PUENTE HILLS : OLINDA FIELD. 
129 
of the wells but south of the syncline, extending from the region 
^ ^ the lore & oin to paragraph, include yellow and gray con- 
cretionaiy sandstone of the Puente type, with the associated siliceous 
shale and a succession of sandstone and arenaceous shale, also yellow 
and gray but apparently devoid of concretions and of the minor 
organic forms that characterize the Puente. There appear to be two 
formations in juxtaposition—one undoubtedly Puente, the other 
closely resembling the Fernando. Their relations suggest the locus 
of the Puente fault, a view strengthened by the sharp disturbance 
affecting the strata in the adjacent gulches. The strike of both 
formations is the same, about N. 70° W. The fault plane, on the 
whole, is believed to pass a short distance south of the northernmost 
of the Graham-Loftus wells, No. 17, but north of the others in this 
vicinity. With the exception mentioned, therefore, all the wells in 
this part of the field have apparently been drilled in the Fernando 
formation, and this view is borne out by the fact that conglomerate is 
encountered at various depths in the wells of both the Santa Fe and 
the Graham-Loftus companies. The position of these wells is believed 
to be on the northern limb of the subordinate anticline south of the 
fault. 
Outcrops of conglomerate and siliceous shale about 125 feet north¬ 
west of the Santa Fe No. 12 well may be regarded as locating the posi¬ 
tion of the main Puente fracture for this part of the field. The strike 
of the conglomerate ranges from N. 85° W. to east and west; the dip 
35°-40° N. The shale, as usual, shows large crumples for a consider¬ 
able distance from the fault. The westernmost well of the Santa Fe 
Company, No. 37, is close to the line of rupture, possibly a little to the 
north of it. 
The structure just described continues with some variation, not 
only to the west end of the field, but into Brea Canyon and the terri¬ 
tory north and south. The locus of the fault as it crosses the divide 
between the Olinda and Brea valleys is obscure, but it is not far from 
the point of least elevation. North of this point heavy beds of Puente 
sandstone lie in vertical or overturned position, bending, however, to 
a southerly dip of 20° or less as they pass to the summits of the hills 
above. South of the divide and for a mile or more along the southern 
slope of the ridge north of Brea Canyon the siliceous shale of the 
Puente outcrops. Although this shale is in natural sequence with the 
Puente sandstone on the north, it is believed that, on account of irregu¬ 
larities in adjacent areas, the two beds are separated by the Puente 
fault, or at least by a subordinate fracture. In Brea Canyon the syn- 
cline that in the Olinda field lies immediately north of the fault dis¬ 
appears, although other flexures in considerable number, among them 
a syncline of some importance, may be observed along the slope of the 
lulls to the west. 
