his hands slowed down the processing substantially. His photographic division of 5 to 7 men carried photographic equipment on the backs of mules and rifles on their shoulders. Jackson's life experience (for example his military service, and his peaceful dealings with Indians) was welcomed. The weight of the glass plates and the portable darkroom limited the number of possible exposures on any one trip, and these images were taken in primitive, roadless, and physically challenging conditions. Once when the mule lost its footing, Jackson lost a month's work, having to return to untracked Rocky Mountain landscapes to remake the pictures, one of which was his celebrated view of the Mount of the Holy Cross. Despite the delays and setbacks Jackson returned with conclusive photographic evidence of the various western landmarks that had previously seemed only a fantastic myth: the Tetons, Old Faithful and the rest of the Yellowstone region, Colorado's Rockies and the Mount of the Holy Cross, and the uncooperative Ute Indians. Jackson's photographs of Yellowstone helped convince the U.S. Congress to make it the first national park in March 1872. Work in Colorado Jackson exhibited photographs and clay models of Ancestral Puebloan dwellings at Mesa Verde in Colorado in the 1876 Centennial Exposition in Philadelphia. He continued traveling on the Hayden Surveys until the last one in 1878. He later established a studio in Denver, Colorado and produced a huge inventory of national and international views. He incorporated himself as W.H. Jackson Photograph and Publishing Company in 1883. Commissioned to photograph for western state exhibitions at the World's Columbian Exposition of 1893 in Chicago, he eventually produced a final portfolio of views of the just-shuttered "White City" for Director of Works and architect Daniel Burnham. Railroad line commissions From 1890 to 1892 Jackson produced photographs for several railroad lines (including the Baltimore and Ohio (B&O) and the New York Central) using 18 x 22-inch glass plate negatives. The B&O used his photographs in their exhibit at the World's Columbian Exposition. World's Transportation Commission From 1894 to 1896 Jackson was a member and photographer for the World's Transportation Commission, organized by Joseph Gladding Pangborn, a publisher for the Railroad. The purpose of the trip was to document traditional and novel forms of transportation internationally, though many photographs did incorporate the local environment and people. Commission members left New York on September 25, 1894, and traveled across the world. They