Era
Cretaceous
52
Quaternary
40
Jurassic
19
Paleozoic
18
Precambrian
17
Eocene
14
Tertiary
14
Cenozoic
13
Pennsylvanian
13
Paleocene
11
Permian
10
Cambrian
9
Mesozoic
8
Ordovician
7
Devonian
4
Triassic
4
1979
2
Civil War, 1861-1865
2
Holocene
2
Miocene
2
Mississippian
2
Oligocene
2
Pleistocene
2
Silurian
2
1815-1871
1
1871-1918
1
1918-1945
1
1933-1945
1
1963
1
1964
1
1970
1
1971
1
1979-
1
20th century
1
800-1444
1
Pliocene
1
Pre-Cenozoic
1
Pre-Quaternary
1
Proterozoic
1
To 146 B.C.
1
War of 1812
1