Cave-in-Rock State Park preserves a famous riverside cave in limestone bluffs above the Ohio River and the layered history attached to it. Shaped chiefly by wind, water, floodwaters, and the effects of the 1811–12 New Madrid earthquakes, the cave was known to Native Americans long before the French explorer M. de Lery mapped and named it in 1729. During the flatboat era, it became both a key landmark and a feared outlaw refuge, notably for Samuel Mason’s band. With steamboat travel, it turned into a popular sightseeing stop. Since Illinois began acquiring the site in 1929, it has remained important for its geology, frontier associations, and river heritage.