HomeMy WebLinkAboutApn F2 - PaleontologicalAPPENDIX F2
Paleontological Resources Assessment
TECHNICAL REPORT
PALEONTOLOGICAL RESOURCE ASSESSMENT
OTAY RANCH – PARCEL B – VILLAGE 8 WEST
CITY OF CHULA VISTA
SAN DIEGO COUNTY, CALIFORNIA
Prepared for:
OTAY LAND COMPANY
1903 Wright Place
Suite 220
Carlsbad, California 92008
Prepared by:
DEPARTMENT OF PALEOSERVICES
SAN DIEGO NATURAL HISTORY MUSEUM
P.O. Box 121390
San Diego, California 92112
Thomas A. Deméré, Ph.D., Director
Sarah A. Siren, M.S., Paleontological Field Manager
2 September 2010
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TECHNICAL REPORT
PALEONTOLOGICAL RESOURCE ASSESSMENT
OTAY RANCH – PARCEL B – VILLAGE 8 WEST
CITY OF CHULA VISTA
SAN DIEGO COUNTY, CALIFORNIA
INTRODUCTION
Otay Land Company proposes to develop an approximately 300-acre site in the City of Chula
Vista, San Diego County, California. The parcel is located at the southern extent of La Media
Road, southwest of the intersection between Santa Luna Road and Magdalena Avenue (Figures 1
and 2).
This technical report provides an assessment of issues related to paleontological resources within
the project area, including proposed offsite trails and utility corridors. The purpose of this report
is to assist Otay Land Company in planning and design efforts for the purposed project as related
to paleontological resource issues. Specifically, this report is intended to summarize existing
paleontological resource data in the project area and vicinity; assess potential impacts to
paleontological resources from development of the project area; and identify mitigation measures
to avoid or reduce project-related impacts wherever feasible. Additional discussion of report
methodology is provided below. This report was prepared by Sarah A. Siren and Thomas A.
Deméré of the Department of PaleoServices, San Diego Natural History Museum (SDNHM), San
Diego, California.
As defined here, paleontological resources (i.e., fossils) are the remains and/or traces of
prehistoric (i.e., 10,000 years or older) plant and animal life exclusive of humans. Fossil remains
such as bones, teeth, shells, leaves, and wood are found in the geologic deposits (rock
formations) within which they were originally buried. For the purposes of this report,
paleontological resources can be thought of as including not only the actual fossil remains but
also the collecting localities and the geologic formations containing those localities.
METHODOLOGY
A review was conducted of relevant published and unpublished and published geologic reports
(Kennedy and Tan, 1977; Tan and Kennedy, 2002), published and unpublished paleontological
reports (Deméré, 1988; Walsh and Deméré, 1991; Deméré and Walsh, 1993), and museum
paleontological locality data (SDNHM, Department of Paleontology). This approach was
followed in recognition of the direct relationship between paleontological resources and the
geologic formations within which they are found. Knowing the geology of a particular area and
the fossil productivity of formations that occur in that area, it is possible to predict where fossils
will, or will not, be encountered.
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Figure 1. Portion of the geologic map of Tan and Kennedy (2002) showing the Parcel B - Village 8 West project
boundaries (black rectangle) and offsite improvements (extending beyond black rectangle in red south
of the property boundary). The majority of the project area is underlain by sedimentary rocks of the
Oligocene-age Otay Formation (To). Quaternary-age (late to middle Pleistocene) alluvial and terrace
deposits (Qoa) occur in the southeast portion of the project site, while Jurassic-Cretaceous-age Santiago
Peak Volcanics (KJmv) occur in the southwest portion of the project site. Other rock units identified on
the map include: late Holocene active channel and wash deposits (Qw), Holocene alluvial deposits
(Qya), middle to early Pleistocene alluvial deposits (Qvoa), Oligocene to Miocene fanglomerate facies
of the Otay Formation (Tof). Base map; Otay, CA 7.5’ USGS topographic quadrangle; scale 1:24,000.
