Era
To 1846
51
Cretaceous
45
Permian
36
Revolution, 1835-1836
35
20th century
27
Civil War, 1861-1865
25
19th century
23
Pennsylvanian
22
1846-1950
17
Republic, 1836-1846
17
Quaternary
12
Tertiary
12
1793-1863
10
Carboniferous
8
21st century
7
Paleozoic
7
1865-1950
6
Eocene
6
1841-1845
5
Cenozoic
5
Precambrian
5
1815-1875
4
1866-1895
4
1959-1993
4
Cambrian
4
Devonian
4
Mesozoic
4
Mississippian
4
1793-1836
3
1821-1861
3
1836-1929
3
1846-1865
3
1851-1878
3
1908-1973
3
1951-
3
Oligocene
3
Triassic
3
Wars of Independence, 1810-1821
3
1800-1874
2
1810-1821
2
1811-1862
2
1817-1899
2
1818-1891
2
18th century
2
1910-
2
1917-1963
2
1979-1997
2
Holocene
2
Jurassic
2
-1987
1
more ...