Era
Cretaceous
31
From 65 to 140 million years ago
29
20th century
24
19th century
23
From 230 to 280 million years ago
10
Permian
10
1800-1899
9
1839-1876
9
1900-1999
9
Precambrian
8
From 570 million to 5 billion years ago
6
Mississippian
6
Proterozoic
6
1876-1877
5
1876
4
From 570 million to 2 billion years ago
4
1839-1925
3
Cenozoic
3
Civil War, 1861-1865
3
From 140 to 190 million years ago
3
From 2 million years ago
3
From 310 to 345 million years ago
3
From 65 million years ago
3
Jurassic
3
Quaternary
3
Tertiary
3
1823-1867
2
1834-1918
2
1858-1919
2
1880-1954
2
1913-1999
2
1939-
2
1951-1960
2
1956-
2
1958-
2
1967-
2
From 280 to 345 million years ago
2
Indian occupation, 1973
2
Paleocene
2
Paleozoic
2
Pennsylvanian
2
To 1951
2
To 1999
2
(1842?-1877)
1
-1864
1
1564-1616
1
1799-1868
1
1800 - 1899
1
1800 - 1999
1
1800-1999
1
more ...