GEOLOGY AND PALEONTOLOGY OF PALOS - Pubs Warehouse

NORTHERN SAN PEDRO
In the northern part of San Pedro the Palos Verdes
sand is exposed in numerous street cuts and in some
natural exposures along the seaward edge of the terrace.
Wherever a street is cut below the level of the first ter­
race, the terrace platform and Palos Verdes sand, if
present, are exposed. Changes have been so numerous
since the current edition of the Wilmington topographic
map was issued that it is impractical to make the alter­
ations that would be necessary to show the present areol
geology; furthermore, the areal pattern is continually
changing. Alterations have been made at only a few
important localities. (See pi. 14.)
At places, even near the seaward edge of the terrace,
the Palos Verdes sand is lenticular and is locally absent,
as on the east side of Palos Verdes Street near Third and
on Ancon Street between First and Santa Cruz. At
many places west of Pacific Avenue the nonmarine cover
rests directly on the terrace platform. New cuts
farther west along First Street, between Grand and
Gaffey near the landward edge of the terrace, show,
however, pockets of fossiliferous sand and gravel.
Those cuts are not shown on the geologic map (pi. 1);
neither are outcrops of fossiliferous sand and gravel in
cuts along the extension of Gaffey Street into San Pedro
at the Elberon Street overpass.
Coarse-grained sand and gravel ranging in thickness
from a few inches to 8 feet are the prevailing lithologic
types in northern San Pedro. If only part of the forma­
tion is fossiliferous, that part is generally at the base.
On the west side of Beacon Street, northward from
O'Farroll, however, 1 to 3 feet of fossiliferous sand and
gravel composed of limestone cobbles overlie 3 to 8 feet
of barren brownish-gray sand at the base of the forma­
tion, as shown in the section on page 47. The following
section, measured on the west side of Pacific Avenue,
between Oliver and Bonita Streets (locality 112), is
representative of the sand-gravel facies:
Section of Palos Verdes sand on west side of Pacific Avenue, midway
between Oliver and Bonita Streets (locality 112)
Palos Verdes sand:
3. Fine-grained gray sand including stringers of
gray silty sand 1 to 10'inches thick. Grades
upward into overlying reddish-brown sand & '«
of nonmarine terrace cover._____________ 5 6
2. Fossiliferous moderately coarse-grained sand,
coarse-grained sand, and gravel (locality
112). Pebbles consist of limestone and
cherty shale and have maximum length of 7
inches; many limestone pebbles bored___ __ 12-19
Maximum thickness of Palos Verdes
sand____---_-_-_--__-_--------_. 7 1
San Pedro sand:
1. Moderately coarse-grained gray cross-bedded
unfossiliferous sand. Base not exposed. __ 9 6
Large shells of the gaper clam (Schizothaf.rus imt-
tallii), oriented in life position, siphon end upward,
may bo seen in their burrows on the south side of
Second Street between Pacific and Mesa and on the
west side of Center Street between Santa Cruz and
First. At the southeast corner of Third and Mesa
Streets transverse sections of burrows filled with Palos
Verdes sand and shells are visible in the San Pedro
sand 6 to 8 feet below the base of the Palos Vexdes.
On the west side of Beacon Street, 150 feet south of
Dreifus, a channel-filling lens of gravel at the base of
the Palos Verdes is 50 feet wide at the top, 15 feet wide
at the base, and 6 feet thick at the middle.
PLEISTOCENE SERIES 57
A beach facies, consisting of cross-bedded sand
containing worn and relatively small shells and shell
fragments, was formerly represented near the north­
west corner of Palos Verdes and Eighth Streets (lo­
cality 109), where the section given below was measured.
The strata at that locality have been removed recently,
and new outcrops nearby to the west represent the
usual sand-gravel facies.
Section of Palos Verdes sand in lot at northwest corner of Palos
Verdes and Eighth Streets (locality 1Q9)
Nonmarine terrace cover:
4. Reddish-brown sand.
Palos Verdes sand:
3. Shell fragments in matrix of cross-bedded fine­
grained sand__-____---___.-____________ 1 11-19
Cross-bedded fine-grained gray sand including
two, or locally three, 1-inch to 2-inch layers
of small worn gastropods (locality 109).
Thickness variable.____________________ 1 1
San Pedro (?) sand:
1. Gray sand.
Maximum thickness of Palos Verdes
In northeastern San Pedro, silty sand containing
a Macoma layer or layers overlies the usual fossiliferous
coarse-grained sand and gravel. The silty sand indi­
cates evidently more protected water than does the
underlying sand and gravel. MocoTna-bearing silty sand
was represented at Arnold's lumber yard locality (locality
113), 36 now destroyed. At that locality a basal fossili­
ferous gravel that varied in thickness but was as much as
6 feet rested on an uneven surface of cross-bedded San
Pedro sand having a relief of 1 to 2 feet. Silty sand
overlying the gravel included a Macoma layer a foot
above the top of the gravel. The following section,
measured on the west side of this remnant of the lowest
terrace, now destroyed, shows four Macoma layers in
a thickness of about 5 feet:
Section of Palos Verdes sand on east side of Harbor Boulevard
opposite Dreifus Street
Ft. in.
Nonmarine terrace cover:
6. Reddish-brown sand. Thickness estimated.... 20 0
Palos Verdes sand:
5. Brownish-gray silty sand including a 3-inch
Macoma layer at base...._________________ 1 7
4. Brownish-gray silty sand including a 4-inch to
5-inch Macoma layer at base___..___.____ 1 0
3. Brownish-gray silty sand including a 4-inch to
6-inch Macoma-"Paphia" layer at base._._ 1 5-8
2. Brownish-gray silty sanfl containing scattered
shells, mostly Macoma. ____________ _______ 2-6
1. Fossiliferous gravel.____'____________________ 2 2-7
Maximum thickmess of Palos Verdes sand.._ 7 4
The following section measured nearby, on the west
side of Harbor Boulevard at locality 114, also shows
a Macoma layer in silty sand.
Section of Palps Verdes sand on west side of Harbor Boulevard near
crossing of Pacific Electric tracks (locality 114)
Ft. in.
Nonmarine terrace cover:
4. Brownish-sand grading upward into reddish-
brown sand____________________________ 12 0
" Arnold, Ralph, op. cit., p. 27.
Ft.
6
In.