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

Potomac in Montgomery County, Maryland — The American Northeast (Mid-Atlantic)
 

A Geologic Barrier

 
 
A Geologic Barrier Marker image. Click for full size.
By Tom Bosse, July 4, 2020
1. A Geologic Barrier Marker
Inscription.  Canal engineers encountered many problems, but perhaps the most perplexing was navigating around the Great Falls of the Potomac.

At Widewater the canal builders used a river channel abandoned thousands of years ago by the Potomac when it cut its present gorge. At this bend, just above Widewater, the engineers found a steep cliff where the old channel ended, and had to build an immense buttressed wall to cradle the canal and towpath about 70 feet above the present river level.

Before the Ice Age the Potomac flowed at this level where the canal is now and had not yet cut the deep gorge you see below.

As the sea level dropped during the Ice Age, the river cut its channel deeper to reach the lowered sea level.

By about 10,000 B.C. the river had abandoned its old channel at Widewater and cut the new one you see today. Just upstream are the Falls, where sand and gravel carried by the river continue to scour and grind away the ancient bedrock.
 
Erected by Chesapeake and Ohio Canal National Historical Park - National Park Service, U.S. Department of the Interior.

A Geologic Barrier Marker image. Click for full size.
By Tom Bosse, July 4, 2020
2. A Geologic Barrier Marker

 
Topics and series. This historical marker is listed in these topic lists: Parks & Recreational AreasWaterways & Vessels. In addition, it is included in the Chesapeake and Ohio (C&O) Canal series list.
 
Location. 38° 59.902′ N, 77° 14.917′ W. Marker is in Potomac, Maryland, in Montgomery County. Marker is on Chesapeake and Ohio Canal Towpath, on the left when traveling north. Marker is located within the Chesapeake and Ohio Canal National Historical Park. Touch for map. Marker is in this post office area: Potomac MD 20854, United States of America. Touch for directions.
 
Other nearby markers. At least 8 other markers are within walking distance of this marker. Fighting Floods (a few steps from this marker); Creating a National Park (within shouting distance of this marker); Great Falls Tavern (about 700 feet away, measured in a direct line); a different marker also named Great Falls Tavern (about 700 feet away); Washington Aqueduct (approx. 0.2 miles away); Welcome to Great Falls (approx. 0.2 miles away); Olmsted Island (approx. 0.2 miles away); People and the Potomac (approx. 0.3 miles away in Virginia). Touch for a list and map of all markers in Potomac.
 
The Potomac River image. Click for full size.
By Tom Bosse, July 4, 2020
3. The Potomac River
 
 
Credits. This page was last revised on January 12, 2021. It was originally submitted on January 11, 2021, by Tom Bosse of Jefferson City, Tennessee. This page has been viewed 42 times since then. Photos:   1, 2, 3. submitted on January 11, 2021, by Tom Bosse of Jefferson City, Tennessee. • Bill Pfingsten was the editor who published this page.
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Mar. 3, 2021