Fig. 1.

Overview of the study area. (A) Location of the study area in the western San Joaquin Valley that includes 13 water districts (W.D.). (B) Soil texture map. (C) Soil gypsum contents. The main soil types are clay (52% of the study area), clay loam (35%), loam (4%), and sandy loam (9%). The finer-textured soils are found in the valley trough near the San Joaquin River. These soils have clay contents from 40% to 60%. The clay fraction is dominated by the montmorillonite mineral. Going from east to west, the soils gradually become more coarsely textured. A distinct feature is the sandy loam soils developed in stream deposits of Panoche Creek. Organic matter contents are low. Gypsum is predominantly present in the downslope soils. Soil data are from ref. 14.