SITE INFORMATION AND CORRESPONDENCE

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5.8:PALEONTOLOGICAL RESOURCES and Sierra Nevada-derived sediments were deposited in the basin east of the valley axis (Wahrhaftig and Birman,1965). While the sedimentary sequence of the Great Valley is commonly thought to be relatively continuous,this is not necessarily the case for the project area. Glacioeustatic lowering of sea level by as much as 400 feet during Quaternary glacial advances over the last approximately 700,000 years (e.g., Bloom, 1983) caused stream entrenchment and hydrographic isolation of the current floodplains (Shlemon,1971). Concurrent with this entrenchment was the westward expansion of the Sierran alluvial fans,and concurrent western retreat of delta systems. A general lack of glacial-age sedimentation on the interglacial floodplains was the result (ibid.). Conversely, during interglaciations such as the current Holocene (the last 10,000 years),sea-level rises to near present elevations,and the fan-delta system extend farther to the east,inland. Fluvial sedimentation in the project area occurred during overbank floods and from simple river meander after sea level had reached near its present elevation, and before the historic channelization of the delta (Lettis and Unruh,1991). Marchand and Atwater (1979) mapped the historic limit of the autumnal high-tides of the delta only about 0.7 mile west of the project area. 5.8.2.2 Resource Inventory Methods To develop a baseline paleontological resource inventory of the project area and surrounding lands,and to assess the potential paleontological productivity of the stratigraphic units that may be present,published as well as available unpublished geological and paleontological literature was reviewed. Sources included geological maps, satellite and aerial photography, and technical and scientific reports. For LEC,an updated paleontological resources records review was conducted for the project using the on-line database maintained by the University of California Museum of Paleontology at Berkeley (UCMP). Field reconnaissance of the project area and off-site lateral was conducted on June 3,2008 by the project paleontological resources specialist,Dr.W. Geoffrey Spaulding. 5.8.2.3 Resource Inventory Results 5.8.2.3.1 Geological Units in the Vicinity Below a layer of as much as 10 feet of Holocene eolian deposits and alluvium,Late Quaternary sediments beneath the project area are chiefly of fluvial origin,attributable to the Mokelumne River,and perhaps the San Joaquin as well (Marchand and Atwater, 1979; Kleinfelder,1993). As appropriate to a site near the margin of the great Sacramento-San Joaquin Delta,the lay of the land is nearly flat with the surface sloping very gently at less than a one percent grade to the west. Local drainage is currently directed by a complex series of canals and drains that usually terminate in one of the sloughs of the delta system. The elevation of the site varies from about 5 to 6 feet amsl at the plant area. The local area is underlain by a complex series of sedimentary and volcanic rocks ranging in age from Jurassic to Tertiary. A thick sequence of fluvial deposits and some estuarine clays and silts comprises the shallower sedimentary package of the Great Valley province in the Lodi area. These sedimentary deposits consist of interbedded sand, silt,and clay. A brief description of the stratigraphy of the project area is presented here. The most detailed mapping of the surficial geology of the project area was completed by Marchand and Atwater (1979) and they recognized five mapping units of the Modesto 5.8-2 SAC/371322/082340008(LEC_5.8_PALEORES.DOC)