106 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
POST-PUENTE DIABASE. 
A dike of diabase nearly a mile long and varying in width up to an 
eighth of a mile breaks through the Puente sandstone and shale along 
the southern slope of the hills north of the mouth of Brea Canyon. 
The exposed portions of the rock are so much weathered that good 
specimens could not be obtained. The altered material is grayish in 
color and shows the light-colored, lath-shaped feldspar crystals very 
distinctly in the specimens examined. The outcrop of this rock in the 
face of the ridge north of the road connecting the Puente and Brea 
Canyon fields has the peculiar irregular contour which enables one to 
distinguish it at a glance from the adjacent sedimentaries. Farther 
east the weathering of the diabase has stained the soil a peculiar red¬ 
dish-brown color characteristic of the diabase areas throughout the 
Coast Range. The age of this diabase is approximately the same as 
that of similar diabase found in the Santa Monica Mountains in a like 
stratigraphic position—that is, it is post-Puente and pre-Fernando 
and belongs in the upper Miocene of the time scale. 
FERNANDO FORMATION. 
The youngest of the Tertiary formations in the Puente Hills is a 
succession of gray to yellow quartzose and granitic conglomerate and 
sandstone, together with interbedded arenaceous shale and clay, in all 
at least 1,500 or 2,000 feet. Occasionally a trace of eruptive debris, 
derived perhaps from the ranges to the north, is found with the other 
constituents, and locally a concretionary tendency may be observed. 
At one or two points, also—notably on the crest of Brea Ridge south 
of the Union Oil Company’s wells and on the main ridge north of the 
wells of this company in La Habra Canyon—the formation appears to 
carry a few inclusions of siliceous shale and calcareous concretions. 
The conglomerate, sandstone, and clay are fossiliferous, the forms indi¬ 
cating an identity of the beds with the Fernando of the Santa Clara 
Valley district. A feature characteristic of this formation is the 
ready disintegration of its sandy shale, which under heavy traffic 
becomes an extremely annoying dust. This formation flanks the 
Puente Hills on the north, south, and west sides. It also covers a 
large area in the Coyote Hills, 3 miles south of La Habra Canyon, and 
here some exposures of its sandstone show a deep rusty or crimson 
color. 
The following fossils, some of which are characteristic of this hori¬ 
zon, have been found in the Fernando beds, mostly in the vicinity of 
Olinda and Brea Canyon (see PI. XXXTY to XLI): 
