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Paleontological Resource Inventory and Assessment by Rock Unit
<br /> Dune Sand
<br /> By definition,to be considered a fossil, a specimen must be more than 10,000 years old. Because the Dune Sands
<br /> are of Holocene age and are therefore 10,000 years old or younger, any specimens recovered from this formation
<br /> would not be considered a fossil.
<br /> Modesto Formation
<br /> Vertebrate mammalian fossils have proved helpful in determining the relative age of alluvial fan sedimentary
<br /> deposits(Albright 2000,Louderback 1951, Savage 1951). Mammalian inhabitants of the Pleistocene alluvial fan
<br /> and floodplain included mammoths,horses,mastodons, camels, ground sloths, and pronghorns.
<br /> The Pleistocene epoch,known as the"great ice age,"began approximately 1.8 million years ago. Surveys of late
<br /> Cenozoic land mammal fossils in northern California have been provided by Hay(1927), Lundelius et al. (1983),
<br /> Jefferson(1991a, 1991b), Savage(1951), and Stirton(1939). On the basis of his survey of vertebrate fauna from
<br /> the nonmarine late Cenozoic deposits of the San Francisco Bay region, Savage(195 1)concluded that two major
<br /> divisions of Pleistocene-age fossils could be recognized: the Irvingtonian(older Pleistocene fauna)and the
<br /> Rancholabrean(younger Pleistocene and Holocene fauna). These two divisions of Quaternary Cenozoic
<br /> vertebrate fossils are widely recognized today in the field of paleontology. The age of the later Pleistocene,
<br /> Rancholabrean fauna was based on the presence of bison and on the presence of many mammalian species that are
<br /> inhabitants of the same area today. In addition to bison, larger land mammals identified as part of the
<br /> Rancholabrean fauna include mammoths,mastodons, camels,horses, and ground sloths.
<br /> Remains of land mammals have been found in the project region at various localities in alluvial deposits referable
<br /> to the Modesto Formation. Jefferson(1991a, 1991b)compiled a database of California late Pleistocene vertebrate
<br /> fossils from published records,technical reports,unpublished manuscripts, information from colleagues, and
<br /> inspection of museum paleontological collections at more than 40 public and private institutions. He listed a
<br /> number of sites in San Joaquin County that have yielded Rancholabrean vertebrate fossils that could be referable
<br /> to the Modesto Formation. Jefferson's information corresponds with the records in the UCMP database.
<br /> The closest identified vertebrate fossils to the project area are located approximately 2 miles northeast of the
<br /> proposed north Manteca trunk sewer branch on Union Road, at Littlejohns Creek(UCMP V-5107). This site
<br /> yielded seven specimens from Rancholabrean-age Columbian mammoth,horse, and an unidentified carnivore
<br /> from sediments of the Modesto Formation. Approximately 3 miles west of the WQCF site,remains of a
<br /> Pleistocene mammal were encountered in sediments of the Modesto Formation during construction activities
<br /> associated with the River Islands project.Approximately 8 miles north of the WQCF site, in Stockton,locality
<br /> V-4822 yielded a Rancholabrean-age horse specimen. Hay(1927)reported remains of camel,horse, and
<br /> mammoth at another site in Stockton.
<br /> UCMP localities V-66150,V-3315,V-4809,V-4810,V-4808,V4819, and V-4807, along the Delta Mendota
<br /> Canal west of Tracy(approximately 20 miles southwest of the project area),yielded numerous specimens from
<br /> bison,mammoth, ground sloth,horse, and gopher. In the same area,the Wagner's Aqueduct site,V-70122,
<br /> yielded three specimens from the class Osteichthyes (bony fishes). Localities V-4804 and V-4867 from the
<br /> Reiche Gravel Pit,west of the Delta Mendota Canal,yielded three specimens of horse and mammoth remains.
<br /> Locality V-66150 at the Tracy Gravel Pit yielded a specimen of Jefferson's ground sloth,while locality V-3315 at
<br /> the Hetch Hetchy Tunnel yielded remains from a Rancholabrean-age camel. Finally, a site along Cometa Road,
<br /> approximately 20 miles east of the project area(V-5039),yielded two Pleistocene horse specimens.
<br /> Specimens from sediments referable to the Modesto Formation have been reported at other locations throughout
<br /> the Central Valley(UCMP 2004). The Tranquility site in Fresno County(UCMP V-4401), for example,has
<br /> yielded more than 130 Rancholabrean-age fossils of fish,turtles, snakes,birds,moles, gophers,mice,wood rats,
<br /> EDAW Manteca WQCF and Collection System Master Plans EIR
<br /> Paleontological Resources 4.8-4 City of Manteca
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