Man who found the Titanic is now mapping "The Unknown America" undersea

Robert Ballard has embarked on a new wave of American exploration, inspired by the epic journey of Lewis and Clark more than 200 years ago. This time, it's not over land, but in a part of the country that lies in the deep sea.

You may know Ballard as the man who found the Titanic. We first spent time with him a few years ago when he took us on a search for ancient shipwrecks in the Aegean Sea, but at the age of 72, he's changed course and come home. Why? Because the U.S. has jurisdiction over more ocean than any other country on Earth and beneath the waves lies trillions of dollars in untapped natural resources and, as we saw on our journey, a wealth of American history.

Robert Ballard calls it "the unknown America." We joined him about 100 miles off the coast of Mississippi in the Gulf of Mexico.