The San Joaquin Valley is the southern portion of the Great Central Valley of California. The San Joaquin Valley is a structural trough which is about 200 miles long and 70 miles wide. The Valley is filled with as much as 31,000 feet of marine and continental sediments. Deposits from the Sierra Nevada form alluvial wedges that thicker at the valley margins and thin toward the center of the valley.
The Kings Subbasin groundwater aquifer system consists mostly of unconsolidated continental deposits. These deposits are an older series of Tertiary and Quaternary aged units that are overlain by a younger series of Quaternary deposits. The Quaternary deposits are divided into older alluvium, flood-basin deposits, lacustrine deposits, and younger alluvium.
The older alluvium contain the majority of the groundwater in the subbasin. This subbasin consists of intercalated lenses of clay, silt, silty and sandy clay, clayey and silty sand, sand, gravel, cobbles, and boulders. It is, generally, fine grained near the center of the valley. Closer to Interstate 5, lacustrine and marsh deposits are interbedded with the older alluvium.
The younger alluvium is a sedimentary deposit of fluvial arkosic beds that overlies the older alluvium and is interbedded with the flood-basin deposits. Its lithology is similar to the underlying older alluvium. Beneath river channels, the younger alluvium is highly permeable. Beneath flood plains, it may be of poor permeability. The flood-basin deposits occur along the Fresno Slough and James Bypass. They consist of sand, silt, and clay.
Although the Drought Monitor indicates vast improvement because of heavy winter rains, the groundwater table in the Central Valley continues to decline because it takes many years of wet weather to replenish our aquifers.
- California just ended it's sixth year of drought with amazing winter rains and flooding.
- California saw 2016 as the warmest year on record.
- On January 17, 2014 California State Governor, Jerry Brown, declared a drought state of emergency.
- On May 9, 2016, California State Governor, Jerry Brown issued an order to continue water savings as drought persists.
The lacustrine and marsh deposits contain silts and clays and restrict the vertical movement of water. A major unit is the Corcoran Clay (E-clay) member of the Tulare formation. This is the most extensive of the clay deposits and exists in the western one-quarter to one-third of the Kings Subbasin. The Corcoran Clay ranges from about 200 to 550 feet below the ground surface. The A-clay and C-clay are less extensive and lie above the Corcoran Clay. These clay layers cause confined groundwater conditions beneath them.
Groundwater recharge occurs from river and stream seepage, deep percolation of irrigation water, canal seepage, and intentional recharge. The Cities of Fresno and Clovis, Fresno Irrigation District, and Fresno Metropolitan Flood Control District have a cooperative effort to utilize individually owned facilities to recharge water in the greater urban area. Fresno Irrigation District, Consolidated Irrigation District, and others have recharge efforts on going. The Fresno-Clovis metropolitan area uses a regional sewage treatment facility to deposit water into percolation ponds southwest of Fresno.
Central Valley Facts
- California’s Central Valley covers about 20,000 square miles, and is one of the most productive agricultural regions in the world.
- More than 250 different crops are grown in the Central Valley, with an estimated value of $17 billion per year.
- Approximately one-sixth of the Nation’s irrigated land is in the Central Valley.
- About one-fifth of the Nation’s groundwater pumpage is from the Central Valley aquifer system.