Subject Region
United States
59
Pennsylvania
42
Alaska
16
California
11
Mexico
9
Wyoming
9
Texas
7
China
6
Middle East
6
Ohio
5
Alberta
4
Iraq
4
North America
4
Santa Barbara County
4
Warren County
4
Africa
3
Arctic National Wildlife Refuge
3
Canada
3
Norway
3
Oil Creek Valley (Crawford County and Venango County)
3
Prince William Sound Region
3
South America
3
Venango County
3
Washington County
3
Arctic regions
2
Brazil
2
Caribbean Area
2
Chukchi Sea
2
Colombia
2
Iran
2
Kentucky
2
Lima
2
Lima (Ohio)
2
Mexico, Gulf of
2
Northwest Passage
2
Oil Creek Valley (Crawford County and Venango County, Pa.)
2
Oklahoma
2
Timor-Leste
2
Utah
2
Virginia
2
Africa, Central
1
Albany County
1
Allegheny County
1
Andes
1
Appalachian Basin
1
Appalachian Mountains
1
Asia
1
Atlantic Coast
1
Atlantic Coast (Africa)
1
Atlantic Coast (South America)
1
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