HomeMy WebLinkAboutCT 99-04; VILLAGES OF LA COSTA OAKS & RIDGE; PALEONTOLOGICAL RESOURCES LETTER; 1999-07-07r
SAN DIEGO NATURAL HISTORY MUSEUM
BALBOA PARK -SAN DIEGO SOCIETY OF NATURAL HISTORY -ESTABLISHED 1874
7 July 1999
Ms. Sarah Patterson
Morrow Development
P.O. Box 9000-685
Carlsbad, CA 92018-9000
RE: Paleontological Resources: La Costa Greens, La Costa Ridge, La Costa Oaks
Dear Sarah:
This letter report summarizes the results of my paleontological resource
assessment of the above referenced project sites. The report is based upon a review of
existing published and unpublished geological literature (Weber, 1963; Wilson, 1972;
Eisenberg and Abbott, 1985), a review of museum paleontological records (San Diego
Natural History Museum), and a walkover of the project site (6 July 1999) to field check
the results of the literature and record reviews. Separate discussions are provided below
for the three different projects.
La Costa Greens -The La Costa Greens project site is located east of El Camino
Real, north of Alga Road, and south of Palomar Airport Drive. The project site occupies
a broad alluvial valley with dissected mesa lands forming the western slopes and steeper
volcanic foothills forming the eastern slopes. Bedrock exposures are limited because of
existing improvements (a portion of the La Costa Golf Course occupies the valley floor),
prior agricultural use, and native vegetative cover. The highest point on the project site
(approximately elevation 420 feet) is located in the southeast comer adjacent to existing
residential development. The lowest point (approximately elevation 80 feet) is located
on the valley floor adjacent to Alga Road.
According to existing geological reports the geology of the site consists of early
Cretaceous-aged ( 125 million years old) meta volcanic rocks (Santiago Peak Volcanics)
and middle Eocene-aged ( 42-48 million years old) claystones and sandstones (Delmar
Formation, Torrey Sandstone, Friars Formation, Scripps Formation).
The Cretaceous metavolcanic rocks are confined to the southeastern portion of the
project site. During the field walkover, exposures of these rocks were seen to consist of
well indurated volcanic breccia. No fossils were observed in the limited bedrock
exposures Cretaceous rocks and no previous fossil collecting localities are recorded for
the project site. In addition, because of their "fiery" origin, these volcanic breccias are
typically unfossiliferous.
Except for the Holocene alluvium on the valley floor, the remainder of the project
site is underlain by Eocene sedimentary rocks. During the field walkover, exposures of
these rocks were seen to consist of interbedded layers of green claystone, light yellow
fine-grained sandstone, and light gray coarse-grained pebbly sandstone. Existing
geological reports assign these Eocene rocks to either the Delmar Formation and Torrey
Post Office Box 121390 * San Diego, California 92112-1390 * Telephone 619-232-3821 * FAX 619-232-0248 * www.sdnhm.org
. .
Sandstone (Wilson, 1972) or the Delmar Formation-Friars Formation undifferentiated
and Scripps Formation (Eisenberg and Abbott, 1985). No fossils were observed in the
limited exposures of Eocene rocks and no previous fossil collecting localities are
recorded for the project site. However, significant Eocene fossil collecting localities are
recorded within a one mile radius of the project. These records suggest a high potential
for the exposure of significant paleontological resources during future construction-
related mass excavation work proposed for the project site.
Mitigation of the predicted construction-related impacts can be accomplished
through implementation of a paleontological resource mitigation program. This program
should include the following elements:
[ 1] attend any pre-construction meetings;
[2] monitoring on a full-time basis all grading operations in the Eocene
sedimentary rocks and inspect cuts for unearthed fossil remains;
[3] salvage remains as they are uncovered;
[ 4] screen wash selected sites (if discovered) for recovery of small fossil remains;
[5] document the stratigraphic and geologic context of salvaged fossil remains;
[6] remove fossils from the project site;
[7] clean, repair, and sort salvaged fossils for eventual donation to an accredited
institution such as the San Diego natural History Museum:
[8] prepare a final report summarizing the results of the mitigation program. This
report will include a discussion of methods employed, fossils recovered, geologic
context of fossil remains, and significance of mitigation program.
