Tag Archives: Pinnacle Mountain State Park

New Publication: Geologic Road Guide to Highway 10

 

01-Overview

The Geologic Road Guide to Arkansas State Highway 10, a Geotour of the Southern Arkoma Basin Fold Belt and Related Ouachita Mountain Tectonic Zones by Drs. Richard Cohoon (Emeritus), Jason Patton (Associate), and Victor Vere (Emeritus), Professors of Geology at Arkansas Tech University, is now available for download on the Arkansas Geological Survey’s website.  Here’s the link:

http://www.geology.ar.gov/roadside_geology_series/rgs02.htm

The route begins at Petit Roche Plaza in the River Market District of downtown Little Rock. “Petit Roche” was the name given to the first rock outcrop early explorers encountered on their way up the Arkansas River.  It is near this outcrop that the eastern end of Arkansas State Highway 10 (AR-10) is now located.  From here, you will tour the 139-mile length of AR-10 to its western terminus at the Oklahoma state line, just past Hackett.  This route traverses a beautiful and geologically diverse cross section through the mountains of western Arkansas.  The stretch from Ola to Hackett is designated as an Arkansas Scenic Byway.

An overview of the physiography of Arkansas, the concept of geologic time, and the rock formations and structural regions encountered along AR-10 introduce the reader to the detailed Road Guides that follow.  The Road Guides describe the rock outcrops and geologic features along particular sections of the route.  They contain many wonderful color photographs and color-coded geologic maps to help travelers understand the landscape passing outside their windows.  Travelers are encouraged to get out of their vehicle at several places to have a look at the rocks, perhaps gaining a new appreciation of their significance.  An illustrated glossary defines words and concepts that may be unfamiliar to those without an earth science background.  Appendices direct the traveler to several interesting side trips just off the main route and detail the characteristics of the gas and coal resources in the Arkoma Basin.

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This Geotour is written to be of interest to the general public, to students of geology, and to professional geologists who want to gain a more in-depth understanding of this beautiful and geologically complex region.  So the next time you’re thinking of taking a scenic drive through the mountains of western Arkansas, consider traveling AR-10.  And don’t forget to take along the Geologic Road Guide to make your drive more enjoyable and informative.

Richard Hutto

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!