The Raymond Basin covers approximately 40 square miles. It is bounded on the north by the San Gabriel Mountains, on the south and east by the San Gabriel Valley and on the west by the San Rafael Hills. Because of its natural formations and barriers, the Raymond Basin is replenished by surface water flows from the San Gabriel Mountains, including the Arroyo Seco, Eaton Wash and Santa Anita Wash.

The Basin supplies over half of the overlying area’s total annual water needs and is one of the most valuable local resources. As much as 1,500,000 acre feet of water can be collected in this underground water table. Water is pumped by 16 different water purveyors to serve customers’ daily needs throughout the area.