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5.8:PALEONTOLOGICAL RESOURCES TABLE 5.8-1 Paleontological Sensitivity Ratings Employed Definition High Assigned to geological formations known to contain paleontological resources that include rare,well-preserved, and/or fossil materials important to on-going paleoclimatic, paleobiological and/or evolutionary studies.They have the potential to produce, or have produced vertebrate remains that are the particular research focus of many paleontologists, and can represent important educational resources as well. Moderate Stratigraphic units that have yielded fossils that are moderately well-preserved, are common elsewhere, and/or that are stratigraphically long-ranging would be assigned a moderate rating.This evaluation can also be applied to strata that have an unproven but strong potential to yield fossil remains based on its stratigraphy and/or geomorphologic setting. Low Sediment that is relatively recent, or that represents a high-energy subaerial depositional environment where fossils are unlikely to be preserved.A low abundance of invertebrate fossil remains, or reworked marine shell from other units, can occur but the paleontological sensitivity would remain low due to their lack of potential to serve as significant scientific or educational purposes. Marginal and Stratigraphic units with marginal potential include pyroclastic flows and soils that might Zero preserve traces or casts of plants or animals. Most igneous rocks, however, have zero paleontological potential. Other stratigraphic units deposited subaerially in a high energy environment(such as alluvium)may also be assigned a marginal or zero sensitivity rating. Manmade fill is also considered to possess zero(no)paleontological potential. As noted above,within one mile of the project area there is a limited suite of geological units,restricted to different facies of the Modesto Formation and overlying disturbed sediment,and no paleontological localities have been recorded within a mile of the site. No paleontological localities are known from the Modesto Formation in San Joaquin County; although some vertebrate localities from undifferentiated Quaternary sediments could in fact be in the Modesto Formation. Nevertheless,based on the absence of fossils records from this unit,the Modesto Formation in this area is assigned low paleontological sensitivity. The low paleontological sensitivity of the Modesto Formation in this area is also supported by the recent geomorphic history of the fan-delta region. Due to drastically lower sea level during the last glacial age (Bloom,1983),sediments did not begin aggrading at present elevations until after about 10,000 B.P. (Schlemon,1976),while the end of the Rancholabrean Land Mammal Age can now be rather precisely dated at about 10,900 B.P. (Martin,2006). Therefore,megafaunal remains of the Rancholabrean would not be expected in the sediments mapped as Modesto Formation in the project area. Further demonstrating the low paleontological sensitivity of the Modesto Formation are excavations in sediments mapped as the Modesto within 20 feet of river level on the south bank of the San Joaquin River, about 21 miles west-southwest of the LEC near Antioch. These have yielded no scientifically significant paleontological materials despite more than three years of episodic monitoring(CH2M HILL,n.d.). Approximately 50 miles to the southeast,near Turlock,in Stanislaus County,recent investigations found the Modesto Formation to be devoid of fossils. The underlying upper Riverbank Formation did yield vertebrate fossils (Spaulding and Naidu,2006). The Riverbank Formation has not been 5.8-4 SAC/371322/082340008(LEC_5.8_PALEORES.DOC)