Rivers and Lakes of the Rochester Area

by Charles F. Wray


The Rochester region has been favored with several unique geologic features, and its rivers and lakes are no exception. The combination of 24 parallel north-south river valleys and the effects of a massive continental glacier have given us a series of lakes, river cataracts, and steep-walled canyons that cannot be equaled anywhere in the world. We have some of the largest freshwater lakes in the world, some of the most beautiful lake and hill scenery to be found anywhere, and one of the few major north-flowing rivers in North America. This north-flowing river, the Genesee, is the only stream to completely cross the State of New York.

To understand the origin of our lakes and rivers, we must go back to pre-glacial times to see what our part of the world looked like. None of us would be able to recognize our Genesee Country in those waning centuries before the great continental ice sheet reached here. There apparently were no lakes, no waterfalls, nor any steep-sided canyons. The area was in advanced old age, erosionally speaking. Millions of years of erosion had cut the land surface down and rivers had carved deep parallel north-south valleys across central and western New York. Most of these rivers flowed northward into a great east-west valley containing a major river. This river, the Ontarian, is believed to have flowed westward through the middle of present Lake Ontario to the Mississippi basin.

Our pre-glacial Genesee River followed much of its present course from Genesee, Pennsylvania, northward through Wellsville, Belmont, to Portageville, New York. Near Portageville our preglacial river turned eastward through Nunda and joined the larger Dansville River near Sonyea in the present valley of the Canaseraga. From here, the Dansville-Genesee River flowed northward past Geneseo to Avon. Four miles north of Avon, the river encountered the relatively soft Salina Shales. The river turned eastward following the strike of these beds, along the present course of Honeoye Creek, through the town of Rush, and then northward again near Fishers. From Fishers the pre-glacial river followed the present course of Irondequoit Creek to our present Irondequoit Bay and then continued northward down the south side of the Ontarian River Valley into the Ontarian River.

Such was the picture at the beginning of the Ice Age. The 8,000 feet of sediments that had accumulated during the 325 million years that this area was under the ocean had been gradually raised above sea level and had been eroded by the winds and rains of 200 million years. Then, approximately 1 million or more years ago, this region was carved by the successive advances and retreats of the Laurentian Ice Sheet--a mile-high continental ice cap. This mass of ice flowed to the Rochester region from east of Hudson Bay, and was squeezed into the north-south river valleys under unbelievable pressure. The ice flowed through these valleys at accelerated speeds with consequently greatly increased erosional abilities. It plucked out rocks and scoured these valleys to depths that ranged to below sea-level.

About 20,000 years ago, when the last advance of the ice was melting back, the post-glacial rivers found themselves impounded by the damming effect of the ice front and by the moraines built up by the ice cap. Some of their former valleys, especially their east-west sections, had been filled in with glacial drift. Many of their north-south valleys had been deepened and enlarged.

As lower outlet channels were uncovered by the retreating ice, the lakes formed by the impounded rivers and the melting ice gushed out to lower levels, leaving the many terraces seen on our hill and valleys sides today. At Portageville, our post-glacial Genesee found its eastward trending valley plugged with glacial drift and moraines, and was forced to flow northward over a series of alternately hard and soft rock layers of the Upper Devonian strata.

The Genesee was reinforced by the waters from the melting ice and with this mighty volume cut the largest and deepest canyon east of the Mississippi River. In cutting this canyon, the Genesee plunged over the more resistant rock layers, forming the beautiful waterfalls and rapids that bring thousands of visitors every year to Letchworth Park. (Fig. 7) & (Fig. 8)

At Mount Morris, the Genesee broke back into its mature, pre-glacial valley, and continued northward to a point four miles north of Avon (Golah, just to the west of West Rush). Here the Genesee again found its eastward-trending valley plugged tight with glacial drift. Once again, it was forced to look for a new route, and continued on northward cutting a new channel through present Rochester and joining Lake Ontario's predecessor, Lake Iroquois, near the Veterans' Memorial Bridge. At Rochester it again flowed over a series of alternately hard and soft rock layers of Lower Silurian strata and cut a second impressive canyon with three cataracts.

