88 
OIL DISTRICTS OF SOUTHERN CALIFORNIA. 
penetrate the Yaqueros sandstone, conglomerate, and shale, but 
whether any of the beds are duplicated it is impossible to determine. 
Such duplication may have taken place, but it has had practically no 
effect on the productiveness of the territory. The wells are located 
a little over a mile north northeast of the Torrey group, the geology 
of the two fields being quite distinct. 
Twenty-one wells were in operation or drilling at the time of the 
writer’s visit. They vary in depth from 600 to 1,200 feet, and the 
strata passed through, according to the logs, embrace sand, arena¬ 
ceous shale, dark, adobe-like clay, and the usual “hard shells” of the 
drillers. The character of the beds varies every 50 to 125 feet in 
depth, but sandstone predominates. Oil sand, so-called, appears to 
be encountered at depths of 540 to 620 feet. Water is found both in 
the upper parts of the wells and beneath the lowermost oil sand re¬ 
corded. Well No. 20, of the group at the turn of the canyon, is the 
only one in which pebbles are reported. These are, perhaps, a local 
development of one of the more prominent sandstones that lie near 
either the summit or the base of the Yaqueros beds. Usually but a 
single oil sand shows in a well, and it is the opinion of the superin¬ 
tendent that the producing horizon is the same throughout the field. 
The gravity of the oil averages, it is said, 24° B., but in some 
instances rises to 26°. This difference, as compared with the Torrey 
oil, is inexplicable, for both are believed to be derived from the same 
formation. Their horizons, however, may be different, and in the 
Eureka field the sediments appear to be coarser, while the strata are 
far more fractured, if the interpretation of the geology here given is 
correct. The latter feature would tend to permit the easier escape of 
the lighter hydrocarbons, leaving behind the heavier oils, which now 
constitute the product. 
The yield has been from 1 to 40 barrels per day. The field has, 
however, never been one of large production, but from the records the 
wells appear to have maintained their supply with remarkable uni¬ 
formity. The log of one of these wells is appended: 
Lo<j of well in Eureka Canyon. 
Thick¬ 
ness. 
Depth. 
Sandy shale and “adobe”. 
Feet. 
Feet . 
50 
Gravel, with water. 
25 
75 
Dark, black ‘ ‘ adobe ”. 
Arenaceous shale. 
125 
475 
Soft sand. 
50 
595 
Blue, caving shale, with thin sands interlaminated, becoming solid at .iso feet 
35 
570 
“Hard shell,” this marking the top of the oil sand, according to the driller’s statement 
At this point, also, water is shut off... 
15 
10 
5R5 
Oil sand. 
505 
Water sand with gravel distributed through it (abundance of water, no oil) 
245 
1 AO 
840 
i non 
Soft, blue sandy shale. 
Coarse gravel (water). 
197 
1,127 
