Piedmont province - The Geology of Virginia
F O R   S T U D E N T S   &   T E A C H E R S

Generalized Geologic Map of the Virginia Piedmont and Blue Ridge

T

he Piedmont is the largest province in Virginia. To its east is the Fall Zone, which separates the province from the Coastal Plain, and to its west are the mountains of the Blue Ridge province. The Piedmont has gently rolling hills, deeply weathered bedrock, and very little solid rock at the surface. Most rocks at the surface become weathered in the humid climate and buried under a blanket of "rotten rock", called saprolite several meters thick. Most places where you can find outcrops of solid rock are usually in stream valleys where the saprolite has been removed by erosion. The land becomes more hilly the closer you get to the Blue Ridge.

Many igneous and metamorphic rocks make up the bedrock of the Piedmont A. Most of these rocks range in age from the late Pre-Cambrian to Paleozoic and further west make-up the insides of the ancient Appalachian mountains. Triassic sedimentary and igneous rocks can be found in many rock basins B that formed when (what today is) Africa and North America ripped apart to create the Atlantic Ocean 245 million years ago.


Montpelier anorthosite exposed
in the Virginia Piedmont

Many of the rocks in the Piedmont have a complex geologic history, and some may have formed in areas outside of North America. Geologic terranes are groups of rock with very different pasts and are separated from one another by faults. The oldest rocks are ~1100 million years old, and can be found just west of Richmond in a place called the Goochland terrane. Rocks of the Goochland terrane are similar to Pre-Cambrian-age rocks in the Blue Ridge province. Other terranes include Cambrian-Ordovican igneous rocks that are thought to be what's left of an ancient volcanic arc (like the present-day Aleutian Islands in Alaska) that collided with and stuck to the eastern edge of North America. Granitic rocks of Paleozoic age are common, and also formed during this time. Many of the terranes became changed by when the volcanic arc smashed into Virginia, making alot of problems when scientists try to figure out what happened.

Valuable economic resources in the Piedmont province include high quality slate in the late Ordovician Arvonia Formation.