GEOLOGY. 
53 
Barbara County, where it was deposited in the old basin between the 
Santa Tnez and San Rafael ranges. It covers up the Monterey 
over the greater part of the basin, and as its structure in most places 
there conforms approximately to that of the Monterey, it is a fairly 
good key to the folding that has taken place in this underlying 
formation. The relation between the Monterey and Fernando is of 
a somewhat perplexing nature. An unconformity in dip between 
the two was not to be definitely made out on examination of the 
exposed contact in any part of the central basin, because of the 
fact that the Monterey and Fernando were subjected practically to 
the same movements over a large part of the region. Lithologic 
similarity of parts of the Fernando to the Monterey is also an obstacle 
to their differentiation. But pebbles of Monterey shale and flint, 
showing here and there pholas borings and giving evidence of marine 
deposition, are abundant in the Fernando. In fact, the greater part 
of the coarse detrital material of the Fernando conglomerate is 
c 
derived from the Monterey, proving that its period of deposition 
was one of erosion in the previously deposited shale, that it followed 
the uplift above sea level of a portion of the Monterey, and that it 
was subsequent to the formation of the flint in that shale series. 
The importance of the break between the two is indicated by the 
change in character of the deposits from organic, probably deep¬ 
water sediments almost free from erosional debris to sandy and 
gravelly deposits derived from the wearing away of hard land areas. 
This change was hardly as marked as that occurring in the reverse 
order at the close of Vaqueros time, although it accompanied what 
was probably a greater time and structural break. The apparent 
structural conformity between the Monterey and Fernando at most 
places within the basin region is probably due to the previously 
almost undisturbed attitude of the shale upon which the Fernando 
was laid down and the subsequent disturbance of both formations 
at the same time. But remnants of the Fernando left around the 
border exhibit less conformity with the underlying Monterey, owing 
doubtless to the fact that the shale of the latter was upheaved around 
the edges of the basin to form the mountains bordering it during 
the period intervening between the close of Monterey time and the 
beginning of deposition of the Fernando. 
The chief importance of the Fernando in connection with studies 
of this oil field is derived from the facts that it hides the oil-bearing 
formation over a wide area; that it affords through its structure, 
however, a clue to the structure of the underlying Monterey; and 
that it acts as a reservoir for oil (Arroyo Grande field) and as a recep¬ 
tacle for escaping bituminous material. In the last-mentioned way 
it gives origin to asphalt deposits of economic value and to cappings 
of hard asphalt that may be of significance as an aid in the retention 
of the oil within the Monterey. 
