Wells in Potrero Canyon are the main source of water for the Morongo Band of Mission Indians, located near Banning, California. A series of pumping tests were completed on four water-supply wells in the Canyon during February 27 to March 2, 2001. The purpose of the tests was to determine the productivity of each well and the interference (drawdown or water-level decline) each pumped well produced in surrounding wells. During each pumping test, a well was pumped at a fairly constant rate for several hours and drawdown was measured in the pumping well; nearby production wells (mostly idle) were used as observation wells. Productivity of the pumping well, specific capacity in gallons per minute per foot of drawdown (gal/min/ft), was determined from time-drawdown data in the pumping well. The range of specific capacities from these tests were 29.9 gal/min/ft, measured in well 24P3 (2S/1E-24P3) to 12.8 gal/min/ft in well 25H1. A specific capacity of 34.4 gal/min/ft was reported (Constant Flow Test notes by McCalla Bros.) for well 24N1. The amount of the drawdown in the observation wells during each pumping test was used to determine the interference between wells.