GEOLOGY. 
55 
It would be difficult to work out the limits of the area that this 
remnant covers. In all probability it is very small, and it has not 
been shown on the map. This shale here forms the base of the 
Fernando. A pebbly layer with constituent well-worn pebbles of 
Monterey shale embedded in sand has aided in the accumulation of 
asphalt on the summit of the ridge near by, where it probably marks 
the basal line of the Fernando formation. 
Above the soft diatomaceous or gritty shale and fine white sand 
that is common at or near the bottom of the Fernando the bulk of 
the formation is composed of rather loosely consolidated fine white 
and yellow sand and coarser gray sand that grades here and there 
into thick beds of loose conglomerate. The conglomerate is made 
of well-worn pebbles, mostly of flint and bard shale, embedded in a 
coarse sandy matrix. Locally the sand and conglomerate are ex¬ 
tremely hard, owing usually to the presence of a large number of 
mollusk shells from which a calcareous cement has been derived. 
The most prominent bed of conglomerate, and one that seems to be 
constant over the whole region, occurs from 800 to 1,000 feet up in 
the series (above the lowest horizon) just north of Canada de los 
Alisos, on La Laguna grant. What is probably the same bed is well 
exposed in cliffs west of Canada Laguna Seca, 1| miles south of the 
Los Alamos Valley. This loose aggregate of sand and pebbles in 
alternating strata of coarse and fine material is dominantly com¬ 
posed of the light-colored pebbles of Monterey shale. Pebbles of 
other varieties occur more sparingly. Above the conglomerate lies 
a stratum of limestone that is constant over the whole region and 
seems to mark a division in the Fernando. There are fwo or more 
massive beds of hard limestone interbedded with soft, gray, very 
alkaline, earthy material, making a total thickness ranging from 10 
to perhaps 50 feet. Its fossils indicate that it is of fresh-water 
origin, and possibly it marks the base of a fresh or brackish water 
series. The portion of the Fernando overlying this limestone prob¬ 
ably corresponds to the fresh-water Paso Robles formation of the 
Salinas Valley described by Fairbanks in the San Luis folio. In 
some places where this higher portion of the Fernando above the 
limestone has not been worn away, it is found to consist of little- 
consolidated beds of fine sand, gravel, and clay that look as if they 
might have been laid down in fresh water, but no proof of their 
origin has been found. Such beds are well exposed in the foothills 
of the San Rafael Range north of Santa Ynez, where they weather 
characteristically into cliffs at the summit of hills. A view of such 
an exposure is given in PI. VI, A (p. 46), which affords a good idea of 
the rough alternating beds of coarse material. No good lithologic or 
paleontologic criteria are known by which this series may be sepa¬ 
rated from the lower portion of the Fernando, and they are there¬ 
fore mapped as a unit. 
