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“Bite-Size Bits of Local, National, and Global History”

Near Branchport in Yates County, New York — The American Northeast (Mid-Atlantic)
 

Bluff Point & Keuka Lake Geology

 
 
Bluff Point & Keuka Lake Geology Marker image. Click for full size.
By William Fischer, Jr., July 30, 2020
1. Bluff Point & Keuka Lake Geology Marker
Inscription.  

The Seabed Became A Plateau
T
he Keuka Lake region belongs to a topographic province called the Allegheny Plateau. The shale and sandstone formations found here represent mud and sand deposits that settled on a shallow sea floor over millions of years. These sediments gradually became rock under the pressure of successive layers in a process called lithification. Many area gorges and glens contain fossils such as trilobites, brachiopods, and corals. Geologically speaking, the surface rocks belong to the West River Group and are sandstones, siltstones, and shales originating from the erosion of the Acadian Mountains to the east. These mountains were a product of the collision of the North American and Avalonian Plates. The region first became dry land more than 300 million years ago during late Devonian times. A long period of uplift and erosion began. During this time, about one vertical mile of rock material was eroded from the original two-mile-thick stack by a system of rivers that developed in the area. One such river occupied the Keuka valley.

Glaciers Covered The Area
T
he Ice Age or

Bluff Point & Keuka Lake Geology Marker image. Click for full size.
By William Fischer, Jr., July 30, 2020
2. Bluff Point & Keuka Lake Geology Marker
Distant marker
Pleistocene Period began about two million years ago, bringing a succession of glacial ice sheets from the north. Evidence has been found indicating there were at least 10 and possibly 20 distinct cold periods that could have resulted in an ice sheet advance and subsequent melt-off. Each glacier scoured the landscape under enormous weight and removed rock material, erasing evidence of the preceding glacier.

The continental ice sheets slowly flowed into existing river valleys as valley glaciers, massively reshaping the topography. The valleys running north-south were greatly deepened and changed from a V-shaped cross-section to a U-shaped one by the south-flowing ice. As the advancing ice sheet thickened, ridges between the glacially deepened valleys were sculpted by the flowing ice into steamlined forms as seen in the ridges between the east and west branches of Keuka Lake. The last continental glacier was at least one mile thick.

The Bluff Was An Island
A
s the last glacier slowly melted and retreated northward, it stalled about 17,000 years ago for a period of time and dumped what has been called the Valley Heads Moraine. This formed a barrier preventing southward drainage of glacial meltwaters. A part of this barrier remains today as the hilly topography between Hammondsport and Bath.

Around 15,000 years ago the water level in the Keuka valley

West Branch of Keuka Lake image. Click for full size.
By William Fischer, Jr., July 30, 2020
3. West Branch of Keuka Lake
Looking south
rose to about 1,000 feet above sea level, causing an overlow of the west branch into the east branch. As water flowed between the present day Keuka Lake State Park and Route 54A, the Bluff became an island for about 300 years. Meanwhile, meltwater continued to flow over the ridge from Keuka Lake to Seneca Lake, eventually forming the present outlet between them. Keuka's level gradually lowered to its present elevation of approximately 714 feet above sea level.

The Finger Lake That Is A "Y"
W
hen underlying shale layers were eroded, harder sandstone on the Bluff's crest resisted. As ancient rivers flowed around the Bluff, it remained, creating today's "Y" shape. Major inlets to Keuka Lake are located at Hammondsport and Branchport. The outlet is in Penn Yan, where the lake level is regulated by a set of gates. From this outlet, water drains to Seneca Lake and then northward through the Seneca-Oswego-Oneida Rivers Drainage Basin, eventually reaching the Atlantic Ocean via Lake Ontario and the St. Lawrence River.

The highest points in the Town of Jerusalem are on the Bluff and the Pinnacle (the hill behind you), each about 1,400 feet above sea level. There are spectacular views from Esperanza Road and along Skyline Drive.

[Illustration captions, clockwise from top center, read]
• Glaciers followed existing streambeds leaving Keuka as

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a "Y"-shaped lake as they receded. (Black lines show where the southern edge of the last receding glacier was 17,000 years ago.) About 15,000 years ago, the water rose so high that the Bluff became an island for about 300 years.

• The east, west, and south branches of Keuka Lake embrace the Bluff.

• The force of water and glaciers contributed to the formation of gullies and glens found around Keuka Lake.

• Keuka Lake Watershed [bottom left, and] Finger Lakes Watershed [immediately adjacent to right]
 
Erected by Bluff Point Association.
 
Topics. This historical marker is listed in this topic list: Natural Features.
 
Location. 42° 35.693′ N, 77° 8.228′ W. Marker is near Branchport, New York, in Yates County. Marker is on New York State Route 54 west of Esperanza Road, on the right when traveling east. Marker is at the roadside pullout. Touch for map. Marker is in this post office area: Branchport NY 14418, United States of America. Touch for directions.
 
Other nearby markers. At least 8 other markers are within 3 miles of this marker, measured as the crow flies. Bluff Point & Keuka Lake History (here, next to this marker); Beddoe Tract (within shouting distance of this marker); "Ahweyneyoun" (Ah-Wey-Ne-Youn) (approx. ¾ mile away); Veterans Memorial (approx. ¾ mile away); Trolley Depot (approx. 0.8 miles away);

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Red Jacket (approx. 0.8 miles away); St. Luke's Episcopal Church (approx. 0.8 miles away); Ball Hall (approx. 2.7 miles away). Touch for a list and map of all markers in Branchport.
 
 
Credits. This page was last revised on August 3, 2020. It was originally submitted on August 3, 2020, by William Fischer, Jr. of Scranton, Pennsylvania. This page has been viewed 61 times since then. Photos:   1, 2, 3. submitted on August 3, 2020, by William Fischer, Jr. of Scranton, Pennsylvania.
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Oct. 24, 2020