This map shows the region in Maryland, Pennsylvania, and Delaware where ultramafic bedrock occurs. The ultramafic bedrock that occurs in this region was once part of the ocean floor and was uplifted when a collision of the North American and African Oceanic plates collided 450 million years ago. Ultramafic rock alters to serpentinite when exposed to water and low temperatures. Serpentinite, named for its greenish appearance, give the serpentine barrens its unique soil characteristics. Located within this region is the Baltimore Mafic Complex, a large exposure of ultramafic rock in Maryland and Southeastern Pennsylvania. *This map was made for educational purposes and is not recognized as an official map of ultramafic bedrock. Locations are not exact.*