In October 1861 , the Confederates constructed Building batteries at Evansport ( now downtown Quantico , consisted of two batteries on the river bank , and another inland ) , a CSA field battery located at the mouth of Chopawamsic Creek where it empties to the Potomac ( now the Marine Corps Air Facility ) , Shipping Point ( now Hospital Point on Quantico , number of guns unknown ) , Freestone Point ( a CSA four-gun battery on the shore of the Potomac River , now within Leesylvania State Park ) , and Cockpit Point ( near the current asphalt plant , consisted of six guns ( one heavy gun ) in four batteries , a powder magazine , and rear rifle pits , on top of a high cliff known as Possum Nose ) .