These sand tufas are located near Mono Lake in California. They are scattered within an area of about 1/4 square mile. Most of them are only a few feet tall, with the tallest being around three feet. They look other-worldly, and resemble what some say could be alien residences with parking garages. Made of limestone that is formed when calcium-rich spring water mixes with the carbonate-rich Mono Lake water and precipitates around the spring. The towers grew underneath the waters surface.