HomeMy WebLinkAboutCT 2018-0002; AVIARA APARTMENTS; PALEONTOLOGICAL MITIGATION; 2023-06-29
29 June 2023
Catherine Wright
HELIX Environmental Planning, Inc.
7578 El Cajon Boulevard
La Mesa, California 91942
RE: Paleontological Mitigation – Aviara Apartments Development
Dear Ms. Wright:
This letter report presents the results of the paleontological mitigation program conducted
during earthwork operations for the Aviara Apartments Development project (Project), located in the
west central portion of the City of Carlsbad, San Diego County, California (Figure 1). The approximately
9.5-acre Project site consists of a parcel that spans Aviara Parkway. The western lot is bordered to the
east by Aviara Parkway, to the south and west by undeveloped land, and to the north by Encinas Creek
and existing commercial development. The eastern lot is bordered to the west by Aviara Parkway, to the
south and east by Laurel Tree Lane, and to the north by Encinas Creek. Proposed work at the site will
include construction of a new multi-family apartment community, to include a total of 329 residential
apartment units and associated on-site leasing office, recreational amenities, and parking.
Project Background
Published geological mapping (Kennedy and Tan, 2007; Figure 1) covering the Project area
indicates that the Project site is underlain by late Pleistocene to Holocene-age (less than 11,700 years
old) young alluvial flood plain deposits and the middle Eocene-age (approximately 49 to 40 million years
old) Santiago Formation. According to the site-specific geotechnical investigation report, undocumented
artificial fill is present across the Project site, extending to depths of 3 to 7 feet below ground surface
(bgs; GeoSoils, 2019). The Santiago Formation is assigned a high paleontological sensitivity in San Diego
County (Deméré and Walsh, 1993), and it was therefore determined that a paleontological mitigation
program should be implemented in order to reduce any potential impacts to paleontological resources
to less than significant levels, as outlined in Mitigation Measure (MM) GEO-1 in the Mitigation
Monitoring and Reporting Program for the Aviara Apartments Final Environmental Impact Report. This
final paleontological mitigation report completes the paleontological mitigation program for the Project.
Methods
Excavation operations at the Project site were intermittently monitored for paleontological
resources between February 13 and April 20, 2023. Monitoring was carried out in accordance with all
applicable city, county, and state guidelines and consisted of on-site inspection of areas of active
earthwork for unearthed fossil remains, including examination of temporary exposures and recently
excavated spoils piles (Figure 2). In addition to inspecting earthwork for unearthed fossil remains, the
paleontological monitors recorded information concerning the lithology, stratigraphy, and lateral extent
of exposed strata. Such information is essential for providing geologic context for any discovered fossils.
Aviara Apartments Development—Paleontological Mitigation Report 2
Aviara Apartments Development—Paleontological Mitigation Report 3
Figure 2. Typical monitoring conditions at the Project site, showing mass grading (left) and later subgrade
excavations (right) impacting white sandstone deposits of the Santiago Formation. Photos taken by R.J.
Grundler on 17 March 2023 (left) and by J.K. Shelmire on 20 April 2023 (right).
Safety procedures followed by field personnel included wearing appropriate clothing (e.g., high-
visibility vests, hard hats, steel toe boots, safety glasses), carrying large handheld orange flags, securing
the attention of equipment operators before approaching an active cut, using caution when driving near
the Project site, and attendance at safety meetings. Monitoring did not interfere with or delay
construction operations.
Results
Stratigraphy – Project-related excavations exposed approximately six vertical feet of strata of
the Santiago Formation, which was exposed between approximately 72 and 78 feet above sea level (asl).
The observed strata consisted of white, micaceous, massive to moderately bioturbated, moderately
indurated, very fine-grained sandstone. Along the north wall cut, the Santiago Formation was overlain
by approximately four feet of alluvial deposits, which pinched out to the west. The alluvial deposits
consisted of tan, massive, moderately indurated, medium- to fine-grained sandstone. Farther west along
the north wall cut, the alluvial deposits measured one foot thick and consisted of light tan, laminated,
moderately indurated, fine-grained sandstone containing gray siltstone clasts along the lower contact. A
veneer of artificial fill that measured approximately two feet thick was present across the surface of the
Project site.
