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<br />9/22/19 «P:\WKE1702\Paleo\September 2018 Submittal\Fairview Street Improvements_Draft Paleo Memo 090718.docx» 4
<br />deposits since the Late Cretaceous (approximately 100.5 Ma) (Yerkes et al., 1965). Over millions of
<br />years, the Basin has experienced episodes of subsidence, deposition, uplift, erosion, and faulting, all
<br />of which have resulted in very complex geology and a very productive oil industry (Bilodeau et al.,
<br />2007; Yerkes et al., 1965). The surface of the basin slopes gently southwestward toward the ocean,
<br />interrupted in various places by low hills and traversed by several large rivers (Sharp, 1976; Yerkes et
<br />al., 1965), including the Los Angeles River, the Rio Hondo, the San Gabriel River, and the Santa Ana
<br />River.
<br />Geologic mapping by Morton and Miller (2006) shows that the Project Area contains Very Young
<br />Wash Deposits and Young Alluvial Fan Deposits (see Figure 2, Geologic Map, provided in Attachment
<br />B). In addition, because the Project Area has been previously developed, some amount of Artificial
<br />Fill is likely present at the surface above the geologic unit mapped by Morton and Miller (2006).
<br />Ages for the geologic epochs and subdivisions are based on the International Chronostratigraphic
<br />Chart prepared by the International Commission on Stratigraphy (ICS, 2017) and Walker et al.
<br />(2012).
<br />Artificial Fill
<br />Artificial Fill consists of sediments that have been removed from one location and transported to
<br />another location by human activity, rather than by natural means. The transportation distance can
<br />vary from a few feet to many miles, and composition is dependent on the source and purpose.
<br />While Artificial Fill may contain fossils, these fossils have been removed from their original location
<br />and are thus out of stratigraphic context. Therefore, they are not considered important for scientific
<br />study. As such, Artificial Fill has no paleontological sensitivity.
<br />Very Young Wash Deposits
<br />The Very Young Wash Deposits are late Holocene in age (less than 4,200 years ago; Walker et al.,
<br />2012) and consist of unconsolidated sand and gravel in active washes, channels on active alluvial
<br />fans, and ephemeral streams (Morton and Miller, 2006). These deposits accumulated along river
<br />and stream channels as floods and debris flows carried sediment down from higher elevations. The
<br />size, color, and types of clasts in these deposits are dependent on the local bedrock from which they
<br />were derived, with boulder‐size clasts more common closer to the mountains and in areas prone to
<br />flash floods (Morton and Miller, 2006). These deposits are mapped along the Santa Ana River
<br />channel in the Project Area.
<br />Although Holocene deposits can contain remains of plants and animals, only those from the middle
<br />to early Holocene (4,200 to 11,700 years ago; Walker et al., 2012) are considered scientifically
<br />important (SVP, 2010). Older deposits that may contain scientifically important fossils may be
<br />encountered at undetermined depths below these late Holocene deposits. Therefore, the Very
<br />Young Wash Deposits are considered to have low paleontological sensitivity.
<br />Young Alluvial Fan Deposits
<br />Young Alluvial Fan Deposits, which are Holocene to late Pleistocene in age (less than 126,000 years
<br />ago; ICS, 2017), consist of unconsolidated gravel, sand, and silt with occasional cobbles and boulders
<br />near mountain fronts (Morton and Miller, 2006). These sediments were deposited by flooding
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