 These estuaries are formed by subsidence or land cut off from the ocean by land movement associated with faulting, volcanoes, and landslides.Inundation from eustatic sea-level rise during the Holocene Epoch has also contributed to the formation of these estuaries.There are only a small number of tectonically produced estuaries; one example is the San Francisco Bay, which was formed by the crustal movements of the San Andreas fault system causing the inundation of the lower reaches of the Sacramento and San Joaquin rivers.