 The second was Marine Corps Air Station Tustin, an airship base, which was built over the deepest part of the Cienega de las Ranas.After World War II, the San Diego Creek watershed experienced rapid urbanization.As the Irvine Company sought to develop the of the former Irvine Ranch, an ambitious effort was made to drain the former Cienega via a series of pumping plants and ditches, and later the construction of the flood control channels that today make up the San Diego Creek system.