Paleontological Resource Assessment Garrett-Menifee Project City of Menifee Riverside County, California September 5, 2018 (Revised February 1, 2019) Prepared for: The Garrett Group Two Betterworld Circle, Suite 200 Temecula, CA 92590 Prepared by: Department of PaleoServices San Diego Natural History Museum 1788 El Prado San Diego, California 92101 Katie M. McComas, M.S., Paleontological Report Writer Thomas A. Deméré, Ph.D., Principal Paleontologist Executive Summary This paleontological resource assessment was prepared for the Garrett-Menifee Project (Project) (Tentative Tract No. 33419) in the City of Menifee, Riverside County, California. The purpose of this report is to identify and summarize paleontological resources that occur within the vicinity of the Project site, identify Project elements (if any) that may negatively impact paleontological resources, and provide recommendations to reduce any potential negative impacts to less than significant levels, if necessary. The report includes the results of institutional records searches conducted at the Western Science Center (WSC) and San Diego Natural History Museum (SDNHM). The approximately 47 acre Project site is located in the northern portion of the City of Menifee, and is bordered to the north by McLaughlin Road, to the west by Evans Road, to the south by Rouse Road, and to the east by Barnett Road. Proposed work at the site will include construction of 174 single-family residential buildings, a 1.2 acre community park, a 0.8 acre water quality basin, and attendant access roadways and wet and dry underground utilities. Specific details on planned earthwork at the site are undefined, but site-wide remedial over-excavation and recompaction earthwork is anticipated. Published geologic mapping for the Project site indicates the site is underlain by Quaternary old alluvial- fan deposits (Qof). The alluvial fan deposits are considered to be middle to late Pleistocene in age (~800,000 to 11,000 years old) at the surface. Site-specific geotechnical investigations documented the occurrence of a thin veneer (~2–3 feet) of surficial deposits of Holocene-age colluvium over the majority of the Project site. No recorded fossil collection localities at WSC or SDNHM are known from within a 1-mile radius of the Project site. However, significant fossils have been discovered less than 10 miles to the southeast in similar Pleistocene-age alluvial fan deposits exposed during construction of the Diamond Valley Lake project. Recovered fossils consist of large-bodied “Ice Age” mammals (e.g., ground sloth, weasel, skunk, badger, wolf, sabertoothed cat, American lion, puma, peccary, camel, pronghorn antelope, deer, bison, mastodon, and mammoth). Following the paleontological guidelines described in the City of Menifee’s General Plan DEIR, a high paleontological sensitivity is assigned to Quaternary old alluvial-fan deposits underlying the entire Project site. This assignment is supported by the occurrence of known fossils in the City of Menifee, and elsewhere in western Riverside County. Construction of the proposed Project has the potential to impact paleontological resources during earthwork within Quaternary old alluvial-fan deposits. Thus, implementation of a paleontological mitigation program centered around paleontological monitoring is recommended, as outlined in the provided Mitigation Measures 1–7. Implementation of the paleontological mitigation program will reduce any Project-related impacts to paleontological resources to a level that is less than significant. Garrett-Menifee Project - Paleontological Resource Assessment i Contents Executive Summary ............................................................................................................................ i 1.0 Introduction .................................................................................................................................1 1.1 Project Description and Scope of Work ........................................................................................ 1 1.2 Definition of Paleontological Resources ....................................................................................... 1 1.3 Regulatory Framework ................................................................................................................. 3 1.3.1 Local ...................................................................................................................................... 3 2.0 Methods ......................................................................................................................................3 2.1 Paleontological Records Search and Literature Review ............................................................... 3 2.2 Paleontological Resource Assessment Criteria ............................................................................. 3 2.2.1 High Potential/Sensitivity ...................................................................................................... 4 2.2.2 Low Potential/Sensitivity ....................................................................................................... 4 2.2.3 Undetermined Potential/Sensitivity ..................................................................................... 4 2.3 Paleontological Impact Analysis ................................................................................................... 4 3.0 Existing Conditions: Geologic Setting .............................................................................................5 4.0 Results .........................................................................................................................................5 4.1 Results of the Records Searches and Literature Review .............................................................. 5 4.1.1 Project Paleontology ............................................................................................................. 5 4.1.2 Project Geology ..................................................................................................................... 5 4.2 Results of Paleontological Sensitivity Analysis ............................................................................. 8 4.3 Results of Paleontological Impact Analysis................................................................................... 8 5.0 Recommendations & Conclusions .................................................................................................8 5.1 Mitigation Measures ..................................................................................................................... 8 6.0 References ................................................................................................................................. 10 Appendix ......................................................................................................................................... 11 Garrett-Menifee Project - Paleontological Resource Assessment ii 1.0 Introduction 1.1 Project Description and Scope of Work This technical report provides an assessment of paleontological resources at the Garrett-Menifee Project (Project) site (Tentative Tract No. 33419) in the City of Menifee, Riverside County, California (Figure 1). The approximately 47 acre Project site is located in the northern portion of the City of Menifee, and is bordered to the north by McLaughlin Road, to the west by Evans Road, to the south by Rouse Road, and to the east by Barnett Road. Proposed work at the site will include construction of 174 single-family residential buildings, a 1.2 acre community park, a 0.8 acre water quality basin, and attendant access roadways and wet and dry underground utilities. Specific details on planned earthwork at the site are undefined, but site-wide remedial over-excavation earthwork is anticipated. Because the Project site occurs in an area underlain by native sedimentary deposits, a paleontological resource assessment was conducted in order to evaluate whether the proposed Project has the potential to negatively impact paleontological resources. This assessment report is intended to summarize existing paleontological resource data at the Project site, discuss the significance of these resources, evaluate possible Project related impacts to paleontological resources, and provide recommendations to reduce any impacts to paleontological resources to less than significant levels (if necessary). The assessment also presents the results of institutional records searches of the paleontological collections at the Western Science Center (WSC) and San Diego Natural History Museum (SDNHM). This report was prepared by Katie M. McComas and Thomas A. Deméré of the Department of PaleoServices, SDNHM. 1.2 Definition of Paleontological Resources As defined here, paleontological resources (i.e., fossils) are the buried remains and/or traces of prehistoric organisms (i.e., animals, plants, and microbes). Body fossils such as bones, teeth, shells, leaves, and wood, as well as trace fossils such as tracks, trails, burrows, and footprints, are found in the geologic deposits within which they were originally buried. The primary factor determining whether an object is a fossil or not isn’t how the organic remain or trace is preserved (e.g., “petrified”), but rather the age of the organic remain or trace. Although typically it is assumed that fossils must be older than ~10,000 years (i.e., the generally accepted end of the last glacial period of the Pleistocene Epoch), organic remains of early