This work is a daily record of Ferdinand Hayden's historic 1871 scientific expedition through Utah, Idaho, and Montana Territories to the Yellowstone Basin. The expedition's findings quickly led Congress to establish Yellowstone as the world's first national park. In addition to its scientific discoveries, the expedition is famous for producing the earliest on-site images of Yellowstone, by its photographer, William Henry Jackson, and its guest artist, Thomas Moran. Marlene Deahl Merrill has woven together a compelling daily narrative from the field writings of three expedition members: unpublished journals kept by mineralogist Albert Peale and geologist George Allen, periodic reports by Peale to his hometown newspaper, and letters from Hayden to his friend and mentor Spencer Baird at the Smithsonian Institution. Enriching this narrative are Jackson's photographs of camp scenes and landscapes; rare panoramic drawings by the party's topographical artist, Henry Elliott; maps; an introduction; and extensive annotations.