Carleton E. Watkins was an American photographer of the 19th century. Born in New York, he moved to California and quickly became interested in photography. He focused mainly on landscape photography, and Yosemite Valley was a favorite subject of his. His photographs of the valley significantly influenced the United States Congress' decision to preserve it as a National Park. In July 1861, Watkins made the decision that changed his career: he traveled to Yosemite. He brought his mammoth-plate camera (which used 18×22 inch glass plates) and his stereoscopic camera. The stereoscopic camera was used to give the subject depth, and the mammoth-plate camera was used to capture more detail. The photographer returned with thirty mammoth plates and one hundred stereoview negatives. These were some of the first photographs of Yosemite seen in the East. In 1864, Watkins was hired to make photographs of Yosemite for the California State Geological Survey.