The San Joaquin Valley is bordered on the west by the Coast Range and on the east by the Sierra Nevada mountains. The Coast Range include Cretaceous and Tertiary marine sedimentary rocks. Weathering and oxidation of the Moreno Formation, a black marine shale, produces Pyrite, FeS2, and Iron Selenide, FeSe2. As the weathered products concentrate in evaporative minerals and salts, selenates (for instance, Na2SeO4 · 10 H2O or Na2Mg(SeO4)2 · 4 H2O) and Sulfates (Na2SO4 · 10 H2O or Na2Mg(SO4)4 · 4 H2O) can form. This results in selenium salts and selenium rich soils that are sloughed off the mountains via debris flows or landslides into the San Joaquin valley. Additionally, the San Joaquin Valley has a shallow aquifer bounded by impermeable clays.