Era
20th century
113
Tertiary
70
Miocene
63
Cenozoic
58
To 1846
46
Quaternary
38
19th century
36
Cretaceous
34
Pliocene
28
1846-1850
26
Mesozoic
25
Pleistocene
25
Eocene
17
1850-1950
16
21st century
16
Paleozoic
13
1713-1784
10
Devonian
9
Neogene
9
Oligocene
9
Permian
9
1951-
8
Jurassic
8
Civil War, 1861-1865
7
To 1848
7
1947-
6
Triassic
6
1838-1914
5
1927-1993
5
1950-
5
Cambrian
5
Carboniferous
5
Holocene
5
Paleocene
5
Pennsylvanian
5
1902-1968
4
1934-
4
1944-
4
Indian occupation, 1969-1971
4
Ordovician
4
Precambrian
4
1497?-1543
3
1885-1945
3
1888-1953
3
18th century
3
1933-
3
1945-
3
1945-1989
3
1954-
3
1957-
3
more ...