Page 11 - dort1948
P. 11
Page 6
STRATIGRAPHY
Four sedimentary formations ot ~ertia17 age
occur within the area mapped, as shown in Plate I.
These are the Miocene Mint Canyon and Modelo tormationa,
the Pliocene Pico formation, and the Pl1o-Ple1stocene
Saugus formation. Also present are ~uaternary terraoe
deposits and valley-bottom alluvium. No igneous rooks
are exposed at the surface within the area of the map.
Any 11thologic criterion formulated to
difterent1ate between the strata in the mapped area is
almost certain to tail at one or more plaoes. In taot,
certain horizons within the tour bedrock formations are
commonly so similar ~hat spot 1dent1ficat1on 11
impossible, and recourse must be had to an ana.l7si1 of
the regional distribution and relations or the units.
The over-all l1tb.olog1e characteristics of the stratigraphic
aeries must be coupled with data from the few .fossil
localities. or with the scattered exposures ot angular
unoontormitiea to permit certain 1dent1t1oat1ons.
The laok of broadly applicable lithologic
charaoteristioa, as well aa the soaroity ot good expoeurea
in many parts ot the area. make an aoourate determination
