George B. Dixon
"The official (and later renowned) photographer, William Henry Jackson, worked closely with his assistant, Robert Dixon, developing his photographs on-site and consulting with the visiting landscape artist, Thomas Moran. this threesome operated quite independently, taking their own side trips and receiving little if any directions or suggestions from Hayden." 
"Started back to camp at 3 1/2 oclock, clouds began to gather & and rain set in in the Mts. all around us but did not fall heavily on us. Jackson's pack mule & traps got pretty well shaken up in the return having to force a passage between trees not wide enough apart to allow free passage of the pack. When about half way back Dixon's horse got his foot fast between two fallen trees & in his frantic efforts to extricate himself he struck Dixon, who had dismounted to help him, square on the head with his forefoot, peeling his scalp & hurting him considerably." --Thomas Moran, July 19, 1871 
- Merrill, Marlene. With Hayden in the Field : a Case Study Based on Unpublished Letters and Diaries from the 1871 Yellowstone Survey. 1993. Yellowstone Research Center Archives.
- "U.S. Geological Survey Photographic Library," U.S. Geological Survey Photographic Library, 1871, accessed November 21, 2012, photo by W. H. Jackson, http://libraryphoto.cr.usgs.gov/htmllib/btch198/btch198j/btch198z/btch198/jwh00598.jpg
- Moran, Thomas, 1837-1926. Moran's Diary 1871. Yellowstone Research Center Archives.