Era
Cretaceous
84
Quaternary
71
Paleozoic
30
Precambrian
27
Jurassic
25
Cenozoic
22
Tertiary
21
Eocene
16
Pre-Quaternary
15
Pennsylvanian
14
Mesozoic
13
Paleocene
12
Civil War, 1861-1865
11
Cambrian
9
Permian
9
Ordovician
7
Devonian
5
Pleistocene
5
Silurian
5
19th century
4
20th century
4
Triassic
4
Partition, 1995
3
1831-1897
2
1866-1895
2
1945-
2
1979
2
1979-
2
Holocene
2
Miocene
2
Mississippian
2
Oligocene
2
Proterozoic
2
Revolution, 1775-1783
2
1485-1547
1
1596-1673
1
1770-1838
1
1774-1809
1
17th century
1
1815-1871
1
1862-1865
1
1862-1877
1
1871-1918
1
1913
1
1918-1945
1
1930-2006
1
1933-1945
1
1945-1989
1
1945-1992
1
1947-
1
more ...