186 
OTL DISTRICTS OF SOUTHERN CALIFORNIA. 
flexure trending northeast and southwest probably changes the gen¬ 
eral dip of the beds from southwest in the region of the Colegrove 
group of wells to west and then to northwest toward the center of the 
Salt Lake held. 
The contour lines on the map (PI. XIX) give an approximation of 
the depth of the top of the upper oil sand or zone below Los Angeles 
city datum (255 feet above sea level). 
SALT LAKE FIELD. 
LOCATION. 
The Salt Lake field—so named from its first important producing 
company—occupies an area approximately a mile square near the 
intersection of Fourth street and La Brea road, 7 miles west of the 
business portion of Los Angeles. The productive territory as now 
developed embraces the northwestern part of the SE. J, the north¬ 
eastern part of the SW. 1, and the southern part of the N. \ sec. 21, 
T. 1 S., R. 14 W. In addition to this there are some important wells 
in the central part of the E. | sec. 20 and some small producers in the 
NW. 1 sec. 28. 
The field occupies a part of the Los Angeles-Santa Monica plain, 
which extends southward with a gradually lessening slope from the 
base of the Santa Monica Mountains toward the hills southwest of 
Los Angeles. (See PI. XXIII.) 
GEOLOGY. 
GENERAL STATEMENT. 
Alluvium and Pleistocene deposits of gravel, sand, and clay cover 
the plain in the region of the Salt Lake field, but surface outcrops of 
other beds are to be found no nearer than about 2 miles from the 
present developed territory. The well logs and a study of the adja¬ 
cent territory indicate, however, that the formations involved in the 
geology of this field include at least a part of those exposed to the 
east in the vicinity of the Los Angeles city field. They are (a) 2,000 + 
feet of Puente sandstone; ( b ) 2,0004= feet of upper Puente shale and 
thin-bedded sandstone; (c) 2,000+ feet of Fernando clayey and 
sandy shale, sandstone, and gravel, and ( d ) an unconformable capping 
of Pleistocene gravel, sand, and clay varying in thickness from 40 to 
190 feet or more, the whole covered by alluvium. A detailed descrip¬ 
tion of these formations is given in the discussion of the general 
geology of the district and will not be repeated here. 
OIL SANDS. 
The most productive sands occur at the top of the Puente forma¬ 
tion although traces and locally more or less important accumulations 
of oil and gas are found in the shale above the principal oil zone. 
