The Gettysburg Formation is a mapped bedrock unit consisting primarily of sandstones, conglomerates, and shales.

[2] The Gettysburg Formation and other formations of the Newark Supergroup were deposited in the Gettysburg Basin, just one of many Triassic rift basins existing on the east coast of North and South America, which formed as plate tectonics pulled apart Pangaea into the continents we see today.

The conglomerates within the formation were most likely alluvial fan or mudflow deposits, or possibly talus, eroding directly from the Precambrian and early Paleozoic rocks to the north and south.

Relative age dating of the Gettysburg Formation places it in the Late Triassic period.

In 1977, B. Cornet dated a basalt flow near Aspers, Pennsylvania and led to his conclusion that the Gettysburg is of late Carnian and Norian to Early Jurassic age.