How Groundwater Basins are Formed
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 The amazing geology of Yosemite National Park reveals that, 500 million years ago, activity beneath the surface of the earth started to create California’s unique and extreme landscape variations.  Seventy million years ago, during a period of geologic history called the Cenozoic era, nature’s forces pushed and pulled rapidly at rock formations deep underground creating uplifts (mountains), depressions (valleys) and numerous fault regions.  Volcanic and sedimentary rock formations were folded, metamorphosed (pressurized) and complexly faulted, forming tall mountains, vast valleys and underground basins.

In the Livermore Valley, water in river channels of the distant past deposited large amounts of highly porous sand and gravel.  These deposits, found below the ground surface, constitute major aquifers and provide large amounts of groundwater to wells.  The Livermore Valley has two major sources of groundwater.  One source is the alluvial deposits that make up the Valley floor.  The second source is called the Livermore Formation.  This formation is adjacent to and underlies the Valley floor.  The central and western portions of the Livermore Valley contain the greatest amount of valley fill materials and produce the largest quantities of water.