The basin boundaries for the revised groundwater basin map were primarily defined using geologic contacts
and hydrogeologic divides. Specifically the identification of the groundwater basins was initially based on
the presence and areal extent of unconsolidated alluvial soils identified on 1:250,000 scale geologic maps
provided by the California Department of Conservation, Division of Mines and Geology. The identified groundwater
basin areas were then further evaluated through review of relevant geologic and hydrogeologic reports, well
completion reports, court-determined adjudicated basin boundaries, and contact with local agencies to refine
the basin boundaries.
Metadata Update - December 09, 2010
B118_v3_BasinBoundaries_NAD83_unprojected file was developed from B118v3NAD27UTM10 (dated 15-September-2006) which
had a UTM 10 NAD 27 projection. The new file projection is defined as Latitude/Longitude NAD 83 and was converted
using ESRI's Project tool in a two step process. Set one changed the Datum from NAD27 to NAD 83. The second step was
to re-project the file from Universal Transverse Mercator 10 to Lat/Long Geographic projection for the use of CASGEM.
Metadata Update – June 20, 2012
The shapefile B118_BasinBoundaries_v4_1.shp replaces B118_v3_BasinBoundaries_NAD83_unprojected.shp. Changes in the update include
restoration of the northern portion of the North Yuba subbasin which was inadvertently removed during the 2003 B-118 Update. Also, the
DWR District field (DWR_DIST) in the feature attribute table has been replaced by Regional Office Field (Regional_O). Basin boundary features in
previous versions that were comprised of multiple polygons are now represented by single multi-part polygons.