LOS ANGELES DISTRICT: PUENTE FORMATION. 149 
at least 400 to 500 ieet of very dark colored, highly carbonceous, 
thinly laminated gypsiferous shale, showing traces of sulphur on the 
weathered surfaces. Associated with this is dark-brown sandy shale, 
interstratified with yellowish limy layers containing gray to yellowish 
calcareous elliptical concretions as much as 5 feet in length. Thin- 
bedded white chalky shale containing numerous fish remains is also 
found a little to the southwest of Sycamore Park. In the region 
about the mouth of Cahuenga Pass, where the shale is intruded by 
diabase, it is much contorted and fractured, gray to discolored blue 
gray and rusty brown in color, in places gypsiferous, and much of it 
tending to concretionary structure. 
The upper 1,000 feet or more of the upper Puente shale consists 
principally of soft, thin-bedded clayey to sandy shale, varying in 
color from gray through light yellow to rusty brown and locally, 
where oil bearing, to bright tints of yellow and pink. A peculiar 
efflorescence characterizes the weathering of the sandy members of 
these upper beds in many places. At the top of the formation are 
two bands of thinly laminated, alternating hard white and soft drab 
shale, separated by about 125 feet of coarse sandstone, the latter 
being shown on the map (PI. XVIII) by a special legend. These two 
shale bands, with their interbedded and underlying thin-bedded 
sandstone, mark the principal oil-bearing zone in the Los Angeles 
district. 
Associated with the shale at the top of the lower half of the upper 
Puente shale is a 50-foot band of coarse arkose sandstone, which is 
shown on the map in the same color as the Puente sandstone. 
OIL SANDS. 
As mentioned in the preceding section, the productive oil sands 
occur interbedded with the shale near the top of the Puente forma¬ 
tion. Exposures of these sands are to be found almost continuously 
along the mapped oil-sand zone, running from the Sisters’ Hospital, 
on Sunset boulevard, to the bend in the Hollywood and Cahuenga 
Valley Railroad, on Western avenue. The surface exposures of the 
upper sands, which aggregate about 125 to 150 feet in thickness, usu¬ 
ally either are more or less impregnated with oil or asphaltum or else by 
their color show the effects of its former presence in the beds. These 
sands vary in color from brown to dark drab and in some instances 
show bright tints of pink, purple, and yellow. As a rule they are 
coarse and in places, notably toward the west end of the district, 
they are more or less finely conglomeratic. The concretionary tend¬ 
ency is also characteristically shown in certain of the beds. In the 
low hilly region flanking the Elysian Park hills on the west what is 
supposed to be the equivalent of a part of the oil sands is character¬ 
ized by large, hard concretions. (See PI. XXI, A.) At one place 
Bull. 309—07-11 
