See also “Bibliographies.”

National Park Service History Electronic Library & ArchiveLinks to an external site. — Awesome source for most (all?) of the parks. Choose a park, and then down to “documents” any one of these.

Yellowstone Superintendent Annual ReportsLinks to an external site., 1872-1893 — begins with Nathaniel P. Langford, 1872-72

“History of National ParksLinks to an external site.” — NPS encyclopedia of lots of park documents.