HomeMy WebLinkAboutGPA 09-01; ROBERTSON RANCH PA 22; NEGATIVE PALEONTOLOGICAL MONITORING AND MITIGATION REPORT LETTER; 2010-07-225rian F. Smith and Associates, Inc.
22 July 2010
Mr. Greg McDonnell
Brookfield Homes
12865 Pointe Del Mar, Suite 200
Del Mar, California 92014-3859
Arcl,aeology /.Biology/ Histor9 / ~/eontology / Afr Quality I Traffie I Acoustics
Subject: Negative paleontological monitoring and mitigation report, Robertson Ranch PA-22,
City of Carlsbad, San Diego County, California
Dear Mr. McDonnell:
The following letter repott summarizes our paleontological monitoring investigation conducted in
response to the City of Carlsbad's environmental mitigation requirements for grading and
earthmoving activities during constrnction of a parking area for the Robe1ison Ranch housing
development in the City of Carlsbad, San Diego County, California (Attachment 1 ). The project is
identified in the scope of the development as parking area P A-22 and is located on the south side
of Cannon Road midway between the intersections with Wind Trail Way and Hilltop Street.
Geologically, the small project area is mapped as being covered by Quaternary alluvium by Tan
and Kennedy (1996, California Division of Mines and Geology, DMG Open-File Report 96-02, pl.
1) but near the toe of a ridge identified as the second marine terrace (Qtz). On the digital geologic
map of the Oceanside 30' by 60' sheet, Kennedy and Tan (2005, California Geological Smvey,
Regional Geologic Map Series, 1: 100,000 scale, Map No. 2, sheet 1) map the previous Qt2 unit of
Tan and Kennedy (1996) as Quaternary older alluvium (Qoa). The sediments do not appear to be
marine in nature, and thus differ from the middle Pleistocene fossiliferous marine silts and fine-
grained sands that yielded the abundant marine inve1tebrate fossils in the project area north of
Cannon Road ( comparable to the BFSA collections made in mid March 2008). The Pleistocene
marine invertebrate fossils, however, are not included in the final paleontological mitigation rep01t
for the Robertson Ranch project that was prepared by the San Diego Natural History Museum in
September 2008.
Paleontological monitoring of grading and earthmoving activities on the site occurred
intermittently, as needed, between April 7, 2010 and June 10, 2010. Approximately half of the
site was a cut into an existing hillside, whereas the southern half of the site was overexcavated and
11010 Fbway Rood, SuitoA, Poway, CA 92.06+; Phone (858) 6l9-82JB or (951) 681-9950; fax (858) 679-9896; www.bfsa-ea.com
Business Office, 1+678 Ibex Court, San Diego, CA 9212.91 Phone (858) 48+-09151 fax (858) 48+-0988
built up with recompacted fill from the north-side excavation. The maximum amount of cut was
• approximately 14 feet, in the northeast part of the job site. Sediments consisted of a variety of
Quaternary alluvial and/or flu vial sandstones, with minor amounts of siltstone and clayey siltstone
lower in the main cut. Despite the potential for finding marine inve11ebrate fossils in the toe of the
mapped older alluvial sediments (Qoa of Tan and Kennedy, 2005), no fossils of any s011 were
observed in any of the graded exposures, side-slope cuts, or in the spoils generated by these
activities.
Based on this investigation, no significant paleontological resources are regarded as having been
lost or otherwise adversely affected by grading and earthmoving activities concomitant with
completion of the parking area (PA-22) for the Robertson Ranch housing development, and the
City of Carlsbad's mitigation requirements for preserving significant paleontological resources are
considered to have been satisfactorily completed.
If you have any questions, please feel free to contact us at our Poway address. Thank you for the
opportunity to have provided paleontological services for this project.
Sincerely,
George L. Kennedy, Ph.D. Gerald I. Shiller
• Senior Paleontologist California Professional Geologis
Attachments: Index map
I',,
Attachment 1
Project Location Map
The Robertson Ranch Parking Area (PA-22) Project
USGS San Luis Rey Quadrangle (7.5 minute series)
1000 2000 ft