When the English colonists were first exploring Virginia, they quickly explored up the rivers as far as their ships could float. In 1607, Christopher Newport sailed up the James River to the location of what is now Richmond, before returning to England and reporting on his success at delivering 104 colonists to a new settlement called Jamestown.
A year after unpacking the Susan Constant, Discovery, and Godspeed and building a fort at Jamestown, the English had sailed or rowed up the James, York, Rappahannock, and Potomac rivers to the line of waterfalls known today as the Fall Line. John Smith reached the current location of Alexandria in 1608 in a small boat known as a shallop.
The waterfalls and rapids of the Fall Line blocked the English from sailing further west into the North American continent, and of course prevented the English from discovering a Northwest Passage permitting ships to sail through Virginia to China.
The Fall Line is the western edge of the Coastal Plain, the physiographic province where tides affect the water level in the rivers and where ocean-going vessels can sail in the Virginia rivers. One indication of the constraint to transportation imposed by the Fall Line: Smith could not get his shallop across Little Falls near the current location of Georgetown, so he did not discover the very distinctive Great Falls further upstream.
The English immigrants to Virginia initially settled east of the Fall Line. They cleared the forest and started plantations in the flat Coastal Plain, close to the Chesapeake Bay and with easy access by ship to Europe and the islands in the Caribbean. Because the Fall Line blocked ships from sailing further west, the English colonists chose to occupy the lands on the Coastal Plain for over 125 years before they moved west up the James, York, Rappahannock, and Potomac rivers into the Piedmont. As a result, the English disrupted and displaced the Algonquian-speaking tribes that lived in Tidewater long before seizing the lands of Native Americans that spoke Siouan or Iroquoian languages.
Settlement west of the Fall Line imposed a substantial transportation burden on the colonists. East of the waterfalls in the Chesapeake Bay watershed, the English could roll heavy hogsheads of tobacco from barns to a wharf and load barrels of "smoking leaf" directly onto ships headed to Europe.
West of the waterfalls, tobacco had to be hauled by wagon on unpaved roads to a river, loaded onto small boats (batteaux), floated to the Fall Line, moved off the small boats onto wagons, carried a few miles on unpaved roads around the waterfalls, then loaded onto ocean-going vessels at the ports below the waterfalls. The extra costs for handling bulky tobacco cut deeply into the profits of colonial farmers living upstream of the Fall Line.
The "head" of water navigation, the rapids at the Fall Line, required captains of ocean-going ships to unload European goods. Where rivers were blocked by a rapid, warehouses were built to store tobacco before export. Imported goods were unloaded from ocean-going ships, and stores developed at the Fall Line. Customers came to the stores, or wagons would be loaded to deliver items to inland plantations. As the population of the Virginia colony increased, warehouses and stores grew and towns - Alexandria, Cochester, Occoquan, Dumfries, Fredericksburg, Richmond, Petersburg, and Emporia - developed at the Fall Line.
Later, canals were built so small boats could bypass the waterfalls, and the water in the canals was tapped for hydropower. Falling water turned wheels, and through mechanical ingenuity the turning wheels were tapped to grind grain, saw wood, and supply mechanical energy for local manufacturing.
In the days before power lines could carry electricity anywhere, factories were built near energy sources. The falling water at the Fall Line was a very attractive energy source. In the first half of the 1800's, Richmond in particular became an industrial powerhouse using waterpower to grind grain and manufacture iron products. People walked to work before the development of the streetcar inthe 1880's, so factories stimulated urban population centers. The Fall Line today is marked by a string of cities stretching from Baltimore, Maryland to Augusta, Georgia.
What if there had been no Fall Line? Instead of a concentration of population in the Chesapeake Bay watershed for over a century, settlers might have rushed westward upstream from Jamestown to fill the James River valley first. That would have brought the colonists into conflict with different Native American tribes that occupied the Piedmont in the 1600's.
Instead, by the time the English moved west into the Piedmont and south into the Shenandoah Valley in the 1720's and 1740's, those tribes had already left. There were conflicts on the borderlands between English and Native Americans in the 1700's, but few of those Native Americans were residents of Virginia. Instead, most fights on the frontier involved Iroquois raiding south from New York or Shawnee raiding eastward from Ohio.
impact of the Fall Line and the Blue Ridge in the colonial settlement of Virginia is reflected in the formation of counties as immigrants moved west
Source: Newman Library - Atlas of Historical County Boundaries
If the Fall Line had been a high range of mountains, and access to international shipping had been too expensive for immigrants that crossed the mountains, perhaps colonial Virginia might have created a diversified farm economy. Colonists might have grown a range of crops that could be processed and used locally - closer to how New England developed in colonial times.
Instead, Virginia colonists on the Piedmont as well as the Coastal Plain emphasized staple production of just one crop, in quantities that could not be consumed locally and had to be sold for export. The colonists created a legal system to support the use of very cheap labor to grow that tobacco. Instead of developing a diversified economy based on small farms, Virginia farmers aspired to grow into plantation owners and supported the system of slavery.