SANTA CLARA VALLEY : SOUTHERN SULPHUR MOUNTAIN. 45 
OIL WELLS. 
The line of the suspected fault along the south side of Sulphur 
Mountain is marked in the several canyons by many strong seepages 
of petroleum, and in proximity to the fracture, in the northward dip¬ 
ping or more severely crumpled strata of the Fernando formation, 
most if not all of the wells of this general field are drilled. Those 
yielding the lighter oil, however, may penetrate to minor sands in the 
Modelo, or they may be peculiar to the brown shale of uncertain 
though perhaps Modelo age (p. 19). The heavier oil without doubt 
occurs in the Fernando formation. 
The wells in the field under discussion have been drilled at the heads 
of Aliso, Wheeler, Salt Marsh, and Adams canyons and along the bot¬ 
tom of a short gulch east of Adams Canyon. But little new develop¬ 
ment was under way at the time of the investigation and it was diffi¬ 
cult to obtain data relating to the occurrence of the petroleum. Fur¬ 
thermore, many of the wells were old and were abandoned, while the 
product of others was reduced to only 1 or 2 barrels a day. The initial 
flow of some of the wells appears to have been as high as 25 or even 
50 barrels. The depth as a rule ranges between 150 and 500 feet, but 
here and there 1,800 or 2,000 feet is said to have been attained. An 
early mode of recovering the oil was by tunnels, many of which pene¬ 
trate the shale of Sulphur Mountain. From these a small amount of 
oil still seeps, although several barrels a day have been obtained. 
Two varieties of oil occur in this field—one black, with a gravity of 
19° to 30° B.; the other green, with a gravity of 30° to 32° B. The 
lighter oil, as already stated, is believed to be associated with the 
shale doubtfully assigned to the Modelo formation. It occurs nearer 
the base of the mountain than the black and heavy oil. The com¬ 
paratively shallow depth of certain of the wells yielding green oil and 
their location well up on the slopes of Sulphur Mountain suggest the 
possibility that the productive beds outcrop in the base of the moun¬ 
tain. None of the strata, however, so far as the writer could learn, 
showed any indication of containing petroleum. 
The duration or life of the wells varies. Two years seems to be 
the maximum for the larger yields, but beyond this time the product 
dwindles to 1 or 2 barrels a day and then remains constant for an 
indefinite time. This constancy, coupled with the inexpensiveness of 
pumping, accounts for their still remaining in service. The earliest 
drilling reported in this field was done by Mr. Adams twenty-five 
years ago in Adams Canyon. This well and another in proximity, 
put down by the Union Oil Company, afforded a light oil, and a similar 
product was obtained by wells in Salt Marsh Canyon. Periodic 
attempts have been made to develop the source from which this sup¬ 
ply was derived, but without success. Opinions differ as to the rela¬ 
tions of the light oil to the Modelo shale. It is possible that this oil 
