75B - PH ADOPT RESO FOR PR NO 15-6827

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L S A FAIRVIEW BRIDGE REPLACEMENT AND STREET IMPROVEMENTS (9TH STREET TO 16TH STREET( PROJECT INITIAL STUDY/MITIGATED NEGATIVE DECLARATION SANTA ANAL CALIFORNIA MAY 2020 The Project area is relatively flat and situated at an elevation of about 100 ft. In the natural regime, the Project area is within the Santa Ana River flood plain, and the portion of the river through the Project area is confined to a concrete -lined channel. Exploratory boreholes, drilled in the years 2003 and 2004 in the Project area, show that the area i underlain by nonindurated alluvial sediments ranging from clay to sand to gravel. The soils are Holocene -age flood -plain sediments of the Santa Ana River. Generally, the soils within the Project area consist of alternating, interbedded layers of sand with varying fines content, lean clay with varying amounts of sand, and few silt layers. The deeper sand layers include trace to moderate amounts of fine to coarse gravel. 3.7.1.2 Paleontological Resources Project plans, geologic maps of the Project area, and relevant geological and paleontological literature were reviewed to determine which geologic units are present in the Project area and whether fossils have been recovered in the Project area or from those or similar geologic units elsewhere in the region. In addition, a search for known fossil localities was conducted through the Natural History Museum of Los Angeles County (LRCM) to determine the status and extent of previously recorded paleontological resources within and surrounding the Project area. Afield survey of the Project area was also conducted to note the sediments at the surface; relocate any known paleontological localities, if present; and identify any unrecorded paleontological resources exposed on the surface of a Project area. Results of the literature review indicate that the Project area is located at the northern end of the Peninsular Ranges Geomorphic Province, a 900 mi long northwest -southeast -trending structural block that extends from the Transverse Ranges in the north to the tip of Baja California in the south. Within this larger region, the Project is located in the Los Angeles Basin, a broad alluvial lowland bounded to the north and east by the San Gabriel and Santa Ana Mountains, respectively, and by the Pacific Ocean to the southwest. Geologic mapping by Morton and Miller shows that the Project area contains Very Young Wash Deposits and Young Alluvial Fan Deposits. In addition, because the Project area has been previously developed, some amount of Artificial Fill is likely present at the surface above the geologic unit mapped by Morton and Miller. Ages for the geologic epochs and subdivisions are based on the International Chronostratigraphic Chart prepared by the International Commission on Stratigraphy and Walker et al. Artificial Fill consists of sediments that have been removed from one location and transported to another location by human activity, rather than by natural means. The transportation distance can vary from a few feet to many miles, and composition is dependent on the source and purpose. While Artificial Fill may contain fossils, these fossils have been removed from their original location and are thus out of stratigraphic context. Therefore, they are not considered important for scientific study. As such, Artificial Fill has no paleontological sensitivity. The Very Young Wash Deposits are late Holocene in age (less than 4,200 years ago) and consist of unconsolidated sand and gravel in active washes, channels on active alluvial fans, and ephemeral 3-38 7 584,2ND\Final ISMND\Fairview Street Bridge Final ISMND.doC. (05/26/20)