Columbia subject headings:
Geology--Colorado, Northwestern--Congresses.
Geology--Colorado, Northwestern--Guidebooks.
Harvard subject headings:
Geology, Stratigraphic--Congresses
Geology--Colorado--Congresses.
Petroleum--Geology--Colorado--Congresses.
Princeton subject headings:
Geology--Colorado, Northwestern--Congresses.
Geology--Colorado, Northwestern--Guidebooks.