A recent gravity survey indicates that sedimentary deposits in the Deadman Lake area of the Twentynine Palms Marine Corps Base, California, are as much as 10,500 feet thick. These deposits fill an ancient valley in the bedrock complex. This valley is alined east-west in the Surprise Spring area and north-south in the Deadman Lake area.
Water levels in the Ames Dry Lake area of the Surprise Spring subbasin have changed little between earliest measurements in 1952-53 and in 1982. Water levels in three Marine Corps Base supply wells in the same subbasin near Surprise Spring declined an average of 78 feet during the past 30 years. Water levels in the same timespan in Deadman subbasin and water quality in the base supply wells, drilled in 1952-53 and 1978, have remained virtually unchanged.
Ground water in storage, suitable for domestic use, in the top 200 feet of saturated sediments in Surprise Spring subbasin was estimated to be 810,000 acre-feet in the early 1950's. About 60,000 acre-feet of this has been removed, mostly for use at the Marine Corps Base, which leaves about 750,000 acre-feet of recoverable water of good quality still stored in the 200-foot interval considered. For planning purposes, it would be safe to use a conservative figure of 300,000 acre-feet for storage in the Deadman subbasin, which contains water having fluoride concentrations greater than the U.S. Environmental Protection Agency's standards for drinking water.
Three sites in the general area of the present well fields seem favorable for recharging the ground-water system in the Surprise Spring subbasin. Further exploration of these sites is suggested.
