Native peoples lived on the shores of Upper Newport Bay for more than 90 centuries, with the most recent group, the Tongva, arriving about 3,500 years ago and living in seasonal village sites before the Spanish missions were established, fishing, hunting, and gathering food from the bay and surrounding mesas. In the 1800s, Mexican land grants created ranchos in Alta California, including Jose Sepulveda's Rancho San Joaquin around Upper Newport Bay, but drought forced Sepulveda to sell it in 1864 to James Irvine, Thomas and Benjamin Flint, and Llewellyn Bixby. Lured to California by gold, Irvine instead made a fortune in real estate, and near the end of the Civil War he and his partners bought two failing ranchos, one including the Upper Newport Bay estuary totaling 96,000 acres. In the 1930s, the Irvine Company, already involved in many enterprises, built and operated a salt works on the flatland below the bluff, opening it in 1935 and using evaporation ponds to extract up to 5,000 pounds of salt per year; a portion of the earthen dike that trapped seawater in holding ponds can still be seen. Beginning in the 1940s, shells dredged from the estuary were ground and added to commercial chicken feed. Too little water had helped undermine local cattle ranchos in the 19th century, but too much water, in the form of a massive flood in 1969, damaged the dike and ended industrial exploitation of the estuary. From the 1950s onward, development in Newport Beach, Costa Mesa, and Irvine posed new challenges to protecting the bay, and in 1967 Frank and Fran Robinson joined other local citizens to form the Friends of Newport Bay to promote the bay's natural values and protect it from development into a commercial marina. Protection expanded when the Upper Newport Bay Ecological Reserve was dedicated in 1975 to protect 752 acres of the Back Bay, followed in 1989 by dedication of an additional 140 acres of uplands as the Upper Newport Bay Nature Preserve. Today the Back Bay supports more than 1,000 species of plants and wildlife, along with the Muth Interpretive Center, the Back Bay Science Center, and trails for hiking, biking, equestrian use, and water travel.