~ ROCHESTER'S HISTORY ~
AN ILLUSTRATED TIMELINE
Many millions of years ago this entire area was covered by a warm,
shallow inland sea.
The chain of Taconic mountains grow and erode away leaving red shale
and sandstone. Traces of these rocks can be seen at the bottom of the gorge
below the Lower Falls. Other mountains develop and erode away leaving more
shales and limestone, also visible in the river gorge.
About a million years ago the earth cooled dramatically and the first
of the great Ice Ages takes over. Four times the polar ice has advanced
over this area, covering Rochester with glacial ice up to two miles thick.
The glaciers in this area did not gouge the surface away as mountain glaciers
do, they worked more like sandpaper rounding and smoothing the contours.
The primary change was actually in the material they left behind. Vast
areas in Canada were scraped down to bedrock and this dirt was pushed south
giving some areas of the Genesee Valley a covering of glacial till 300
Today's geography would be very different had the glaciers not
made their appearance. There would be several deep valleys with ridges
separating them. The many ridges and rounded hills would not be present.
The lakes would never have formed by the normal action of erosion. The
soil would be poor.
245 to 2 MILLIONS OF YEARS AGO
(Mesozoic and Cenozoic Eras)
Area was rich in plant life, first with ferns, mosses, and conifers,
then evolving to flowering plants, forest trees and palms.
Animal life would include massive amphibians, and then the giant reptiles
of the land and air.
This region may have been home to early horses, camels, rhinoceros
and other animals that were driven off by the advancing glaciers.
In the last million years there have been four glacial ages that have
covered the area. Each age scraped and gouged, and sometimes buried evidence
of the previous glaciers. The earliest glacier to leave evidence in the
area arrived here 100,000 years ago. It was about 2,000 miles in diameter,
and 1,000 to 10,000 feet high. This ice would have put about a ton of pressure
on each square inch of the ground below. At the end of its 40,000 year
stay it had compressed the earth below by as much as 2,500 feet! Before
the ice would finally melt away, it would advance and recede across Rochester
five times. Each time scraping away old soil and depositing new. The glacial
till (soil left by the glaciers) in the Genesee Valley is between 200 to
300 feet deep.
Genesee River gradually evolves through erosion of the region.
The Genesee River starts as a spring (today, on the farm of Dave Slaybaugh,
in Gold, PA). About five miles north of Avon the river turns east at Rush
taking the route of Honeoye Creek, until just before Honeoye Falls, where
it turned northward again following the Irondequoit Valley where it joined
the Ontario River at a location near the center of today's Lake Ontario.
The Genesee and the Nile, are the world's only major rivers that flow
12,000 YEARS AGO
Mammoth and Mastodon live in western New York
Retreating glacial ice heads northward, finds new strength and readvances
to the south, then stalls. Melting ice at this static point slopes to the
north at an angle of 20 to 30 degrees. The meltwater along this front,
deposits mounds of debris forming the Pinnacle Range, a range of hills
extending four miles, forming Cobb's Hill, Pinnacle Hill (the tallest at
230 feet), the hills of Highland Park, Mt. Hope Cemetery and the University
of Rochester River Campus.
They are described as a recessional kame moraine. This means that the hills
were not formed by the furthest advance of the glacier, but by the melt
water carrying sand and/or gravel off the ice and depositing it in well
sorted deposits. There are also deposits of glacial till spread over this
area. This means that after the range was formed the glacier advanced again,
covering the area with ice. This last glacial appearance must have been
a weak effort, because it did not scrape the hills away, mearly flowed
over top of them. The exit of the ice sheet wasn't a retreat of the ice
mass as in the past, but just the melting away of the ice, which droped
the well mixed debris trapped in the ice (glacial till) to the ground.
The river channel between Rush and Honeoye Falls is filled by glacial
debris (the Portageville Moraine). Lake Scottsville (elev. 540 feet) is
formed along the present river route, with the Pinnacle Range damming the
northern exit. Water flow continued northward through a depression in the
hills at the University of Rochester, where it joined Lake Dawson (elev.
480 feet) about a mile north of the rapids that were created when the river
crossed the Niagara Escarpment.
Evidence of how important the glacial action has been to this area
as we know it, is all around us. It is easily seen in the fertile soil,
The Great Lakes, and the Finger Lakes. Consider this more subtle, yet profound
example: Had the Pinnacle Range at the University of Rochester been 20
feet higher, Lake Scottsville would not have broken through there. The
debris that had blocked the channel near Avon was at a lower elevation,
and would have become the new outlet. The running water would easily wash
away the blockage, re-opening the river's original, gradual course to Irondequoit
Bay. The Genesee River would not have found its new, more direct
course northward. There would be no falls for early settlers to use for
power, and here would be no Rochester.
Retreating ice exposes a new outlet, and Lake Dawson's level rapidly
drops 45 feet, creating Lake Iroquois (elev. 435 feet). This in turn drains
Lake Scottsville, and moves the mouth of the Genesee a mile further north,
to a point just north of the Veteran's Memorial Bridge. Rapids at the Niagara
Escarpment have eroded to form a 40 foot falls, just north of today's High
Falls. Two new sets of rapids are formed between the escarpment and the
Lake Iroquois remained long enough, so that it's shoreline can still
be seen. Extending 150 miles from Sodus to Lewiston it forms a ridge that
the Indians would follow as a primary east-west trail. Stagecoach lines
follow it from 1818 to 1848. Today's NY Route 104, or Ridge Road follows
this same geologic formation.
Ice clears the Thousand Island Outlet, and the water level drops again
forming Admiralty Lake (elev. 50 feet). The ground in this area has been
so compressed by the absolutely massive weight of the two mile thick ice
sheet, that the lake level is 200 feet lower than today's Lake Ontario.
The Genesee River has to extend it's length by seven miles to reach the
The two lower sets of rapids become the Middle and Lower Falls, moving
southward in the process. The lower gorge south of Stutson Street is carved
The Genesee River drops about 220', over three falls within the Rochester
Land slowly rebounds from glacial weight. (Imagine squeezing a rubber
ball, when you release the pressure it returns to it's original shape.)Because
more weight was removed from the Canadian side of the lake, it is raising
faster. Even though the land has risen 250 feet in Rochester, northern
portions of the lake have rebounded nearly 500 feet. The faster rebound
on the Canadian side is causing Lake Ontario is literaly spill onto New
York, forming the many ponds and the wetlands along the lake shore. The
original outlet of the river has also flooded, forming Irondequoit Bay.
The the lower gorge along the river's new course is flooded to the Lower
When the glaciers finally left the area they left behind many signature
deposits and features. Debris includes random pockets of material ranging
the size of sand, to an Irondequoit field that originally was covered
with 30 to 80 ton boulders. These 'erratic' were taken from northern Canada
by the advancing ice. Melt water from the glaciers formed rivers, on and
in the ice. Debris and gravel would collect along the beds of these rivers
and when the glacier finally melts, this debris is dropped to the earth
forming long snake-like piles called eskers. There is a very impressive
esker in Mt. Hope Cemetery. Mendon Ponds Park also has many notable
glacial features including kettles which are large circular depressions
in the ground formed when huge chunks of ice, buried in the ground melt
Pinnacle Hill is the highest point in Rochester at 749'.
The Erie Canal crosses the city at 508' above sea level.
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