286 GUIDEBOOK OF THE WESTERN UNITED STATES 
Streets above the tunnel are exposures of these shales overlain by 
dark, massive sandy shale of Pliocene age. Good sections of the 
Topanga formation (middle Miocene) appear on Glendale Boulevard 
between the Los Angeles River and Los Angeles, where the formation 
is 2,000 feet or more thick and the beds dip to the south. A con- 
spicuous Miocene sandstone is exposed in Elysian Park. The general 
structure about Los Angeles is that of a syncline or basin bordered in 
part on the north and east by faults. 
At Elysian Park, along the west side of the Los Angeles River, the 
railroad cuts expose sandstones of middle Miocene age overlain by 
upper Miocene shales. These beds are on the south limb of an 
extensive anticline whose axis lies in the bed of the river farther north. 
On Fifth Street, opposite the Public Library, upper Pliocene fossilifer- 
ous beds are well exposed. The strata east of the river consist 
mainly of highly folded middle and upper Miocene beds. (Kew.) 
The hills in northern Los Angeles and western Alhambra consist of 
a thick succession of Miocene, Pliocene, and Pleistocene strata com- 
prising conglomerate, sandstone, siltstone, and shale. In the upper 
Miocene are many beds of siliceous and diatomaceous shale. The 
total thickness of these strata is apparently 11,000 feet. They lie 
on the older granites and metamorphic rocks. The Miocene rocks 
are exposed in many street cuts east of Lincoln Park adjacent to 
Valley Boulevard. Upper Miocene (Puente) shale and interbedded 
sandstones are exposed near City Terrace. (R. D. Reed.) 
In the central part of Los Angeles is a belt of petroleum-producing 
territory 5% miles long, covering an area of 2 square miles. Here 
hundreds of derricks have been erected in close proximity to dwellings. 
This field was discovered in 1892 by a 155-foot shaft sunk near a 
small deposit of brea or asphalt on Colton Street. The first good 
strike of petroleum was made in a well on Second Street, and by the 
end of 1894 there were 300 producing wells from 500 to 1,200 feet 
deep. The wells have been small producers, averaging 2% barrels a 
day each by pumping, and now much of the area is drained of its oil. 
The Salt Lake field is also within the city limits, about 4% miles west 
of the business center. It was started in 1901 and has been a notable 
producer, having 700 wells in 1914. The wells are mostly from 1,200 
to 3,000 feet deep, and in most of the area there has been considerable 
gas, which caused the wells to gush in the early part of their life. 
The average production per well was 23 barrels a day, and the total 
_ production from 1894 to the end of 1931 was over 60,000,000 barrels. 
_ (Hoots.) The oil has been mainly useful for fuel. The petroleum 
in the Los Angeles district is derived largely from the upper 500 feet 
3 of the Miocene and the basal beds of the Pliocene. The oil pools — 
are thought to be related to slight arching along the younger dis- 
