flooding adjacent lands during occasional years with heavy winter rains. Three dump sites about upstream from the mouth of the river came under the control of the Ventura Regional Sanitation District by 1988. They continued to use the sites until they were closed in 1996. Municipal wastewater treatment facilities, industrial dischargers, and power generating stations are point source dischargers along the coast of the Oxnard plain. Water quality at the numerous beaches has been very good with a few exceptions. Two power generating stations were built in the 1960s to take advantage of the ocean for cooling. The Oxnard City council tried to prevent a third plant from being built in 2012. After years of legal tussles, the McGrath Peaker Plant was built by Edison next to the existing power plant at Mandalay. Geography This plain is bounded by the Santa Monica Mountains, the Santa Susana Mountains, the Topatopa Mountains to the north, the Santa Clara River Valley to the northeast and the Santa Barbara Channel to the south and west. The topography of the plain is relatively level. It has been formed chiefly by the deposition of sediments from Santa Clara River Valley and the watershed of Calleguas Creek before they flow into the Pacific Ocean. The alluvial deposits from these rivers are generally a few hundred feet () thick and lie over Pleistocene and Pliocene sedimentary rocks. The Santa Clara River is one of the largest river systems along the coast of Southern California and only one of two remaining river systems in the region that remain in their natural states and not channelized by concrete. Prior to the agricultural expansion, installation of drainage systems, and other disturbances, this broad, flat, coastal area contained a series of marshes, salt flats, sloughs, and lagoons. Historically, Calleguas Creek flood flows spread across the floodplain and the deposited sediment created the rich agricultural lands of the Oxnard Plain. With year-round agriculture in the floodplain, concrete channels and dirt levees have been built to contain the flow. This has delivered increased sediment to Mugu Lagoon and flooding during extreme rain events. With the Port of Hueneme, Channel Islands Harbor, and Ventura Harbor along with a number of breakwaters, jetties and groins, this is one of the most engineered coastlines in the state with complicated coastal geography. Groundwater Saltwater intrusion from the ocean has occurred in the southern Oxnard Plain due to the