La Costa Ridge -The La Costa Ridge project site is located south of Alga Road,
west of Rancho Santa Fe Road, northwest of San Marcos Creek, and east of El Fuerte
Street. The project site consists of a rugged volcanic and plutonic terrain with the steep-
sided gorge of San Marcos Creek forming the eastern and southern boundaries of the
project site. The gorge (including Box Canyon) provides spectacular bedrock exposures.
Other portions of the project site, however, are covered by native vegetation. The highest
point (approximately elevation 738 feet) is located in the northern portion of the project
site. The lowest point (approximately elevation 80 feet) is located at the mouth of Box
Canyon.
According to existing geological reports (Weber, 1963; Eisenberg and Abbott,
1985) the geology of the site consists of early Cretaceous-aged (125 million years old)
metavolcanic rocks (Santiago Peak Volcanics) and early to late Cretaceous-aged (125 to
90 million years old) coarse-grained plutonic rocks (Peninsular Range Batholith).
The Cretaceous meta volcanic rocks underlie the southern half of the project site,
while Cretaceous plutonic rocks underlie the northern half of the project site. No
previous fossil collecting localities are recorded for the project site. The "fiery" origin
of the metavolcanic and plutonic rocks indicates that these rock units are unfossiliferous
and have a zero paleontological resource potential.
Because of the zero paleontological resource potential of the project site, there
will not be any impacts and therefore no necessity for implementation of a
paleontological resource mitigation program.
La Costa Oaks -The La Costa Oaks project site is located south and southeast of
San Marcos Creek, west of unicorporated county land, and north of City of Encinitas
land. Rancho Santa Fe Road roughly bisects the project site in a north-northeast
Post Office Box 121390 • San Diego, California 92112-1390 * Telephone 619-232-3821 * FAX 619-232-0248 * www.sdnhm.org
direction. The project site consists of a rugged volcanic and plutonic terrain with the
steep-sided gorge of San Marcos Creek forming the northeastern boundary of the project
site. The highest point (approximately elevation 980 feet) is located in the eastern
portion of the project site. The lowest point (approximately elevation 360 feet) is located
in the gorge of San Marcos Creek.
According to existing geological reports (Weber, 1963; Eisenberg and Abbott,
1985) the geology of the site consists of early Cretaceous-aged ( 125 million years old)
metavolcanic rocks (Santiago Peak Volcanics) and early to late Cretaceous-aged (125 to
90 million years old) coarse-grained plutonic rocks (Peninsular Range Batholith).
The Cretaceous metavolcanic rocks underlie the southern three-quarters of the
project site, while Cretaceous plutonic rocks underlie the northern one-quarter of the
project site. No previous fossil collecting localities are recorded for the project site. The
"fiery" origin of the metavolcanic and plutonic rocks indicates that these rock units are
unfossiliferous and have a zero paleontological resource potential.
Because of the zero paleontological resource potential of the project site, there
will not be any impacts and therefore no necessity for implementation of a
paleontological resource mitigation program.
In summary, the La Costa Greens project site has a high paleontological resource
potential that will require implementation of a paleontological resource mitigation
program during construction. The La Costa Ridge and La Costa Oaks project sites have
zero paleontological resource potentials and will not require mitigation programs during
construction.
If you have any questions concerning this report, please feel free to contact me at
(619)232-3821, ext. 232.
Sincerely,
/
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Thomas A. Demere, Ph.D.
Curator, Department of Paleontology
Director, Department of Paleontological Services
References Cited:
Eisenberg, L.I., and P.L. Abbott. 1985. Eocene lithofacies and geologic history, northern San Diego
County. In, P.L. Abbott (ed.), On the Manner of Deposition of the Eocene Strata in northern San
Diego County. San Diego Association of Geologists, fieldtrip guidebook, pp. 19-35.
Weber, F.H., Jr. 1963. Geology and mineral resources of San Diego County. California Division of Mines
and Geology, County Report 3:1-309.
Wilson, K.L. 1972. Eocene and related geology of a portion of the San Luis Rey and Encinitas
quadrangles, San Diego County, California. Unpublished M.A. thesis, University of California,
Riverside, 135 p.
Post Office Box 121390 * San Diego, California 92112-1390 * Telephone 619-232-3821 * FAX 619-232-0248 * www.sdnhm.org