Dry Tortugas, a group of small coral islands, or keys, in the Gulf of Mexico. They are part of the state of Florida. There are about 10 keys in the Tortugas, which are 65 miles (105 km) west of Key West. Loggerhead Key (about one mile [1,600 m] long) is the largest and has a lighthouse. The Carnegie Marine Laboratory is also on Loggerhead. Fort Jefferson, part of Dry Tortugas National Park (established 1992), is on Garden Key. Fort Jefferson was established in 1846 for defense of the Florida Straits and served as a federal prison during and after the Civil War. The Tortugas were made a federal bird reservation in 1908. Ponce de Leon discovered the islands in 1513. He named them Tortugas (Spanish for “tortoises”) after the numerous turtles in the region.