Tassajara Formation
Encyclopedia
The Tassajara Formation is a geologic unit within the Livermore Valley
of Northern California
, USA. The formation surfaces only in the northern upland parts of the Livermore Valley and underlie the central part of the valley floor at a depth ranging from 250 feet (76.2 m) to 700 feet (213.4 m). The Tassajara Formation consists of sediments ranging from brown to gray mudstone
, andesitic sandstone
, conglomerate
, and minor bentonitic and pumiceous tuff. In the northern San Ramon area, the Tassajara Formation underlies Quaternary
valley fill material.
The Bishop Subbasin
is an aquifer
that resides between two subsurface ridge formations of the Tassajara Formation in the northern extremity of the Amador Valley.
Livermore Valley
The Livermore Valley AVA is an American Viticultural Area in Alameda County, California, surrounding the city of Livermore in the Tri-Valley region. Both the AVA and the city are named after Robert Livermore, a landowner whose holdings encompassed the valley. The groundwater basin underlying the...
of Northern California
Northern California
Northern California is the northern portion of the U.S. state of California. The San Francisco Bay Area , and Sacramento as well as its metropolitan area are the main population centers...
, USA. The formation surfaces only in the northern upland parts of the Livermore Valley and underlie the central part of the valley floor at a depth ranging from 250 feet (76.2 m) to 700 feet (213.4 m). The Tassajara Formation consists of sediments ranging from brown to gray mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
, andesitic sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
, conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
, and minor bentonitic and pumiceous tuff. In the northern San Ramon area, the Tassajara Formation underlies Quaternary
Quaternary
The Quaternary Period is the most recent of the three periods of the Cenozoic Era in the geologic time scale of the ICS. It follows the Neogene Period, spanning 2.588 ± 0.005 million years ago to the present...
valley fill material.
The Bishop Subbasin
Bishop Subbasin
The Bishop Subbasin is an aquifer that resides between two subsurface structures of the Tassajara Formation in the northern extremity of the Amador Valley. This aquifer is a sub-unit of the Livermore-Amador Groundwater Basin. The Bishop Subbasin is associated with the locale of San Ramon,...
is an aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
that resides between two subsurface ridge formations of the Tassajara Formation in the northern extremity of the Amador Valley.
See also
- Arroyo de la LagunaArroyo de la LagunaArroyo de la Laguna is a southward-flowing stream in Alameda County, California, USA which originates at the confluences of South San Ramon Creek and Arroyo Mocho. The Arroyo de la Laguna is fed by tributaries in the Amador Valley and certain eastern slope drainages of the Diablo Range; these...
- Arroyo del ValleArroyo del ValleArroyo del Valle or Arroyo Valle is a westward-flowing stream in Alameda County and Santa Clara County, California, USA, that is tributary to Arroyo de la Laguna which in turn flows into Alameda Creek. The stream drains much of the southern portion of the city of Livermore, and it also flows...
- Arroyo MochoArroyo MochoArroyo Mocho is a stream in eastern Alameda County, California that traverses the cities of Livermore and Pleasanton.The underlying aquifer is the Mocho Subbasin, whose eastern boundary is the Tesla Fault...
- Mocho SubbasinMocho SubbasinThe Mocho Subbasin is the largest of the groundwater subbasins in the Livermore Valley watershed. This subbasin is bounded to the west by the Livermore Fault Zone and to the east by the Tesla Fault...
- South San Ramon CreekSouth San Ramon CreekSouth San Ramon Creek is a southward-flowing stream in Alameda County and southern Contra Costa County, California, USA. The creek is a tributary to Arroyo de la Laguna and is being actively protected as of 2007 by the city of San Ramon and other entities to preserve riparian zone habitat...