Friday, December 17, 2010

What a Geologist Sees - Part 23 [Original Post Date 10/10/08]

Providence Canyons, locally called "the Little Grand Canyon", in Stewart County, Georgia, provides a stark look at what can happen when erosion takes hold in an area underlain by a soft sand.

The canyons are generally on the order of 125 feet deep and are only perhaps 150 years old.

The supposed genesis of the canyons was due to rain running off the corner of a church and beginning a small gully. The surface of this area is locally covered by the residuum of the Paleocene-aged Clayton Limestone, which has been reduced to a iron-rich, reddish clay. One this clay veneer is breached by a gully, the underlying soft, deltaic sands of the Cretaceous Providence Sand. There is essentially nothing to stop the downward erosion or the widening of side canyons. At some point in the future, the area will probably reach some sort of equilibrium as a series of low sandy hills, separated by sand-clogged, braided streams.

As an aside, exposures of sand such as this serve as "recharge zones" for sand aquifers and elsewhere, the subsurface Providence Sand does serve as an aquifer.

[Older posts in this series, before Part 22, are linked here.]

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