A water budget analysis of a portion of the Campo Indian Reservation in southeastern San Diego County was completed for the 1992-1993 year. The objective of this analysis was to determine the specific yield of the study area. Data was collected from local agencies as well as from various reports produced by Golder Associates and Dames and Moore. The computer program Surfer was used to generate contour maps and to determine water volume changes. The program Recharg3 was used to determine monthly recharge values. Excel spreadsheets were created to calculate the water budget and values of specific yield. The water budget was calculated on a monthly basis, a 3-month running average, and on a yearly basis. Calculated specific yield ranged from a low of0.029 to a high of 0.270. Negative specific yield values resulted from the monthly and the 3-month running average. Negative specific yield results indicate that the water budget equation is incorrectly calculating change in volume, likely due to a lag time between recharge and water level response. It was, however, possible to determine nonnegative specific yields on a yearly basis for the 1992-1993 year. Specific yields for a year were calculated using maximum runoffs of 15, 20, and 25% in recharge calculations. Specific yields for the year water budget ranged from 0.075 to 0.092 (25% and 15% maximum runoff, respectively).