The Yorktown Formation is a mapped bedrock unit in the Coastal Plain of Maryland, Virginia, North Carolina and South Carolina.

The Yorktown is composed largely of overconsolidated sand and clay with abundant calcareous shells, primarily bivalves.

[3] The uppermost Tunnels Mill Member is recognized in Maryland only.

[5] The age was revised by Gibson (1983) to extend into the Middle Pliocene based on foraminifera.

[6] Further biostratigraphic work with ostracods and foraminifera was completed by Cronin (1991), which also summarized previous investigations.