SITE INFORMATION AND CORRESPONDENCE_FILE 1

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highway embankments. Broad, shallow depressions, many of which are defined by the above structures, are common in the area. 3.2 Geology The Central Valley of California is a lowland between two moun- tain ranges, the Sierra Nevada on the east, and the Coast Range on the west. This Valley has existed as a structural trough, receiving sediments from the adjacent mountains, since pre - Cretaceous times. Through much of its history, the Central Valley has been an arm of the sea, and the materials transported into it were deposited under marine conditions. In late Tertiary times, general uplift of the region resulted in the retreat of the sea, and the onset of continental deposition. This uplift was accompanied by volcanism to the east which produced volcanic materials subsequently eroded and deposited in the Valley as the Mehrten and Valley Springs Formations. Contin- ual uplift during the Pleistocene resulted in the formation of the Sierra Nevada mountains as they are known today. This uplift accelerated erosion, providing more material for deposition in the Valley. Later, large lakes formed on the west side of the Valley, resulting in excessive deposits of clay, now termed the Corcorran Clay. Pleistocene and recent times have been characterized by the deposition of relatively coarse sedimentary materials (silt, sand, and gravel) in alluvial fans along the Valley margins. In the lower parts of the Central Valley, particularly along the San Joaquin River, there are finer floodplain deposits. Recent deposition in the low-lying Delta region includes the accumula- tion of organic materials. The depth to first groundwater at the site varies with seasonal q ponditions. Typically the groundwater fluctuates between' and /12' depths, depending upon the recharge conditions. /a�U��C_ No local streams or rivers exist at the site or within the immediate proximity. Several agricultural discharge canals are located within a 5 mile radius of the site. 3.3 Local Wells No domestic water supply wells or irrigation wells are in the immediate proximity of the site. There are however four produc- tion wells upgradient of the site. The distance to these wells is over 1/2 mile and all of these wells draw water from signifi- cant depths (see Figure 3 ) . --- --- - -- - 4 -