It would be arguably the most ambitious public works project in San Diego history. The envisioned pipeline would carry Colorado River water more than 130 miles from the Imperial Valley — through the Anza-Borrego Desert State Park, tunneling under the Cuyamaca Mountains, and passing through the Cleveland National Forest — to eventually connect with a water-treatment plant in San Marcos. An alternative route would run through the desert to the south, boring under Mt. Laguna before emptying into the San Vicente Reservoir in Lakeside. Estimated cost: roughly $5 billion. New water delivered: None.