a commission from the Union Pacific to document the scenery along the various railroad routes for promotional purposes. When his work was discovered by Ferdinand Hayden, who was organizing a geologic survey to explore the Yellowstone River region, he was asked to join the expedition. The following year, he got a last-minute invitation to join the 1870 U.S. government survey (predecessor of U.S. Geological Survey) of the Yellowstone River and Rocky Mountains led by Ferdinand Hayden. He also was a member of the Hayden Geological Survey of 1871 which led to the creation of Yellowstone National Park. Painter Thomas Moran was also part of the expedition, and the two artists worked closely together to document the Yellowstone region. Hayden's surveys (usually accompanied by a small detachment of the U.S. Cavalry) were annual multidisciplinary expeditions meant to chart the largely unexplored west, observe flora (plants), fauna (animals), and geological conditions (geology), and identify likely navigational routes, so as official photographer for the survey, Jackson was in a position to capture the first photographs of legendary landmarks of the West. These photographs played an important role in convincing Congress in 1872 to establish Yellowstone National Park, the first national park of the U.S. His involvement with Hayden's survey established his reputation as one of the most accomplished explorers of the American continent. Among Hayden's party were Jackson, Moran, geologist George Allen, mineralogist Albert Peale, topographical artist Henry Elliot, botanists, and other scientists who collected numerous wildlife specimens and other natural data. Jackson worked in multiple camera and plate sizes, under conditions that were often incredibly difficult. His photography was based on the collodion process invented in 1848 and published in 1851 by Frederick Scott Archer. Jackson traveled with as many as three camera-types—a stereographic camera (for stereoscope cards), a "whole-plate" or 8x10" plate-size camera, and one even larger, as large as 18x22". These cameras required fragile, heavy glass plates (photographic plates), which had to be coated, exposed, and developed onsite, before the wet-collodion emulsion dried. Without light metering equipment or sure emulsion speeds, exposure times required inspired guesswork, between five seconds and twenty minutes depending on light conditions. Preparing, exposing, developing, fixing, washing then drying a single image could take the better part of an hour. Washing the plates in 160 °F hot spring water cut the drying time by more than half, while using water from snow melted and warmed in