The Genesee River, in pre-lake Ontario time (Lake Iroquois), formed a large delta of finely bedded clay, silt, and sand that covers most of the area north of Ridge Road, east of the present Genesee and bordering on Irondequoit Bay. The prevailing easterly currents of Lake Iroquois carried these river silts from the east mouth of the Genesee to its pre-glacial channel in Irondequoit Bay.

The Genesee was named by the Seneca Indians. They called it "Ge-ne-see," its literal translation meaning "pleasant banks". It was first heard of by Europeans in 1534, when the Indians told Jacques Cartier of its existence. The first white man to see it was Etienne Brule, the intrepid Courier-duBois and interpreter for Samuel de Champlain. He crossed the Genesee in 1615 while on one of his many errands for Champlain.

The Genesee is born in a pasture from a gentle hillside spring in Potter County, Pennsylvania, near the town of Gold. It starts out at an elevation of 2,500 feet on the Allegany Plateau, trickles rapidly down hill till it joins two other members of its family in the town of Genesee, Pennsylvania. From Genesee, it is only a few miles to the New York State border, and Allegany County. The Genesee River crosses the structure of southern Allegany County at nearly right angles. The underlying folded rocks are shales and sandstones of Devonian age.

The Genesee meanders relentlessly down its well-worn valley from an elevation of 1,610 feet at the Pennsylvania border with a grade of about 10 feet per mile. It leaps over six cataracts, three in Letchworth State Park, and three in the City of Rochester. It ends its short but eventful life by peacefully joining Lake Ontario at an elevation of 246 feet above sea level. The Genesee's main tributaries are Black Creek, Honeoye Creek, Canaseraga Creek, and Wiscoy Creek.

The Genesee with its falls was and still is an important source of water power. The river was the sole reason for the beginning of the City of Rochester. Without the Genesee, there would be no Rochester. Early Rochester grew up as the milling and flour center of the young United States. The broad and fertile flood plains of the Genesee south of Rochester grew much of our young nation's wheat. Later, when our country moved westward, Rochester was replaced by Minneapolis as the "Flour" city. Rochester, with its many parks, then changed its name to the "Flower" city.

The Finger Lakes

The 24 parallel north-south river valleys carved by the pre-glacial rivers of Central and Western New York were greatly modified by the continental ice sheet resulting in the beautiful Finger Lakes Country. The Finger Lakes have been studied by many well-known geologists. Their studies have resulted in the separation of the lakes into an eastern and a western group.

The eastern group--Otisco, Skaneateles, Owasco, Cayuga, and Seneca-were formed by north-flowing rivers that had their headwaters on the Portage Escarpment. The western group-Keuka, Canandaigua, Honeoye, Canadice, Hemlock, and Conesus--were formed by south-flowing rivers. Canandaigua is believed to be the headwaters of the Dansville River. All the remaining, with the exception of Keuka (fig. 9), are believed to have been tributaries of the Dansville River. Keuka or "crooked lake" is probably the most obvious proof of the southerly flow of these preglacial rivers. The two arms of this Y-shaped lake come together at an acute angle to form the larger and deeper valley to the south.

We have already mentioned how the ice from the continental ice sheet was funneled into and forced through these river valleys. The eastern group, with the barrier Portage Escarpment at its south end, was scoured down to great depths, Seneca to 174 feet below sea level and Cayuga to 34 feet below sea level. Small tributary streams cascade into these lakes down steep-sided ravines and over beautiful waterfalls. One of these, Taughannock Falls (fig. 4), drops 215 feet. It is 55 feet higher than Niagara Falls and one of the highest east of the Rocky Mountains. The western group of lakes was not scoured nearly as deep, presumably because of their southerly flow and lack of constriction at their south end.

