Albumen stereoview [9 1/4 cm x 15 cm] on a yellow mount [10 cm x 18 cm] Geographical and Geographical Explorations and Surveys West of the 100th Meridian backstamp. Printed label on the reverse. Expedition of 1871. From the Smithsonian American Art website- "In 1871 O'Sullivan joined the geological surveys west of the one hundredth meridian, under the command of Lieutenant George M. Wheeler of the U.S. Corps of Engineers. An army man rather than a civilian scientist like King, Wheeler insisted on a survey that would be of practical value. His reports included information likely to be useful in the establishment of roads and rail routes and the development of economic resources. Wheeler's captions for O'Sullivan's pictures provide geological information but also emphasize that the West was a hospitable place for settlers."