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A Brief Geological Review of Coos Canyon, Byron, Maine
A tour of the scenic byways of western Maine is not complete without a stop at Coos Canyon, a popular rest stop on State Highway 17 maintained by the Maine Department of Transportation. On a stretch of road designated as a National Scenic Byway, the formidable Coos Canyon was formed by the violent action of the Swift River as it pours from the Western Mountains across the metamorphic units that underlie this area. The waters of the Swift also carry with it flakes of precious metal from a "mother lode" somewhere out in the hills, making this a popular stop with gold panners (223Kb pdf format). As you shake the sawdust of Rumford from your feet on your way to the breathtaking views at the Height of Land, you will not be disappointed during any season with a stop at Coos Canyon.
Geology of the Canyon
From Rumford to Rangeley, this area of western Maine is underlain with a variety of metamorphic rock units ranging in age from around 490 to 400 million years, which are punctured by several bodies of granite and related igneous rocks that are as young as 370 million years old. The high ground to the west of the Swift River in the Byron area is underlain with metamorphic rocks in the contact zone with granite, making the metamorphic rock there particularly resistant to weathering and erosion.
At Coos Canyon, the Swift River cuts through the Perry Mountain Formation of Silurian age (418-443 million years). Named for exposures on Perry Mountain near Rangeley, this unit consists of alternating layers of quartzite and schist, typically in beds a few inches thick. The quartzite layers were originally fairly clean quartz sand, although some beds probably contained some clay minerals as well. The schist was originally silt and mud. Heat and pressure caused by multiple episodes of mountain building transformed these original sedimentary materials to the metamorphic rocks exposed today.
Some features of the rocks at Coos Canyon
The exposures at Coos Canyon display many of the features common to the rocks of the region. Here are some of them:
Moench, R. H. and Hildreth, C. T., 1976, Geologic map of the Rumford quadrangle, Oxford and Franklin Counties, Maine: U.S. Geological Survey, Geological Quadrangle Map GQ-1272, scale 1:62,500.
Text and photos by R. Marvinney
Originally published on the web as the January 2008 Site of the Month.
Last updated on January 25, 2008
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