62 SANTA MARIA OIL DISTRICT, CALIFORNIA. 
be called—is composed of bowlders, pebbles, and fragments of Mon¬ 
terey flint and shale, besides pebbles of other rocks in smaller quan¬ 
tity. Some of the pebbles are very much waterworn, but in places 
the number of unworn fragments of shale almost necessitates the use 
of the word “breccia” in describing the deposits. Evidence of bed¬ 
ding is rarely prominent in the typical terrace deposits, but they 
invariably appear to lie horizontal, seeming to have been little dis¬ 
turbed by the uplift of the land that brought them to their present 
elevation. 
No fossils have been found in these deposits, but they contain 
numerous pholas-bored pebbles of Monterey shale, and in places, as 
on Burton Mesa, the Monterey shale itself, upon which the deposits 
lie, has been bored by these marine mollusks. 
Many of the cappings formed parallel with the surface through 
hardening by iron oxide have the appearance of being beds with 
appreciable dip, and are therefore misleading. The thickness of the 
coating of Burton Mesa is 25 or 30 feet and the cover of the typical 
terrace in other parts of the region has about the same thickness. 
Whether it attains a much greater development than this at any 
place is hard to tell. These shallow coverings hide considerable areas 
of the Monterey and obscure its structure, but most of the canyons 
that cut into the terraces reveal the presence of the oil-bearing for¬ 
mation beneath. The thickness of the coatings is not sufficient to 
make a serious difference in the depth to which it is necessary to 
drill for oil. The deposits are economically of importance as reser¬ 
voirs for the oil escaping from the Monterey shale, and thus they 
give rise to accumulations of asphalt. It is usually impossible to 
tell whether the sand that helps to form the asphalt is a terrace 
deposit or belongs to the Fernando. The terrace sand can not form 
as deep asphalt deposits as those due to the Fernando sand. 
In some of the valley fillings above mentioned, as for instance along 
Salsipuedes Creek, and at the west edge of the Santa Maria Valley 
between Guadalupe Lake and the Casmalia Hills, there occur hori¬ 
zontally bedded deposits of clay, sand, and gravel differing in ap¬ 
pearance from the terrace deposits and possibly differing in age and 
origin. A good example of an old valley filling which now forms the 
summit of a hill is shown in PI. IV, B (p. 36). It consists of a sandy 
and earthy material through which rock fragments and pebbles are 
scattered. It illustrates the usual unconformity of the post-Fernando 
deposits with the older formations. The low hills in the region of 
Santa Ynez are formed largely of horizontal beds of fine gravel 
unlike the Pleistocene deposits found elsewhere. These exhibit in 
one place an appearance of being tilted, though this may be due to 
cross-bedding. 
