The Temblor Range and surrounding region contains extensive outcrops of the Monterey Formation (Miocene age, about 20 to 9 million years). Rocks from the Monterey formation consist mostly of silicate shales and porcellanite (silica derived from fossil plankton in an intermediate to deep-water marine setting). Fossils and sediments from the Monterey Formation show that the Carrizo Plain region was a marine basin with shallow to intermediate depths (marine waters covered the southern San Joaquin Valley region). Marine sediments younger than about 9 million years are not preserved in the Carrizo Plain National Monument area, but they occur throughout the Kettleman Hills region (about north of the park). The Pliocene-age Etchegoin Formation contains marine fossils to about 4 million years old. Fossils of the Etchegoin Formation are supporting evidence that the Coast Ranges and the Temblor Range are young, having been uplifted mostly during the Pleistocene Epoch (or Quaternary Period) in the past several million years. Much of that ongoing uplift is due to tectonics associated with the San Andreas Fault and other fault systems in the region.