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A pedestrian survey of the project and immediately surrounding areas was conducted on
September 23, 2009, by SDNHM personnel to field check the results of the literature and record
searches and to determine the paleontological resource sensitivity of the geologic units that will
be affected by the proposed development. This work involved inspection of bedrock outcrops for
exposed paleontological resources.
EXISTING CONDITIONS
PHYSICAL GEOLOGICAL SETTING
In general, Parcel B - Village 8 West lies within the southern portion of the Peninsular Ranges
Geomorphic Province, which is dominated by plutonic igneous rocks of late Mesozoic age (~125
to 90 million years old [Ma]) and pre-batholithic metamorphic rocks of middle Mesozoic age
(~200 to 140 Ma). Along the coastal plain of San Diego County these crystalline basement rocks
are overlain by younger sedimentary deposits of Cenozoic age (~50 Ma to 10,000 years old)
(Walawender, 2000).
The oldest geologic units on site are the Jurassic-Cretaceous-age Santiago Peak Volcanics which
are mapped in the southwestern portion of Parcel B - Village 8 West (Kennedy and Tan, 1977;
Tan and Kennedy, 2002; Figure 3). This area includes Rock Mountain, a crystalline basement
outlier composed of metavolcanic rocks. Rock Mountain has been the site of commercial quarry
operations for decades. In the southeastern portion of the project site, poorly consolidated
Quaternary-age sedimentary rocks crop out (Kennedy and Tan, 1977; Tan and Kennedy, 2002;
Figure 6). These relatively youthful river terrace deposits date back to the Pleistocene Epoch (Ice
Age) and rest on much older sedimentary rocks mapped as the Oligocene-age Otay Formation
(~29 Ma; Artim and Pickney, 1973; Deméré, 1988; Walsh and Deméré, 1991; Tan and Kennedy,
2002), which underlie the majority of the project site.
Natural outcrops of the Otay Formation are limited because of a pervasive cover of plant material
and topsoil. However, artificial exposures along the San Diego Aqueduct right-of-way were
observed in the east central portion of the project study area (Figures 4 & 5).
PALEONTOLOGICAL RESOURCE ASSESSMENT
The following section provides a general overview of the types of geologic deposits located
within the project area and proposed offsite trails and utility corridors.
Stratigraphic Rock Units
Santiago Peak Volcanics (KJmv)
Description:
The metavolcanic rocks mapped by Tan and Kennedy (2002) as the late Jurassic to early
Cretaceous-age Santiago Peak Volcanics are the oldest geological rocks on site. The Santiago
Peak Volcanics, located in the southwestern portion of the project site, are mainly composed of
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volcanic breccias, with lesser amounts of volcanic tuffs and flows (Tan and Kennedy, 2002). In
other parts of the region, slightly-to-moderately metamorphosed marine mudstones and
sandstones appear to be interbedded with the volcanic rocks (Fife et al., 1967). Radiometric
dates on the volcanic flow-rocks of the Santiago Peak Volcanics have yielded earliest Cretaceous
ages, approximately 120-130 Ma (Herzig and Kimbrough, 1991). The Santiago Peak Volcanics
were altered during emplacement of the vast volumes of magma generated by early Cretaceous
subduction of a large lithospheric plate. These magmas subsequently cooled to form the plutonic
(“granitic”) rocks of the Peninsular Ranges Batholith, which forms the bulk of the central
mountainous region of San Diego County.
Figure 3. Metavolcanic rocks of the Santiago Peak Volcanics, as mapped by Tan and Kennedy (2002), are present
in the southwestern portion of Parcel B - Village 8 West. Bedrock bouldery outcrops are visible at the
surface (right side of the photo; view south along the southwestern portion of Parcel B - Village 8 West).
