Timothy O'Sullivan is America's most famous war photographer. You know his work even if you don't know his name: A Harvest of Death, taken at Gettysburg, is an icon of the Civil War. He was also among the first photographers to elevate what was then a trade to the status of fine art. The images of the American West he made after the war, while traveling with the surveys led by Clarence King and George Wheeler, display a prescient awareness of what photography would become; years later, Ansel Adams would declare his work "surrealistic and disturbing."

At the same time, we know very little about O'Sullivan. Nor do we know-really know-much more about the landscapes he captured. Robert Sullivan's Double Exposure sets off in pursuit of these two enigmas. This book documents the author's own road trip across the West in search of the places, many long forgotten or paved over, that O'Sullivan pictured. It also stages a reckoning with how the changes wrought on the land were already under way in the 1860s and '70s, and how these changes were a continuation of the Civil War by other means. Sullivan, known for his probing investigations of place in the pages of the New Yorker and books like Rats and My American Revolution, has produced a work that, like O'Sullivan's magisterial photos of geysers and hot springs, exposes a fissure in the American landscape itself.