Columbia subject headings:
Botany--North America.
North America--Description and travel.
Northwestern States--Description and travel.
Oak.
Pine.
Harvard subject headings:
Botany--North America
North America--Description and travel
Northwest, Pacific--Description and travel.
Oak
Pine
Princeton subject headings:
Botany--North America.
North America--Description and travel.
Northwestern States--Description and travel.
Oak.
Pine.