The study area is located in the Grassland Subarea (SJVDP, 1990): the GBP study area is bounded on the east by the San Joaquin River from the Mendota Pool to Crows Landing; the Westlands Water District to the south; Interstate 5 to the west; and approximately the Stanislaus/Merced county line to the north. This area includes the Panoche Drainage District, the Broadview Water District, the Firebaugh Canal Water District, a portion of the Central California Irrigation District, the Pacheco Water District, the Charleston Drainage District, and the Grasslands Water District, as well as several state and federal wetland refuges.