Paleontology:
In general, the molten origin of the Santiago Peak Volcanics precludes the possible discovery of
fossil remains in these rocks. However, some of the volcanic breccias contain petrified wood, as
in Mira Mesa and near Rancho Santa Fe (D'Vincent, 1967). In addition, certain exposures of the
metasedimentary portion of this formation have produced important remains of siliceous
microfossils (e.g., radiolarians: Jones and Miller 1982) and marine macroinvertebrates including
belemnites and clams (Jones and Miller, 1982). There are currently no records of any
paleontological collecting sites in these rocks as exposed south of San Clemente Canyon in the
City of San Diego. Field inspection of outcrops of the Santiago Peak Volcanics indicated that
only metavolcanic rocks occur in the project area.
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Site Specific Assessment:
Because the outcrops of the Santiago Peak Volcanics within the study area consist of exposures
of metavolcanic rock, this rock unit has been assigned a zero paleontological resource sensitivity.
Otay Formation (To and Tof)
Description:
The sedimentary rocks underlying the majority of the project area have been mapped by Tan and
Kennedy (2002) as fluvial and alluvial fan strata of the Oligocene-age Otay Formation. The Otay
Formation in this area is correlative with the Arikareean North American Land Mammal Age and
has been radiometrically dated at approximately 29 Ma. The formation has been divided into
three members by Walsh and Deméré (1991) who recognize a basal angular conglomerate
(fanglomerate) member, a middle gritstone member, and an upper sandstone-mudstone member.
Typical exposures of the upper member consist of gray-white, medium-grained, tuffaceous
sandstone, with interbeds of brown and red-brown claystones and white bentonite layers (Walsh
and Deméré, 1991). The middle member consists of interbedded coarse-grained sandstones and
angular gravels (gritstone). The lower member is a poorly-sorted, cobble to boulder
fanglomerate (Tof of Tan and Kennedy, 2002; Figure 1). In general the formation becomes finer
grained from bottom to top with the basal angular conglomerate member grading upward and
westward into the gritstone member, which in turn grades upward and westward into the
sandstone-mudstone member. Taken together, the Otay Formation may be as much as 400 feet
thick, but at any one location the formation is typically less than 120 feet thick.
During the pedestrian survey, good exposures of the Otay Formation, specifically the gritstone
member, were observed in the east-central portion of the project site (Figure 3). In this location,
the sedimentary rocks are light brown, coarse-grained, poorly-sorted sandstone, characteristic of
the middle gritstone member of the Otay Formation (Figure 4). Based on the mapped geological
units and the pedestrian survey, it is likely that potentially fossiliferous deposits of the Otay
Formation underlie the majority of the project area, as well as portions of the proposed offsite
trails and utility corridors (Figure 1).
Paleontology:
Numerous fossil localities have been discovered in the gritstone member of the Otay Formation
in the Chula Vista and Otay Mesa areas of southwestern San Diego County. These localities have
produced well-preserved remains of a diverse assemblage of terrestrial vertebrates which
includes tortoises, lizards, snakes, birds, shrews, rodents, rabbits, dogs, foxes, cat-like nimravids,
rhinoceros, camels, mouse-deer, and oreodonts. Based on these fossil discoveries, the Otay
Formation is now considered to be the richest source of late Oligocene terrestrial vertebrates in
California (Deméré, 1988; Walsh and Deméré, 1991).
Site Specific Assessment:
Because of its paleontological richness, the Otay Formation is assigned a high paleontological
resource sensitivity.
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Figure 4. Artificial outcrop of the gritstone member of the Otay Formation along the aqueduct
alignment in the east central portion of Parcel B - Village 8 West. Overlying the Otay
Formation is a foot or more of topsoil and tilled ground surface.
Figure 5. Close-up of outcrop of the gritstone member of the Otay Formation, located in the artificial
outcrop shown in Figure 4.
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Quaternary alluvial and terrace deposits (Qoa)
Description:
Younger Quaternary alluvial and terrace deposits occur in the southeastern of the project site, as
well as portions of the proposed offsite trails and utility corridors (Figure 1). These sediments
consist of moderately- to poorly-consolidated deposits of “gravel, sand, silt, and clay” (Tan and
Kennedy, 2002) and were deposited by a Pleistocene-age proto-Otay River.