Fossils – Blocks of sandstone containing several infilled burrows measuring between 0.5 and
1.5 cm in diameter were observed in a vertical cut exposing the Santiago Formation at approximately 77
feet asl in the central portion of the western lot (Figure 3). The burrows were salvaged from the Project
site and transported to the Museum for further inspection. The specimens were ultimately too poorly
preserved to be diagnostic of a particular ichnotaxon and were, therefore, discarded. No other fossils
were observed during paleontological monitoring of construction earthwork.
Aviara Apartments Development—Paleontological Mitigation Report 4
Figure 3. View of a sandstone block from the Santiago Formation containing several infilled burrows, indicated
by arrows. The ichnofossils were salvaged from the Project site, but were ultimately discarded due to
their poor preservation. Photo taken by R.J. Grundler on 9 March 2023.
Discussion
Paleontological mitigation is not an exact discipline and, on occasion, no scientifically significant
fossil remains are unearthed during the course of a mitigation program. However, monitoring (i.e.,
looking for fossil remains) has to proceed since fossils could be discovered at almost any time. In the
event that no fossils are unearthed, the other standard tasks of a mitigation program are not performed.
The lack of discovery of scientifically significant fossils within the Project site may be attributable to
chemical leaching of once-present fossil remains by groundwater, syndepositional destruction of
delicate specimens, and/or an original paucity of paleontological resources.
It is noteworthy that elsewhere in San Diego County, including in the vicinity of the Project site,
the Santiago Formation has produced scientifically significant collections of both marine and estuarine
fossils (e.g., mollusks, arthropods, sharks, rays, bony fishes), as well as terrestrial fossils (e.g., turtles,
snakes, lizards, crocodiles, birds, mammals) (e.g., Bukry, 1991; Deméré and Boettcher, 1985; Wilson,
1972; unpublished SDNHM paleontological collections data). The terrestrial mammalian fossils
recovered from the Santiago Formation are particularly significant, and include remains of opossums,
insectivores, primates, rodents, carnivores, brontotheres, tapirs, protoreodonts, and other early
Aviara Apartments Development—Paleontological Mitigation Report 5
artiodactyls (e.g., Colbert, 2006; Golz, 1976; Golz and Lillegraven, 1977; Ludtke and Prothero, 2004;
Mihlbacher and Deméré, 2009; Theodor, 1999; Tomiya, 2013; Walsh, 1991, 1996; Wesley and Flynn,
2003; Zack et al., 2022). These scientifically significant finds demonstrate the importance of
paleontological mitigation programs and the high paleontological sensitivity of the Santiago Formation.
Department of PaleoServices personnel involved in this mitigation program included
Paleontological Monitors Ross J. Grundler, Bradford O. Riney, and Jesse K. Shelmire; Field Manager
Rodney M. Hubscher; Assistant Report Writer Kirstin L. Mueller; Paleontological Report Writer & GIS
Specialist Katie M. McComas; and Principal Paleontologist Thomas A. Deméré.
If you have any questions concerning these findings, please feel free to contact me at
kmueller@sdnhm.org.
Sincerely,
Kirstin Mueller
Assistant Report Writer
San Diego Natural History Museum
Literature Cited
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Lagoon, San Diego County. In, P.L. Abbott and J.A. May (eds.), Eocene Geologic History, San
Diego Region. Society of Economic Paleontologists and Mineralogists, Pacific Section 68: 189-
194.
Colbert, M.W. 2006 Hesperaletes (Mammalia, Perissodactyla), a new tapiroid from the middle Eocene of
southern California. Journal of Vertebrate Paleontology 26: 697-711.
Deméré, T.A., and R.S. Boettcher. 1985. Paleontology and biostratigraphy of middle Eocene nearshore
marine sedimentary rocks, Leucadia, San Diego County, California. In, P.L. Abbott (ed.), On the
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of Geologists, fieldtrip guidebook, pp. 49-53.
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technical report prepared for the San Diego County Department of Public Works: 1–68.
GeoSoils, Inc. 2019. Revised preliminary geotechnical evaluation, 9.2 acres, APN 212-040-56-00, Laurel
Tree Lane at Aviara Parkway, Carlsbad, San Diego County, California. Unpublished technical
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Golz, D.J. 1976. Eocene Artiodactyla of southern California. Natural History Museum of Los Angeles
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Aviara Apartments Development—Paleontological Mitigation Report 6
Golz, D.J., and J.A. Lillegraven. 1977. Summary of known occurrences of terrestrial vertebrates from
Eocene strata of southern California. University of Wyoming, Contributions to Geology 15:43-65.
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