Soldier Key is an island in Biscayne National Park in Miami-Dade County, Florida. It is located between Biscayne Bay and the Atlantic Ocean, about three miles north of the Ragged Keys, five miles south of Cape Florida on Key Biscayne, seven-and-a-half miles east of the mainland and three miles west of Fowey Rocks. It lies on the Safety Valve, a sand bar that separates Biscayne Bay from the Atlantic Ocean and moderates storm surges into the bay. The island is small, about 200 yards (200 meters) by 100 yards (100 meters) with a maximum elevation of six feet (under two meters). It is at the southern end of the along-shore movement of sand that feeds the barrier islands to the North (such as Key Biscayne) and is the northernmost exposure of the Key Largo limestone (fossilized coral reef) which forms the "true" Florida Keys. The island is covered by grass and shrub vegetation typical of the Florida Keys. Although the island was described as "thickly wooded" in 1894, as of 1955 the only wooded areas were mangroves on the fringes of the island.