108 
VARIOUS LOCALITIES OF ASPHALTUM. 
asphaltic rocks lie beneath high water mark, and are visible at low water ; nor is the effusion 
of bitumen from submarine localities confined to this district. The waters of the Santa Bar¬ 
bara channel are frequently covered with a thin layer of liquid bitumen, which is gradually 
inspissated by the evaporation and effect of solar heat, and then washed ashore in solid masses 
by the tide; the whole atmosphere of the sea, many miles out, being highly impregnated with 
the bituminous odor. These phenomena (the odor and surface film) were observed by the 
writer on two several occasions in sailing between San Diego and San Luis Obispo. It has 
also been observed still further out at sea by Lieut. Trowbridge,* U. S. A. It has not, how¬ 
ever, been observed along the route of the Panama mail steamers, whose track lies considerably 
west of the islands off Santa Barbara shore, so that it may be inferred that the greater amount 
of upheaving action which evolves bitumen lies between these islands and the coast. 
This substance exists in all the stages of consistence, from that of a thin syrup to that of 
ordinary coal. In some deposits, as along the Buenaventura river, all of these are found 
together ; also along Tar creek, a tributary of the Santa Clara ; in fact, wherever the bitumen 
is oozing at the present moment there the substance is fluid and thin. The quantity of the 
mineral is incalculably great in the several deposits, and the supply appears to be steady, 
although not abundant in the majority of the localities. The characteristics of each locality 
will be briefly alluded to in detail. 
1. The bitumen of the Santa Cruz mountains , near the Pajaro river. —It is here found on the 
banks of the Arroyos La Brae and Pescadero. As many as six springs were found close to the 
banks of these two creeks, which cut their way through soft brown fossiliferous sandstone. 
The ground for several yards round each spring was covered with the solidified mineral, and, 
perhaps, twenty-five acres in all were occupied by the overflow. The fluidity of the bitumen 
at the immediate spring was not very great; not far distant from these is the igneous rock of 
the Santa Cruz range, serpentine and trap, (greenstone,) which is directly in contact with the 
tertiary sandstone, the latter is metamorphic near the point of contact. 
2. Bitumen of San Luis valley. —This deposit is situated about four miles southwest of the 
village of San Luis Obispo, along the road leading down the river to the port. The road, as it 
leaves the valley, passes between a series of low hills, which cut off the valley from the shore. 
About half a mile below the ranch Corral de Piedras, which is located close to the edge of the 
valley, the asphalt is met with in situ. The rock is a fine quartzose sandstone of a brownish 
color, and decaying under the finger, darker on the surface than inside, and forming a pepper- 
gray colored soil; this bed is not fossiliferous. The strike, north 70° west, crosses the road, 
the rock dipping southwest 20°. The bitumen here oozes out from the rock fissures, and 
is spread over a space of 350 yards from the creek; one opening has a basin diameter of 
30 inches; 8 inches below the surface is the well of bitumen, which rises and flows over the 
edge, coursing down toward the creek in a small stream, which solidifies some distance below, 
forming a layer of pitchy hardness, over which the fresher outflow wends its way. Another 
spring, 20 inches in diameter, resembles the former, being a hole in the superficial sand rock. 
This well has the bitumen in a more fluid condition ; a six foot pole was pushed down through 
the centre of this fluid mass, and found its way readily until, from its pliancy, it no longer 
resisted pressure. The liquid hardens readily at the edges of the spring and on the soil around, 
which is partially liquified by the mid-day sun, rendering it plastic, but not fluid. A third 
spring close by gave off carburetted hydrogen gas, which was inflamed and burned brilliantly 
* On the authority of Dr. Trask’s “ Report on Geology of Coast Mountains.” 
