WORK PLANS - Laserfiche WebLink

Home Browse Search

sin BACKGROUND Flood Basin Deposits. 'Mis unit is exposed in the Della area of the San Joaquin Valley. These deposits are basin-wide, law granted forms of the Laguna, Riverbank, Modesto, and Recent Fonnmions and, therefore, wage in age from Pliocene to Recent They are generally much game grainedwith a higher percentage of fine sand and clays than their depositional equivalents to the east and man Occasional gravel beds occur along the present waterways and arc probably represenmtive of the type of underlying Infantry distributes. 'I Iris unit singes in thickness Bom 0 to 1,400 Fort. Groundwater in this unit occurs under unconfined to confined conditions. The unit, in general, has low permeability and may create semi-confined to confined conditions when interfingered with the Alluvium and Morkmos Riverbank Fonmations. Occasional pockets off Il water arc found in the Delta deposits, but generally speaking the formation contains poor quality water. Laguna Formation. The Laguna Formation is Plio-Pleistocene in or and consists of discontinuous lenses of stream laid sand and silt with lesser amounts of clay and gravel. There are no rcgiorelty significant fine-grained intervals that could cause water pressure conditions, although the hemmgenwns nature of the sediments causes local confinement Fmm the Mokelumne River area, the formation thickens from approximately 400 f to approximately 1,000 feet in the Stockton tsar. Groundwater occurs under unconfined to locally serniconfined conditions within this unit. Occasional minor perched water zones are encountered in this formation, particularly in the Mokelumne River mar Mehrten Formation. 'Ibis formation is late Miocene to Pliocene in age and is compouN of moderately to wet] indurated andesiac sand to Mandstone ImerbeddW with conglomerate, tuRaceous dirstone, and claysmne. The Mehrmn Formation is appmxintately 400 feet thick in moral surface outcrops m over fi0O feet thick in the subsurface near Stockton. It is mpomd to he 1 300 feet thick at McDoruld Island. The top of the Weser Formation occurs at depths of approximately 800 to 1,000 lest in the Stockton area. Regional studies indicate that Mehden Formation sands commonly yield on the order of 1,000 gallons per minute fiom wells. Ile formation appears to be cemiconfined at least locally in the Stockton area, due to tine inferred extensive fine-grained beds in its upper pad.