CRYSTALLINE ROCKS OF OAK HILL AREA 155 
Both sets of dikes have been faulted after the intrusion, the fault 
zones being common to both sets of dikes. Three of these fault zones 
may be seen in the quarry in addition to minor displacements; but 
the displacement in no case exceeds a few feet. Pyroxenite, gabbro, 
and serpentine fill the space between the dikes in the quarry. In a 
cut near the east side of Quarry Hill a large diorite dike in pyroxenite 
shows spheroidal weathering 
g, where the soft outer layers, which may 
Fic. 2.—Banded structure in olivine gabbro—Quarry Hill—common also to 
pyroxenite and norite. 
be easily removed, grade into extremely hard spherical cores. Other 
fine-grained dioritic dikes’ may be seen intruded into norite in an 
open cut on the north side of the top of Quarry Hill. Other scattered 
outcrops of diorite were found on Quarry Hill and over the north 
part of Oak Hill area, but no exposures have been observed to the 
south of the area nor in the Los Lagrimas Hills to the southeast. 
Petrographic characters.—The color of the hand specimen varies 
from a light to a dark gray, while the texture varies from very fine to 
rather coarse-grained, so that the commonest minerals, plagioclase 
and hornblende, may easily be seen with the naked eye. One of 
