What kinds of rocks and soils are found in the aquifer?
The San Joaquin Valley is a large area, and the soils and rocks vary. On the eastern side, the soils come from the Sierra Nevada. They mostly consist of highly permeable, medium to coarse-grained sands. Soils on the western side of the valley come from the coast ranges and have a higher clay content and finer texture than on the eastern side. In the center part of the San Joaquin Valley near the rivers, Holocene stream deposits of coarse sand, gravel, and silt are present. Away from the rivers, flood basin deposits, which are moderately to densely compacted clays, are found. There are also areas near Fresno and around the Merced River. These sands are fined-grained and well-sorted. The San Joaquin Valley also contains marine sediments, a result of being covered by the ocean at times during the past. The Central Valley is surrounded and underlain with consolidated volcanic and metamorphic rocks. These rocks are almost impermeable. The aquifer is heterogeneous. The hydraulic conductivity
