DETAILS OF THE DEVELOPED TERRITORY. 107 
distance of 1,100 feet in one well. Either water sand, dry oil sand, or 
limy “shell” usually defines the base of the productive zone. 
THE OIL. 
Two grades of oil are struck in this field, one a black oil with a 
gravity of 18° to 24°, the other a brown to greenish oil of about 35° 
Baume. The black oil is produced by most of the wells, the 
lighter variety coming only from the Logan well of the Los Alamos 
Oil and Development Company and the No. 3 Wise & Denigan well 
of the Union Oil Company. The relations of occurrence of the two 
grades are not known. One of the wells yields an emulsion of water 
and 20° oil, which is reddish brown in color as it comes from the well. 
This oil turns to the usual black color on separation of the water by 
settling. 
PRODUCTION. 
The production of the individual wells ranges from 100 to 1,000 
barrels per day, the best producers averaging from 300 to 500 barrels. 
One of the wells which gave an initial output of 200 to 300 barrels at 
first, suddenly began flowing 1,000 barrels per day. This continued 
for a few days and then gradually fell off to 300 barrels, which it is 
still yielding. It is said that the wells, as a rule, are exceptionally 
steady producers, falling off but little in the two years since the field 
was first opened. A ery few of the wells have been tried to their full 
capacity, so that it is probable that yields greater than those men¬ 
tioned will be recorded when the field is fully tested. 
ARROYO GRANDE FIELD. 
LOCATION. 
Drilling has recently shown that at least certain portions of the 
region north and northwest of Arroyo Grande, in the San Luis quad¬ 
rangle, San Luis Obispo County, a short distance north of the area 
shown on PI. I, are underlain by productive oil formations. The 
successful wells belong to the Tiber Oil Company, and are located on 
the west side of Price Canyon about 3 miles northeast of Pismo and 
7 miles slightly east of south of San Luis Obispo. Although outside 
of the immediate area covered by this report the occurrence is so 
important in showing an extension of the Santa Maria district toward 
the northwest as to merit mention here. 
GEOLOGY. 
The geology of the San Luis quadrangle has been mapped and 
described by II. W. Fairbanks in .the San Luis folio. a According to 
a Copies of this folio, which is No. 101 in the series making up the Geologic Atlas of the United States, 
should be in the hands of every oil man or other person interested in the natural resources of this region; 
it may be obtained for 25 cents from the Director of the United States Geological Survey, Washington, 
D. C. 
