Columbia subject headings:
Geology--Arizona--Grand Canyon--History--Congresses.
Paleontology--Arizona--Grand Canyon--History--Congresses.
Harvard subject headings:
Geology--Arizona--Grand Canyon--History.
Paleontology--Arizona--Grand Canyon--History.
Princeton subject headings:
Geology--Arizona--Grand Canyon--History--Congresses.
Paleontology--Arizona--Grand Canyon--History--Congresses.