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(CSWRCB, 1989). The Chico area is situated on recent <br /> sway / ao'� alluvial fan materials derived from volcanic sediments and <br /> mudf]ows originating in the hills to the east of Chico(DW R, <br /> J y� 1984). The alluvial deposits average about 40 to 50 feet in <br /> BOLINAS MESA � .�` thickness and consist of unconsolidated cobbles,gravel and <br /> sruov AREA 8Nd, sand,and minor amounts of clay.These deposits support a <br /> ► 9N' shallow unconfined direct]aquifer that is recharged P '>' q g Y by <br /> infiltration from precipitation,local runoff,and discharge <br /> c �;`, / •,� from subsurface sewage disposal. Older alluvium imme- <br /> diately underlies the recent alluvium and extends to depths <br /> of nearly 450 feet. It is characterized mostly by thick clay <br /> B�INAs layers and cemented sand and gravel.In this zone,ground <br /> ` <br /> _=== - <br />