Paleontology:
No fossils are known from the Quaternary alluvial and terrace deposits in the immediate project
area. However, significant Pleistocene land mammal fossils have been found in similar deposits
throughout coastal San Diego County, including sites in the Sweetwater River Valley (Majors,
1993). It is likely that undisturbed portions of these potentially fossilferous deposits will yield at
least some significant Ice Age fossil specimens.
Site Specific Assessment:
Although disturbed at the surface of the project site by agricultural activities, the deeper,
undisturbed portions of Quaternary alluvial and terrace deposits are assigned a high
paleontological resource sensitivity.
Figure 6. View north from the southeastern portion of Parcel B - Village 8 West of outcrop of poorly
consolidated, coarse-grained Quaternary alluvial and terrace deposits.
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Holocene alluvial deposits (Qya)
Description:
Surface deposits within the project site consist of “unconsolidated to poorly consolidated silt,
clay, sand and gravel” and include “modern active sediments along small drainage channels”
(Tan and Kennedy, 2002). These deposits are Holocene in age (11,000 years ago to present; Tan
and Kennedy, 2002) and are associated with locally derived ephemeral stream drainages.
Paleontology:
The Holocene age of these deposits indicates they are too young to contain true fossil remains or
traces. Consequently, they do not represent significant paleontological resources.
Site Specific Assessment:
Holocene alluvial deposits are only mapped in the southern most region of the offsite
improvement area, in the Otay River Valley (Figure 1). Based on its post-Pleistocene age,
Holocene alluvial deposits are assigned a low paleontological resource sensitivity.
Results of Record Search
Eight previously recorded fossil collecting localities are documented in records housed at
SDNHM. All of these localities occur within a half mile or less of Parcel B - Village 8 West
(Appendix) and were discovered in sedimentary deposits of the Oligocene-age Otay Formation
during paleontological monitoring of construction projects.
The eight localities were all discovered within the Otay Formation, to the north and east of Parcel
B - Village 8 West. Two of the eight localities were collected from the fluvial gritstone member
of the Otay Formation during excavation for the SR 125 toll road. Fossils recovered from the
eight localities mentioned above included Hypertragulus sp. (extinct deer-like mammal),
Mesoreodon sp. and Sespia californica (extinct oreodonts), Hesperocyon sp. and Leptocyon sp.
(extinct members of the modern day dog family, Canidae), Archaeolagus sp. and Paleolagus sp.
(extinct rabbit relatives), Capacikala gradatus (extinct beaver relative), heliscomyid rodents,
squamates (e.g., lizards and snakes), and the very rare discovery of fossilized eggshell found
during grading at the Otay Ranch Village 7 project site to the north (SDSNH Localities 5679,
5697-5700, 5703, 5705, and 5946; Deméré, 2006; Korth, 1994; Appendix).
IMPACT ANALYSIS
INTRODUCTION
Direct impacts to paleontological resources occur when earthwork activities, such as mass
grading operations or trenching activities associated with the proposed off-site improvements, cut
into the geological deposits (formations) within which fossils are buried. These direct impacts
have the potential to destroy fossilized remains. Since fossils are the remains of prehistoric
animal and plant life, they are considered to be nonrenewable. Such impacts can be significant
and, under CEQA guidelines, require mitigation.
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Impacts to paleontological resources are typically rated from high to zero depending upon the
resource sensitivity of impacted formations.
High significance
Impacts to high sensitivity formations (Otay Formation and Quaternary alluvial and terrace
deposits). This includes excavation for proposed offsite improvements (e.g., storm drain and
sewer trenching) that will extend beyond the southern project boundary.
Moderate significance
Impacts to moderate sensitivity formations (none within the project site).
Low significance
Impacts to low sensitivity formations (Holocene alluvial deposits). This includes excavation for
proposed offsite improvements that will extend beyond the southern project boundary.
