The Letchworth Gorge is a 22 mile section between Portageville and Mt. Morris. In the Park sometimes known as the "Grand Canyon of the East" (Figure ) there are 3 waterfalls, Upper, Middle and Lower.
The Upper falls are 71 feet high and capped with 28 feet of sandstone from the Nunda formation. Under the Nunda formation are the Gardeau sandstones and shales. Behind the Upper falls is the portage railroad bridge. The old bed of the Genesee valley canal is visible on the East wall. This abandoned canal linked the Erie canal and the Allegheny river.
The Middle falls are .5 miles down stream from the Upper falls. They are 107 feet high and capped with the Gardeau sandstone. 500 feet downstream from the Middle falls there is a landslide formed from unconsolidated glacial till. This till fills a pre-Wisconsin river valley that is now cross-cut by the Genesee river. To the North of the landslide canal builders attempted to tunnel through the bedrock. The drilling failed due to rock cave ins.
The Lower falls are 70 feet high. To the East of the foot bridge over the gorge is a large flat rock called Table Rock. The rock was exposed before the gorge was excavated. Look for the large ripple marks on the surface of the rock.
All three falls have the same discharge and the caprocks have the same resistance so (the three falls should have retreated synchronously). Van Diver suggests that the three falls were formed during three different glacial lake levels. A glacial meltwaler stream may have flowed over a scarp into the lake. The scarp would recede, but erode no deeper than the base level provided by the lake. When the lake level dropped suddenly a new outlet formed. Then a new scarp would form and recede at the same speed as the first. The process would repeat itself to form the three falls.
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