This ethnohistory asks how and why a reclusive band of Seri Indians inhabiting San Esteban Island remained unknown to Europeans, Americans, and Mexicans plying the Gulf of California for nearly four centuries. To solve the puzzle, Thomas Bowen explores the history of the Midriff Islands and Gulf of California, the Seri Indians, and Euro-American explorers, settlers, merchants, and scientists of the region. Placing the Gulf of California in a regional and international context, he considers what kinds of people were drawn to the gulf, why they went there, and why so few Euro-Americans visited San Esteban. His own archaeological investigations try to determine whether San Esteban was inhabited permanently by a distinct Seri population or was visited intermittently by Seris from neighboring islands. Bowen richly illustrates his narrative with historical and contemporary photographs and detailed maps of the Gulf of California and San Esteban Island.