National code
S100CNRLVLUSGS National Water Information System referenceAquifer map & monitoring
Central Valley aquifer system
This is a regional body of water-bearing rock or sediment—not an underground lake. The mapped shape shows the shallowest principal aquifer where it reaches the surface or lies beneath shallow deposits. It does not show the full underground extent.
Open in the atlas →Groundwater levels at monitoring wells
47 wells are shown here. Individual well measurements describe a site, not one aquifer-wide water level.
Monitoring coverage is not a measure of groundwater availability or quality. Check USGS for current monitoring records.
Wells within the mapped area
47 wellsWells inside the mapped boundary; they may not represent the whole aquiferRock or sediment
Unconsolidated sand and gravel aquifersCaliforniaWhat the wells can say
What well measurements tell us
A water level at one well can be compared with that well’s own usable history. It does not establish aquifer-wide condition, storage, depletion, or available supply.
Coverage, not condition
0 wells with usable history
Knowing a well has a measurement series is not enough to show a trend. We check the individual measurements and time span before calculating seasonal comparisons.
Sources and map limits
Geography: U.S. Geological Survey principal aquifers (2003). Codes: USGS National Aquifer Code Reference List. A well inside this mapped boundary does not necessarily draw from this aquifer. Well-construction records are needed to confirm which aquifer it reaches.