320 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
south of east from Los Angeles. The altitude of their highest point 
is 1,655 feet above sea level. Their slopes are comparatively smooth 
and well grassed, and in certain localities there are limited areas of 
oaks. Tributaries of the San Gabriel drain them on the north, and 
of the Santa Ana on the south, but for most of the year the stream 
courses are dry. 
The formations embrace sandstones, shales, and conglomerates, 
which from present evidence are to be regarded as equivalents of the 
Lower Miocene, Monterey, and San Pablo formations. The Lower 
Miocene is represented by several hundred feet of yellow and gray 
concretionary sandstones, with thin, interbedded layers of siliceous 
shales of Monterey type. These sandstones have an enormous devel- 
opment in the eastern half of the Puente Hills, and according to 
report continue southeastward across the Santa Ana River into the 
Santa Ana Range, where fossils have been found in them which 
determined their horizon. 
The interbedded shales of this series, while of the Monterey type, 
arc hardly to be classed in this division of the Miocene, by reason of 
their occurrence in the midst of sandstones which are known to carry 
Lower Miocene fossils. On the other hand, in the western half of the 
hills there are strongly developed siliceous shales that carry Monterey 
fossils and are to be regarded of this age. 
The third and youngest series of rocks in the Puente Hills, forming 
a prominent terrane along their southern base, is referred, from its 
fossils and its lithologic features, to the horizon of the San Pablo. 
The formation here consists of several heavy conglomerates, sand- 
stones, and argillaceous shales and clays. The sandstones and clays 
break down and disintegrate to the same impalpable powder as do 
those of the formation in the region of Sunset, McKittrick, and Coal- 
inga. This formation rests unconformably upon those below. 
The structure of the Puente Hills is that of an anticline modified 
by numerous subordinate flexures, the axes having a general trend 
of N. 65° W. The western half is greatly contracted in its width, 
while the eastern half is correspondingly expanded. Faults, also, 
have entered to an important degree into the structure of the hills, 
especially along the southern slope. Of these, or of an excessively 
sharp crumple accompanied by minor anticlinal flexures, an especial 
instance is to be found in a line of disturbance that passes immedi- 
ately north of the Santa Fe wells, crosses to Brea Canyon, and is, in 
fact, traceable at intervals over the entire distance to the region of 
the Whittier wells. The Santa Fe and Brea Canyon wells are close 
to this line of disturbance ; perhaps, also, the wells east of Whittier. 
The Puente wells, lying between the latter and those of Brea Canyon, 
are situated at some distance from the fractured zone, yet are to be 
found in an area of considerable crumpling immediately adjacent to 
the axis of the main fold. The geology in the immediate vicinity of 
