Enter part of unit name, click search for matches, then click add to select desired geologic unit.

Quaternary Tertiary Cretaceous Permian Pennsylvanian Upper Pennsylvanian Middle Pennsylvanian Lower Pennsylvanian Upper Mississippian Lower Mississippian Upper Devonian Middle Devonian Lower Devonian Middle Silurian Lower Silurian Upper Ordovician Middle Ordovician