Era
Cretaceous
15
Quaternary
12
Precambrian
10
Eocene
6
Tertiary
5
Pennsylvanian
4
Jurassic
3
Ordovician
3
Paleozoic
3
Permian
3
1979
2
Cambrian
2
Cenozoic
2
Civil War, 1861-1865
2
Paleocene
2
1815-1871
1
1871-1918
1
1918-1945
1
1933-1945
1
1963
1
1970
1
1971
1
1979-
1
20th century
1
800-1444
1
Devonian
1
Mesozoic
1
Miocene
1
Oligocene
1
Pleistocene
1
Pliocene
1
Pre-Quaternary
1
Silurian
1
To 146 B.C.
1
Triassic
1
War of 1812
1