Geo-pic of the week: Pinnacle Mountain

Pinnacle closeup edited (1)

This is a picture of Pinnacle Mountain – one of several steep-sided hills up to about 1000 feet tall, located at Pinnacle Mountain State Park, northwest of Little Rock, Arkansas.  Though its appearance may be misleading and its origin is debatable, Pinnacle Mountain is not a volcano!

What’s intriguing about Pinnacle and the smaller nearby hills is that they’re sandstone lenses surrounded by shale.  That, from a geologic perspective, is difficult to explain since sedimentary rocks are suppose to form in layers, not lenses or blocks.  This has led geologists to a variety of interpretations for their origin ranging from giant undersea landslides, to sand that got trapped in the empty gouges left by large undersea landslides, to beds of sandstone caught up and scrambled with shale beds along huge thrust faults.

Whatever their origin, because they are sedimentary rock and contrary to some satirical publications I’ve seen circulating online, they are not volcanoes and they are not going to blow up!

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