Zero significance
Impacts to formations with no fossil potential (Santiago Peak Volcanics).
SITE SPECIFIC IMPACTS
Santiago Peak Volcanics
Preliminary grading plans for the project site indicate that the metavolcanic bedrock of the
Santiago Peak Volcanics will be impacted during excavations in the southwestern portion of the
project site.
Otay Formation
The majority of the project site is underlain by the highly fossiliferous Otay Formation
Preliminary grading plans suggest that this sedimentary rock unit will be impacted by mass
grading activities, especially in the northeastern and southeastern portions. In addition,
construction of proposed offsite trails and utility corridors south of the project site has the
potential to also impact the Otay Formation (including rocks mapped as Tof by Tan and
Kennedy, 2002).
Quaternary alluvial and terrace deposits
Potentially fossilferous Quaternary alluvial and terrace deposits occur in the southeastern portion
of the project site. Preliminary grading plans suggest that these sedimentary deposits will be
impacted by mass grading activities. In addition, construction of proposed offsite trails and utility
corridors south of the project site has the potential to also impact the Quaternary alluvial and
terrace deposits.
Holocene alluvial deposits
Construction of proposed offsite facilities south of the project site are underlain by modern
alluvium.
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MITIGATION MEASURES
Prior to the issuance of grading permits, the Applicant shall provide written confirmation
to the City that a qualified paleontologist has been retained to carry out an appropriate
mitigation program. (A qualified paleontologist is defined as an individual with an M.S.
or Ph.D. in paleontology or geology who is familiar with paleontological procedures and
techniques). A pre grade meeting shall be held among the paleontologist and the grading
and excavation contractors.
A paleontological monitor shall be onsite at all times during the original cutting of
previously undisturbed sediments of highly sensitive geologic formations (i.e., Otay
Formation and Quaternary alluvial and terrace deposits) to inspect cuts for contained
fossils. (A paleontological monitor is defined as an individual who has experience in the
collection and salvage of fossil materials.) The paleontological monitor shall work under
the direction of a qualified paleontologist. The monitor shall be onsite on at least a half-
time basis during the original cutting of previously undisturbed sediments of moderately
sensitive geologic formations (e.g., unnamed river terrace deposits and the Mission
Valley Formation) to inspect cuts for contained fossils. However, neither of these rock
units have been mapped within the project site and are therefore not anticipated to be
impacted during construction.
o The monitor shall be onsite on at least a quarter-time basis during the original cutting
of previously undisturbed sediments of low sensitivity geologic formations (e.g.,
Lindavista Formation and Santiago Peak Volcanics [metasedimentary portion only] to
inspect cuts for contained fossils. However, these deposits have not been mapped
within the project site and are therefore not anticipated to be impacted during
construction. The monitor shall periodically (every several weeks) inspect original
cuts in deposits with an unknown resource sensitivity (i.e., Quaternary alluvium).
o In the event that fossils are discovered in unknown, low, or moderately sensitive
formations, the Applicant shall increase the per-day field monitoring time.
Conversely, if fossils are not discovered, the monitoring, at the discretion of the City's
Deputy City Manager/Development Services Director or its designee, shall be
reduced. A paleontological monitor is not needed during grading of rocks with no
resource sensitivity (i.e., Santiago Peak Volcanics, metavolcanic portion).
When fossils are discovered, the paleontologist (or paleontological monitor) shall recover
them. In most cases, this fossil salvage can be completed in a short period of time.
However, some fossil specimens (such as a complete whale skeleton) may require an
extended salvage time. In these instances, the paleontologist (or paleontological monitor)
shall be allowed to temporarily direct, divert, or halt grading to allow recovery of fossil
remains in a timely manner. Because of the potential for the recovery of small fossil
remains such as isolated mammal teeth, it may be necessary in certain instances and at the
discretion of the paleontological monitor to set up a screen-washing operation on the site.
