During the past million years there were four glacial ages that covered the Rochester area with the southern edges of the Laurentide Ice Sheet and those advances were major impactors in the formation geology and geography of the area.
The most recent glacier that left evidence here was about 10,000 years ago and it caused compression of the earth by as much as 2,500 feet (760 m).
About 12,000 years ago, the area underwent massive changes, which included the rerouting of the Genesee and other water bodies.
The pre-ice age eastern branch of the Genesee runs south of Mount Morris and was completely diverted by extensive terminal moraines in Livingston County with a key blocking dam just south of Dansville, so most of the upper section of the ancient river was diverted instead to fall the off Appalachian Plateau toward the Susquehanna River system (to an eventual destination well to the southeast).

Currently only a small creek flows in what is left of this large paleogeologic valley.
The area of the lower river was also affected.
 Since the earth rebounded from the melting glaciers more rapidly in Canada than in New York, water from Lake Ontario was spilled over New York due to its lower elevation.
During this time, the original outlet of the Genesee River, Irondequoit Bay, was flooded out, creating the current bay.
 As these waters later retreated, glacial debris caused the river to be rerouted to the west along its current path.

The Seneca nation traditionally lived between the Genesee River and Canandaigua Lake.
The region was surveyed by Thomas Davies in 1766.
The High Falls was then also known as the Great Seneca Falls, and the Genesee River was also spelled Zinochsaa by early writers.

If "not for hydropower, the flour mills, clothing mills, and tool fabricators would not have located in Rochester", and the 1825 Erie Canal allowed the mills to ship products to New York City.
A few hundred feet north of the center of the village of Rochester, the Erie Canal crossed the Genesee River via an 1823 stone aqueduct (802 feet (244 m) long, 17 feet (5.2 m) wide), which was replaced by the Second Genesee Aqueduct in 1842.

Historically, the river's gorge formed a clearly demarcated border between the lands of the Five Nations of the Iroquois, whose range extended east and the related tribes of the Erie people along the west side of the gorge.
By the end of the Beaver Wars and the American Revolution, the lands in all of upstate New York into the Ohio Country were controlled by the Iroquois Confederation, but were also effectively depopulated, the tribes weakened in the Revolution.
In 1779, on the orders of George Washington, the Sullivan Expedition destroyed over 40 Haudenosaunee villages in and around the watershed to force the Seneca and allied nations out of the newly formed United States.
Subsequently, with most Iroquois having fled to Canada, the remnant tribal groups were in no position to further impede white settlers, so most of New York state west of the Genesee River became part of the Holland Purchase after the American Revolution.
From 1801 to 1846 the entire region was sold to individual owners from the Holland Land office in Batavia, New York.
 The river demarcates the "Genesee Country" of New York to the west and the Finger Lakes geographic region, and heartland of the Iroquois to the east.

On Friday, November 13, 1829 (Friday the 13th), the daredevil Sam Patch jumped to his death before 8,000 spectators at the Upper Falls in Rochester.

In 1836 the Genesee Valley Canal was begun to build a new canal from the Erie Canal near Rochester, up the Genesee Valley, across to the Allegheny River at Olean.
 Construction of new sections extended upriver (southward) until 1880.
 Although an important commercial route, the canal was plagued by frequent flood damage and the final leg down the Allegany River was never completed.
 The most difficult section to build was the bypass around the gorge and falls at present day Letchworth Park.
 The canal followed the old Native American portage route, which necessitated many locks.
 The
During the past million years there were four glacial ages that covered the Rochester area with the southern edges of the Laurentide Ice Sheet and those advances were major impactors in the formation geology and geography of the area. The most recent glacier that left evidence here was about 10,000 years ago and it caused compression of the earth by as much as 2,500 feet (760 m). About 12,000 years ago, the area underwent massive changes, which included the rerouting of the Genesee and other water bodies. The pre-ice age eastern branch of the Genesee runs south of Mount Morris and was completely diverted by extensive terminal moraines in Livingston County with a key blocking dam just south of Dansville, so most of the upper section of the ancient river was diverted instead to fall the off Appalachian Plateau toward the Susquehanna River system (to an eventual destination well to the southeast).
Currently only a small creek flows in what is left of this large paleogeologic valley. The area of the lower river was also affected.  Since the earth rebounded from the melting glaciers more rapidly in Canada than in New York, water from Lake Ontario was spilled over New York due to its lower elevation. During this time, the original outlet of the Genesee River, Irondequoit Bay, was flooded out, creating the current bay.  As these waters later retreated, glacial debris caused the river to be rerouted to the west along its current path.
The Seneca nation traditionally lived between the Genesee River and Canandaigua Lake. The region was surveyed by Thomas Davies in 1766. The High Falls was then also known as the Great Seneca Falls, and the Genesee River was also spelled Zinochsaa by early writers.
If "not for hydropower, the flour mills, clothing mills, and tool fabricators would not have located in Rochester", and the 1825 Erie Canal allowed the mills to ship products to New York City. A few hundred feet north of the center of the village of Rochester, the Erie Canal crossed the Genesee River via an 1823 stone aqueduct (802 feet (244 m) long, 17 feet (5.2 m) wide), which was replaced by the Second Genesee Aqueduct in 1842.
Historically, the river's gorge formed a clearly demarcated border between the lands of the Five Nations of the Iroquois, whose range extended east and the related tribes of the Erie people along the west side of the gorge. By the end of the Beaver Wars and the American Revolution, the lands in all of upstate New York into the Ohio Country were controlled by the Iroquois Confederation, but were also effectively depopulated, the tribes weakened in the Revolution. In 1779, on the orders of George Washington, the Sullivan Expedition destroyed over 40 Haudenosaunee villages in and around the watershed to force the Seneca and allied nations out of the newly formed United States. Subsequently, with most Iroquois having fled to Canada, the remnant tribal groups were in no position to further impede white settlers, so most of New York state west of the Genesee River became part of the Holland Purchase after the American Revolution. From 1801 to 1846 the entire region was sold to individual owners from the Holland Land office in Batavia, New York.  The river demarcates the "Genesee Country" of New York to the west and the Finger Lakes geographic region, and heartland of the Iroquois to the east.
On Friday, November 13, 1829 (Friday the 13th), the daredevil Sam Patch jumped to his death before 8,000 spectators at the Upper Falls in Rochester.
In 1836 the Genesee Valley Canal was begun to build a new canal from the Erie Canal near Rochester, up the Genesee Valley, across to the Allegheny River at Olean.  Construction of new sections extended upriver (southward) until 1880.  Although an important commercial route, the canal was plagued by frequent flood damage and the final leg down the Allegany River was never completed.  The most difficult section to build was the bypass around the gorge and falls at present day Letchworth Park.  The canal followed the old Native American portage route, which necessitated many locks.  The
Genesee River