La Sal del Rey (the salt of the King) is a hypersaline lake sitting over a solid dome of salt estimated at 4 million tons. Exactly how the massive salt deposit originally formed remains unknown, but it is probably a remnant of an ancient seabed. With salt crystals that are 99 percent pure sodium chloride, the lake can be 10 times saltier than seawater. Salt blocks removed from any spot in the lake are quickly replenished, often in two or three days.
From ancient times, native Americans have mined salt here. During the 1700's, Spanish explorers claimed the salt deposit for the King of Spain. Tracks left by heavily-laden wagons headed for Mexico City can still be seen dug into the banks of the lake. During the Civil War, camels were used to carry the salt to Confederate troops. The lake has been used as a therapeutic wading pool to cure arthritis and to decorate items such as branches, which are thrown into the lake and can be recovered a day or two later encrusted in sparkling crystals.
Today, the lake is a National Wildlife Refuge, managed by the U. S. Fish & Wildlife Service.