The river flows through the Parker Valley, much of which belongs to the Colorado River Indian Reservation, and then the Palo Verde Valley, where it is crossed by Interstate 10 near Blythe, California. The small Headgate Rock Dam removes water for irrigation in the Parker Valley and the Palo Verde Dam provides water to the Palo Verde Valley. The river then flows through a canyon in the Trigo Mountains, where the Cibola and Imperial National Wildlife Refuge encompass the wetland areas formed above Imperial Dam, which filled with silt shortly upon its completion in the 1930s. Most of the Colorado's remaining flow is removed for irrigation here. The Gila Gravity Main Canal provides water for the Gila Valley in Arizona. The All-American Canal, which runs west to the Imperial Valley of California, is the largest irrigation canal in the world, capable of carrying - the entire natural flow of the Colorado prior to damming. The canal supplies more than half a million acres (2000 km2) which due to its mild climate grows most of the winter produce in the United States.