Cretaceous 11
19th century 8
Civil War, 1861-1865 8
Pennsylvanian 8
Quaternary 8
Permian 7
Mesozoic 5
1848-1860 4
20th century 4
Paleozoic 4
Carboniferous 3
Cenozoic 3
Jurassic 3
Precambrian 3
Tertiary 3
21st century 2
Ordovician 2
Revolution, 1775-1783 2
Siege, 1863 2
World War, 1914-1918 2
1608-1674 1
1743-1826 1
1809-1865 1
1834-1902 1
1840-1928 1
1860-1890 1
1865-1898 1
1869-1934 1
1931-1990 1
1931-2022 1
1976-2000 1
Archaean 1
Cambrian 1
Early modern, 1500-1700 1
Guidebooks, 1968 1
Mississippian 1
Pleistocene 1
Proterozoic 1
Roman period, 55 B.C.-449 A.D. 1
Siege, 1781 1
Siege, 1862 1
To 146 B.C. 1
To 1848 1
Triassic 1
War of 1812 1