Book 4 in the Oz series. Illustrated by John R. Neill. It was published on June 18, 1908 and reunites Dorothy with the humbug Wizard from The Wonderful Wizard of Oz (1900). This is one of only two of the original fourteen Oz books (the other being The Emerald City of Oz (1910), to be illustrated with watercolor paintings. Written shortly after the 1906 San Francisco earthquake, the book starts with an earthquake in California. Dorothy and others are swallowed up by cracks in the earth, and fall into an underground cavern, where they begin their adventures.