GEOLOGY OF THE SOUTHERN COAST RANGES 571 
The quartz basalt occurs in the form of dikes intruded at the 
base of the Miocene east of Edna. The larger one is nearly 
continuous, following the strike of the rocks for two and one- 
half miles. The rock is dark and fine grained with a few scat- 
tering phenocrysts of labradorite feldspar. The most important 
phenocrysts are quartz scattered in a fairly uniform manner 
through the rock. The quartz grains show the effects of corrosion 
and are surrounded by augite microlites. The analysis shows 
that the rock has a rather low percentage of hme, but there can 
be no doubt that it belongs among the basalts. 
Other Tertiary basalts occur on a small scale at several dif- 
ferent points, but they have no striking features and will not be 
described here. It is impossible to determine the relative ages 
of these basic igneous rocks, although it would seem that with 
the exception of the rhyolite they followed the disturbances 
which folded the Miocene. 
STRUCTURAL GEOLOGY. 
Nearly all the structural features have a linear arrangement 
along northwest and southeast lines. The mountains are struc- 
turally synclines elevated by comparatively recent movements, 
the most important being faulting. This region may be divided 
in a general way into five crustal blocks, as follows, beginning 
on the north: the granite and-associated rocks north of the 
Salinas Valley, the depression occupied by the Salinas Valley, 
the Santa Lucia range, the western foothills of this range and 
the broad valleys at its southern base, and last, the San Luis 
range. Each of these blocks has behaved as a unit since Mio- 
cene, or in several cases very much earlier times. All the fault- 
ing now recognizable dates from later Neocenetime. The Santa 
Lucia range constitutes a remarkable fault block. It has been 
elevated, not by a single fault on each side, but in most places 
by several forming step faults. A fault line follows the lowest 
portion of the Salinas Valley, and other lines of folding and 
faulting are to be seen along the northern slope of the Buchon 
range. 
