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MainPlace Mall Transformation Project 12126.001 <br />iXlxcl=N 1161c] 19IN =11 i I101"M 01U1&111-1-111 N yeCd ZKKS] 01UJ 111IQ01 V <br />2.1 Geologic Setting <br />The site is located in the Los Angeles Basin, which is a large structural <br />depression within the northern portion of the Peninsular Ranges geomorphic <br />province of Southern California. The Peninsular Ranges province extends 900 <br />miles southward from the Los Angeles basin to the tip of Baja California (Yerkes, <br />et al., 1965) and is characterized by elongated, northwest -trending, mountain <br />ridges separated by straight -sided, sediment -floored valleys. However, the most <br />dominant structural features of the province are the northwest -trending fault <br />zones, most of which either die out, merge with, or are terminated by the steep <br />reverse faults at the southern margin of the Transverse Ranges province. These <br />fault zones separate large elongated blocks, each standing at different structural <br />elevations. There are no known active faults known to cross the project site and <br />the site is not mapped within an Alquist-Priolo Earthquake Fault Zone (Bryant <br />and Hart, 2007). The closest active fault to the site (5.8 miles away) is the San <br />Joaquin Hills blind thrust fault. The San Joaquin Hills are a surficial expression <br />of a faulted anticline associated with movement on the underlying San Joaquin <br />Hills blind thrust fault. <br />The site is located approximately 0.8 mile southeast of the Santa Ana River and <br />approximately 400 feet north of Santiago Creek. The near -surface native soils at <br />the site are Quaternary -age, non -marine young alluvial fan deposits comprised of <br />varying proportions of sand, gravel, silt, and clay deposited by the Santa Ana <br />River and its tributaries (Morton and Miller, 2006). A map showing the mapped <br />geologic units in the vicinity of the project site is presented as Figure 3, Regional <br />Geology Map. <br />2.2 Local Geologic Units and Subsurface Conditions <br />Presented below are summaries of the geologic units encountered in the <br />exploratory borings completed at the site by Leighton (Leighton 2019) and others <br />(See Section 1.3). <br />2.2.1 Undocumented Artificial Fill: (Afu) <br />Fill materials encountered by Irvine Soils Engineering Inc. (ISE, 1985a) <br />throughout the site ranged in thickness up to a maximum of approximately <br />8 feet. The fill soils encountered by ISE generally consisted of a medium <br />3 9 <br />Leighton <br />