Veach Gap Anticlines EarthCache
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A short hike leads to a location where hard rock has been bent and folded.
In order to understand the geology of the Massanutten mountain range, it is important to understand a little about plate tectonics. The Alleghenian orogeny that occurred at the end of the Paleozoic era about 250 Million years ago caused the uplift of the Blue Ridge Mountains and the folding and faulting of the ridges and valleys west of the Blue Ridge, including Massanutten Mountain. The Alleghenian orogeny resulted when the African Plate collided with North America, forming the supercontinent of Pangaea. The compression of Shenandoah Valley resulted in the formation of a syncline. A syncline is a geologic formation that results in the strata being concave up such that the youngest rocks are in the center, much like a bowl.
Following the Alleghenian orogeny, the continental plates reversed and Pangaea broke apart to form the Atlantic Ocean and the current location of continents. The U-shaped syncline that formed in the Shenandoah Valley eroded during the following millions of years, removing the softer shales and mudstones in the center, and leaving behind the harder sandstones, quartzites, and granites. The Massanutten sandstone gradually became exposed as older rocks eroded, forming the crest of Massanutten Mountain even though it is younger rock than the rocks in the Fort Valley inside the Massanutten range.
Although it is normally easiest to see the effects of geologic folds from high overlooks or in an airplane because the scale is so large, there are a few places where we can view smaller-scale folds. At the posted coordinates you can observe several examples of Massanutten sandstone that have been deformed producing anticlines. Massanutten sandstone is normally an exceptionally hard rock, however it still bent over time. This area is also unusual because the older rock is found lower or closer to the ground, while most of the Massanutten range has the younger rocks at the highest elevations.
An anticline is a fold that is convex up and has its oldest beds at its core or the inside of the fold. At the posted coordinates you can see a sequence of folded rock layers that are progressively older toward the center of the fold. This small anticline contrasts with the larger synclinal pattern of the Massanutten range as a whole because, as stated earlier, in most cases the Massanutten range exhibits younger rocks at the highest elevations.
The Veach Gap anticlines are about a mile hike from the Veach Gap trailhead. It is an easy hike with several stream crossings. Alternatively, the anticlines can be reached via a much tougher 9 mile hike one way from the Elizabeth Furnace Campground via the Massanutten Trail and Sherman Gap Trail. The coordinates refer to the first anticline, and all anticlines can be viewed from the trail.
To log this find, email answers to the following questions to the cache owner (then you may log the find; I will let you know if anything needs correcting):
1. Why do you suppose geologists term this rock formation an anticline rather than a syncline? You might think the answer has to do with the direction of the folds, but it does not.
2. Speculate on the cause of the folds in these rocks. What could have caused such curvature without breaking the rocks?
3. There is a second anticline visible just off the Veach Gap Trail a little further up the trail. Which anticline has the larger fold, the anticline at the posted coordinates or this second anticline?
4. Do you suppose there are other, similar anticlines in the area? If so, where are they?
5. Optionally, take a photo of yourself in front of one of the anticlines. Express amazement that such hard rock has been bent like modeling clay!
Additional Hints
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