RD 787 is located in the northeastern portion of Yolo County, west of the town of Knights Landing and adjacent to the Sacramento River.  The District covers approximately 8,950 acres, most of which is irrigated agricultural land.

RD 787 overlies the Sacramento Valley Groundwater Basin, Colusa Subbasin.  The Colusa Subbasin is part of the larger Sacramento Valley Basin, which includes areas underlying the Sacramento Valley, the Sacramento River, and its tributaries as they flow south and west toward the Sacramento-San Joaquin Delta.  The Colusa Subbasin is bounded on the east by the Sacramento River, on the north by Stony Creek, on the west by the Coast Ranges, and on the south by Cache Creek. The Colusa Subbasin is about 1,400 square miles in area, and underlies portions of Tehama, Glenn, Colusa and Yolo Counties.

The north and east boundaries of RD 787 are formed by the Sacramento River.  On the south and west sides of the District, the adjacent water districts and suppliers are Reclamation District No. 108, Colusa Drain Mutual Water Company, Yolo-Zamora Water District, and Knights Landing Community Service District (Figure 2).  To the east across the Sacramento River, the nearest mutual water companies are the Pelger, Sutter, Pleasant Grove-Verona and Natomas Central Mutual Water Companies.  Collectively, these purveyors supply groundwater and surface water for municipal and irrigation supply within their boundaries.