312 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
from it. A feature that is to be considered in this connection, how- 
ever, is the fact that because of the lenticular form assumed by the 
deposits of sands, gravel, and clays, a certain interlocking of sedi- 
ments has taken place that has permitted a free circulation of oil 
throughout the entire thickness of the oil-bearing zone, rendering it 
remarkably productive. 
The geologic structure of the entire region of which the Kern River 
field is a part has not yet been worked out. There is a general south- 
westerly dip of the Miocene beds from the Sierra granites outward, 
and there is abundant evidence also of subordinate folds, the axes of 
which lie more or less diagonal to that of the Sierra uplift. It is on 
the southwestern slope of one of the anticlines of this series that the 
oil field has been developed. The axial trend of this fold is approxi- 
mately N. 40° W., with Local variation to N. G0° or 70° W. With the 
rarest and most local exceptions, the dip is southwest, usually under 
5° and often but 2° or 3°; and in an examination of the Lower Mio- 
cene beds from the immediate vicinity of the granite outward there 
was found at no point a dip in excess of 10°. Along the line of the 
granite, however, the dip maybe considerably steeper, indicating the 
extent to which the Tertiaries have been involved in the general 
uplift of the main range. The axis of the Kern River anticline 
appeal's to lie in the valley of Poso Creek, but the minor undulations 
are so numerous that without detailed examination it is hazardous 
to say just where the center of the arch is situated. 
A study of the well records of this field points to the existence of a 
general body of sands and gravels from the surface to a varying 
depth up to 200 feet. Beneath this there is usually a stratum of blue 
clay, also varying in thickness from a few feet up to 100 feet. This 
clay is impermeable to the waters which nearly everywhere exist in 
the sands above. Below 1 lie clay in all wells is an alternation of sand 
and clay without regularity and varying in their relative thicknesses 
from point to point. These sands constitute the oil reservoir of the 
field, and as high as 400 or 500 feet, of them have been encountered 
in a single well. In a great many wells 200 or 300 feet of oil-bearing 
sand are found. Below the oil sands is another thin, blue clay, in 
which the casings are, as a rule, landed. Occasionally a well has 
perforated this, penetrating a water-bearing sand beneath, and in one 
or two instances holes have been carried to still greater depths, pene- 
trating a second clay underlying the oil sands, and finally passing 
into a mass of sand and gravel which yields an enormous amount of 
water. Many of the wells of this field at first flow, but sooner or 
later all require pumping. The production is from light up to 600 
barrels a day, according to the age of the well, its condition, and 
the amQunt of sand upon which the well has to draw. The gravity of 
the oil varies from 13° to 17° B., the lighter being found in the 
western portion of the territory. The color of the oil is black. 
)l 