Just why we have lakes in eleven of the 24 valleys is best explained by the affects of the glacier. The ice blocked some of the south ends of these valleys with glacial debris and terminal moraines. During the ice age, the land surface was depressed by the tremendous weight of the ice. Since the end of the ice age, the land surface has been gradually rising. It apparently is still rising with the center of this uplift in the region of the St. Lawrence River Valley. Proof of this can be found by following the shoreline of Lake Iroquois on present Ridge Road eastward from Rochester. The elevation of this beach will be found to increase as we go eastward and northward.

Our Finger Lakes were formed by the trapping of water in these deepened valleys, between glacial debris at the south end of these lakes and the rising ground to the north. One small lake exists west of the Genesee Valley. Silver Lake is not normally considered as one of the Finger Lakes, mainly due to its separation from the other lakes, nevertheless it was formed by the same chain of events that formed the other Finger Lakes.

The Great Lakes

Our Great Lakes, the largest bodies of fresh water in the world, owe their existence to a syncline that filled with relatively soft ocean sediments. These sandstones, shales, and limestones were worn down into deep river valleys during the millions of years of erosion preceding the ice age. As in the case of the Finger Lakes, the Great Lakes were scoured and deepened by the great ice sheet. The northern boundary of the lakes was established by the hard crystalline Precambrian rocks of the Canadian Shield. Their eastern and southern edges were formed by the rocks of the Middle Silurian Niagaran Series (the Lockport Escarpment in our area).

The Great Lakes extend half way across the continent of North America, some 2,000 miles from the Atlantic. Lake Superior, the northernmost and the westernmost is the largest body of fresh water in the world. It has a surface elevation of 602 feet and a maximum depth of 1302 feet (700 feet below sea level).

Even though our own Lake Ontario is the smallest of the Great Lakes, it is the 14th largest fresh-water lake in the world. It is the third deepest of the Great Lakes, having a maximum depth of 778 feet (532 feet below sea level). It discharges 234.500 cubic feet of water per second into the St. Lawrence River. Ontario's main source of water is shallow Lake Erie, whose water flows through the Niagara River, over Niagara Falls, and into Lake Ontario.

The Great Lakes are fairly stable, having a maximum seasonal water level change of only 6f feet. This was not always the case as there is evidence of both higher and much lower levels (400 feet) in the past.

The Great Lakes hold a nearly inexhaustible supply of fresh water for us if we can keep from polluting them. Transportation wise, they make possible cheap inland shipping and a direct oceangoing shipping route from the Atlantic to the middle of our continent. Its existence has done much to create an industrial empire around its boundaries.

Our climate is directly affected by the presence of the Great Lakes. During the summer, their waters absorb the heat and during the winter this stored heat is dissipated into the air tempering the climate. This has made possible the extensive fruit belts around the lakes. It is also responsible for local snow belts especially at the east ends of the lakes.

Early Man In Western New York

Not much is known of the pre-glacial fauna and flora of Western New York. There most certainly must have been a heavy cover of vegetation and associated animal life. We do know that at the close of the glacial period, man made his first appearance in these parts. About the time of the Valders Advance -- the very last minor advance of the ice in the northern part of the Great Lakes -- Paleo-Indians, the early big game hunters, penetrated the forests of Central and Western New York. They probably came here in pursuit of the ice age elephants, the mastodon and the mammoth.

Mastodons were fairly numerous in Western New York, as indicated by the more than 50 individual finds that have been made in Western New York. Apparently mammoths were not so numerous as only a few have been found in this area. We can be certain that early man was here from the sporadic discovery of his characteristic fluted (Clovis) and lozenge-shaped points. None of his points has as yet been found associated with either mastodon or mammoth bones in New York State although they have been found with mammoth bones in our southwest.

Radiocarbon dates have reasonably well established the end of the ice age in this area as about 8 to 10 thousand years ago. Man may be assumed to have first come here about 7,000 years ago. Only a few small camp sites of these Paleo-lndians have been found in New York State.

The first permanent Indian settlements in this area were made by the Early Archaic about 5,000 years ago. Villages of these early pre-ceramic and pre-agricultural culture are found on the shores of the Finger Lakes and along the terraces of the Genesee River south of Rochester.


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