Hannibal , Missouri , on the Mississippi River was the home of Samuel Clemens from age 4 to 17. In 1832 a large cave was discovered and named Simms Cave a place of fascination for the local children. Writing as Mark Twain, Clemens describes Tom and Becky's adventure lost in McDougal's Cave - clearly a reference to his own memories of Simms Cave . Today, the Mark Twain Cave is a popular tourist site and is marked by a large bur oak at the entrance, known as the Mark Twain Cave Bur Oak.