A dead Confederate sharpshooter at the foot of Little Round Top at the Battle of Gettysburg in 1863. (Timothy H. O'Sullivan/LOC)
After joining a surveying team in Panama to assess the difficulty of digging a canal in the isthmus, O'Sullivan returned to photograph the American West, jointing Lt. George Wheeler's survey team. After facing near-starvation when his survey boat capsized on the Colorado River, O'Sullivan accepted a post with the U.S. Geological Survey in Washington, D.C.
The Pyramid and Domes, a line of dome-shaped tufa rocks in Pyramid Lake, Nevada, seen in 1867. (Timothy O'Sullivan/Library of Congress)
Nearly 150 years ago, O'Sullivan came across a Spanish inscription from 1726. This close-up view of the inscription carved in the sandstone at Inscription Rock (El Morro National Monument), New Mexico reads, in English: "By this place passed Ensign Don Joseph de Payba Basconzelos, in the year in which he held the Council of the Kingdom at his expense, on the 18th of February, in the year 1726". (Timothy O'Sullivan/Library of Congress)