sand is approxi¬ 
mately 100 to 125 feet thick, rather coarse-grained, and liighty 
impregnated not only with oil but with gas also. The tapping of the 
main sand usually results in the production of a “gusher,” owing to 
the great pressure under which the gas is confined. The retention of 
the oil and gas in this sand is due to the presence of an overlying 
bed of impervious “shell,” capped by 50 feet or more of hard clayey 
shale. The gravity of the oil in the same stratum is said to be differ¬ 
ent at different points down the dip. An illustration of this is found 
in a series of four wells running across the strike of the oil sand in the 
northern part of the field. The well highest up on the dip yields 14° 
oil; the next lower down, about 150 feet from the first, 15°; the third, 
150 feet from the second, 16°; and the fourth, or lowest of the series, 
100 feet from the third, 17°. , 
The two following well sections, one near the flexure, the other 
farther away and down the dip from it, are typical of the Salt Lake 
field: 
Typical well log near the flexure, on its northwestern flank, Salt Lake field. 
[Elevation about 225 feet; dip of strata approximately 40°.] 
Thick¬ 
ness. 
Depth. 
Clay. 
Feet. 
36 
Feet. 
36 
60 
Sand and gravel. 
24 
Heaving sand; first water cased off at 110 feet. 
30 
90 
Clayey shale. 
70 
160 
“Adobe” (sandy shale). 
90 
250 
“Adobe,” with salt water at base. 
12 
262 
Clayey shale; 2-foot “shell” at 275 feet. 
13 
275 
Clayey shale; no water. 
85 
360 
Clayey shale; 4-foot “shell” at 398 feet. 
38 
398 
Clayey shale. 
47 
445 
“Adobe” and clayey shale. 
41 
486 
505 
Sticky “adobe”. 
19 
Coarse gravel and “adobe”. 
21 
526 
“Adobe;” 4-foot “shell” at 632 feet. 
106 
632 
“Adobe;” last 10 feet very sticky. 
40 
672 
Clayey shale, 4-foot shell at 701 feet. 
29 
701 
“Adobe;” “shell” at 785 feet. 
94 
795 
Sticky “adobe;” second water shut off temporarilv. 
5 
800 
“Adobe;” considerable water.*.. 
118 
918 
