The James River Park System - Richmond, VA

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South Geology Tour

Stop 3b: The Geologic Scar

Digging Deeper

Consider This

The earth’s surface is divided into TECTONIC PLATES [15-200 km (9-124 mi) thick] which are comprised of the continental crust, the oceanic crust, and the upper MANTLE.

Tectonic plates are constantly moving and when they bump together or slide past one another, they cause earthquakes.

Notice the exposed bedrock in the river valley. This rock is PETERSBURG GRANITE, first identified in Petersburg, Virginia. It is the geological scar that resulted from the collision ~330 MYA of two ancient land masses now called North America and Africa. This band of rock runs along the East Coast from New Jersey to Alabama. Where it is exposed by the river, it is called the FALL ZONE.

The Fall Zone

The Fall Zone of the James stretches 11.3 km (7 mi) from Bosher Dam to the Mayo Bridge. It declines steeply from west to east, causing the river to drop 32m (105 ft). Half of that drop is in the last mile. Where the Fall Zone ends, the river flattens. It becomes tidal and travels 160 km (100 mi) to the Chesapeake Bay.

Fall Zone Chart -- see paragraph above for description

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