At the place where two geophysical provinces intersect, the Fall Line attracted Native American settlement, served as a natural crossing point for Hernando DeSoto's journey, and made the Augusta Canal possible. The roar of water over the ledges of Bull Sluice—the turbulent mid-river channel just below the dam—signals the beginning of the Fall Line. Along this four mile zone, the Savannah River drops markedly in elevation as it leaves the hard, crystalline strata of the Piedmont Plateau and hits the softer sedimentary bedrock of the Upper Coastal Plain. The rock ledges form a natural constraint limiting boat travel up the Savannah River from the sea. General James Edward Oglethorpe, founder of Georgia, recognized the defense and trade advantages of controlling the head of navigation, and established Fort Augusta just seven miles downstream of this location in 1736. The 52' drop in water elevation between the upper river and the settled area downstream prompted businessman Henry Cumming to visualize a canal, built in 1845 and enlarged in 1875, to provide transportation, power, and water supply for the city of Augusta, fueling its economic growth. The headgates are designed to regulate the amount of water flowing from the river into the canal. The new 1875 headgates facility incorporated rack and pinion gearing which allowed a single gatekeeper to easily raise and lower seventeen gates. The new 1875 lock was designed with miter gates that swung open to the sides, replacing the low overhead dropgates in the earlier lock, and enabling vessels of any height to pass through the new lock.