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Prepared fossils along with copies of all pertinent field notes, photos, and maps shall be
deposited in a scientific institution with paleontological collections such as the San Diego
Natural History Museum. A final summary report shall be completed. This report shall
include discussions of the methods used, stratigraphy exposed, fossils collected, and
significance of recovered fossils.
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REFERENCES
Artim, E.R., and C.J. Pinckney. 1973. La Nacion fault system, San Diego, California. Geological
Society of America, Bulletin 84:1075-1080.
Deméré, T.A. 1988. Early Arikareean (late Oligocene) vertebrate fossils and biostratigraphic
correlations of the Otay Formation at EastLake, San Diego County, California. In, M.V.
Filewicz and R.L. Squires (eds.), Paleogene Stratigraphy, West Coast of North America.
Society of Economic Paleontologists and Mineralogists, Pacific Section 58:35-43.
Deméré, T.A. 2006. Paleontological Mitigation Report, Otay Ranch Village 7 Project, City of
Chula Vista, San Diego County, California: Prepared for The Otay Ranch Company, , p.
1-21.
Deméré, T.A., and S.L. Walsh. 1993. Paleontological Resources, County of San Diego: Prepared
for the Department of Public Works, County of San Diego, p. 1-60.
D'Vincent, S. 1967. Primitive Sequoia not previously identified. California Garden, August-
September 1967:14-15.
Eisentraut, P.J., and Cooper, J.D. 2002. Development of a model curation program for Orange
County's Archaeological and Paleontological Collections – Final Report: Submitted to the
County of Orange.
Fife, D.L., J.A. Minch, and P.J. Crampton. 1967. Late Jurassic age of the Santiago Peak
Volcanics, California. Geological Society of America, Bulletin 78:299-303.
Herzig, C.T., and D.J. Kimbrough. 1991. Early Cretaceous zircon ages prove a non-accretionary
origin for the Santiago Peak Volcanics, northern Santa Ana Mountains, California.
Geological Society of America, Cordilleran Section, Abstracts with Programs 23:35.
Jones, D.A., and R.H. Miller. 1982. Jurassic fossils from the Santiago Peak Volcanics, San Diego
County, California. In, P.L. Abbott (ed.), Geologic Studies in San Diego. San Diego
Association of Geologists, fieldtrip guidebook, pp. 93-103.
Kennedy, M.P., and S.S. Tan. 1977. Geology of National City, Imperial Beach, and Otay Mesa
quadrangle, southern San Diego metropolitan area, California Division of Mines and
Geology. Map Sheet 29, scale 1:24,000.
Korth, W. W. 1994. The Tertiary record of rodents in North America, New York Plenum Press,
p.319.
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Majors, C.P. 1993. Preliminary report on a late Pleistocene vertebrate assemblage from Bonita,
San Diego County, California. In, R.G. Dundas and D.J. Long (eds.), New Additions to
the Pleistocene Vertebrate Record of California. PaleoBios 15:63-77.
Pajak, A.F., Scott, E., and Bell, C. 1996. A review of the biostratigraphy of Pliocene and
Pleistocene sediments in the Elsinore Fault Zone, Riverside County, California:
PaleoBios v. 17(2-4), p. 28-49.
Tan, S.S, and M.P. Kennedy. 2002. Preliminary geologic map of the Otay Mesa 7.5’ Quadrangle,
San Diego County, California. California Geological Survey, scale 1:24,000.
Walawender, M.J. 2000. The Peninsular Ranges: A Geological Guide to San Diego’s Back
Country. Kendall/Hunt Publishing Company, Dubuque, Iowa.
Walsh, S.L., and T.A. Deméré. 1991. Age and stratigraphy of the Sweetwater and Otay
formations, San Diego County, California. In, P.L. Abbott and J.A. May (eds.), Eocene
Geologic History San Diego Region. Society of Economic Paleontologists and
Mineralogists, Pacific section, Vol. 68:131-148.
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APPENDIX