By increasing the stress tending to compact the un• consolidated deposits by as much as 50 percent, man has created the world's largest area of intense land subsid• ence in the west-central San Joaquin 'Valley. With• drawal of ground water for agriculture has caused more than 2,000 square miles to subside more than 1 foot. As • 1966. the area that had subsided more than 10 feet - -o miles long and included 500 square miles; maximum subsidence was 26 feet.
Water-level changes in the aquifer systems have in• creased the applied stresses and have caused acceler• ated compaction of the deposits. Detailed knowledge of the interrelations of water-level change, change in aquifer-system thickness, and the concurrent changes in the altitude of the land surface is necessary for a better understanding of the mechanics of aquifer sys• tems and the compaction of sediments, as well as for the de , elopment or criteria in predicting future land subsidence.
This paper is the third of three reports discussing land subsidence due to ground-water withdrawal in the Los Banos-Kettleman City area, California. Part 1 (Bull and Miller, 1974) is a factual presentation of the hy• drologic factors conducive to land subsidence in the study area. Part 2 (Bull, 1974) contains basic data and interpretation about the land subsidence and compac• tion that have been measured in the area and discusses geologic factors influencing the amounts, rates, and distribution of compaction.

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