I eldridge.J PETROLEUM FIELDS OF CALIFORNIA. 309 
proximity to the fault referred to above, and is also stained with bitu- 
men. 
The structure of the McKittrick district is that of a sharp anticline, 
en echelon with adjacent anticlines of the range. Along its axis is 
developed the fault mentioned, which locally is of the nature of an 
overthrust, the siliceous shales of the Monterey west of the plane being 
pushed up well over the sands, conglomerates, and clays of the San 
Pablo. While this fracture and fold, along which most of the produ- 
cing wells of the district are located, are the most important of the 
region, other folds and faults exist in lines parallel with these, and at 
either end of the district one or another of them may become the chief 
fissure, j'et apparently, so far as is at present known, without especial 
accumulation of petroleum. Of the overthrust nature of the main 
fold interesting evidence exists in the material that is brought up by 
the bailer in drilling — not only sands more or less saturated with oil, 
but pebbles characteristic of the San Pablo. Conspicuous among the 
latter are those of siliceous shale of the Monterey type, bearing foram- 
iniferal remains, fish scales, and pholas borings. A noteworthy fea- 
ture of the line of disturbance for several miles, both northwest and 
southeast of McKittrick, also, are the dikes of sandstone richly impreg- 
nated with bitumen. These vary in length from a few feet to a half 
mile or more, and in width up to 10 or 15 feet; their depth, of course, 
is unknown. Gash veins of high-grade asphalt also occur. 
The productive oil wells of this district for its entire length lie 
within a zone less than a quarter of a mile wide, and in places less 
than 200 feet wide. Their depth varies from 200 to 1,500 feet, the 
shallower holes being in the center of the field, opposite McKittrick. 
The yield is from a few up to 700 barrels, the latter exceptional. 
In gravity the oil varies between 11° and 17° B. While the narrow, 
productive zone is persistent in the general directness of its trend — 
about N. 60° W. — it is, nevertheless, somewhat undulating, according 
as the axis of crumpling or faulting varies. 
SUNSET DISTRICT. 
This district lies in the southwest corner of the San Joaquin Valley, 
along the eastern base of the San Rafael Range, about 35 miles in a 
direct line southwest of Bakersfield, with which it is now connected 
by a branch of the Atchison, Topeka and Santa Fe Railway. It. is 
also distant from the McKittrick district about 25 miles, but recent 
developments in the Midway field, the northwestern extension of the 
Sunset, are gradually diminishing this gap. The Sunset field, like 
those to the northwest, is developed in the lower foothills of the 
Coast Range. The physical aspect of the region is that of moderately 
rugged mountains, 3,000 to 4,000 feet in altitude, bordered by a desert. 
The formations involved in the geology of the district include, in 
the higher portions of the adjacent range, a great series of massive, 
