Rock Springs is the source of Rock Springs Run, a swift-running stream with an average flow of 26,000 gallons per minute and a constant temperature of 68 degrees, and the spring flows from limestone containing fossils dating back 17 million years. In 1855, the State of Florida awarded land near Rock Springs to William S. Delk, a veteran of the Second Seminole War, to encourage settlement in the state's interior. Delk later became the owner of the area's largest plantation and used Rock Springs Run to power his grist mill, sawmill, and cotton gin. After Delk's heirs sold the land to lumber companies, New Jersey doctor Howard A. Kelly visited Rock Springs in 1910. Kelly, a founder of Johns Hopkins Hospital, an internationally recognized gynecologist, and an avid naturalist, was taken with the sweet spring water from the mysterious cave. He purchased 200 acres around Rock Springs in 1921 for use as a wildlife preserve and bird sanctuary, and he and his wife gave the land to Orange County in 1927 on the understanding that it would remain a public park open to every citizen.