Geology is Everywhere! Visit Rocktown in the Crockford-Pigeon Mountain WMA , explore Joint Controlled Block Sandstone features and discover an EarthCache.
Overview
This is an EarthCache and has no physical container. The goal is to learn how natural cracks in sandstone (called joints) can divide the rock into large blocks—and how weathering then widens those cracks into the straight corridors and boulder “streets” you can explore at Rocktown. After reading the information below, visit the site, make a few simple observations and measurements, and answer the logging questions. If you have any questions, please reach out to me.
Rocktown is located within the Crockford-Pigeon Mountain Wildlife Management Area (WMA), and a valid Georgia Outdoor Recreation Pass (GORP) or hunting/fishing license is typically required for legal entry on this property. If you are just visiting for geocaching (and don’t already have a valid GORP, hunting, or fishing license), purchase of a single-day Georgia fishing license may be the least costly way to go (currently $5.00 for Georgia residents and $10.00 for non-residents). Visit their web site or download their app and get the necessary license prior to driving up here (little or no cell service is available up on the mountain).
Make sure you use the parking coordinates for driving here and then be prepared for a 1-mile (fairly flat) hike to Rocktown and back. It’s easy to get turned around while visiting, so making sure you have clear coordinates will help you avoid problems.
IMPORTANT: Obey all WMA rules and posted closures. This WMA property has seasonal closures/restrictions during hunting season, including being closed prior to 10 am during turkey season. Verify the access status of this property on your planned visit date. georgiawildlife.com or call (706) 295-6041.
Make sure you either print off the cache description or download offline data so that you have what you need when you arrive at GZ.
A Tape Measure or else something with a known length will be needed.
Logging Requirements
- Find a clear joint intersection (two prominent cracks meeting). Describe the angle between the joint sets (for example: near 90°, about 60°, etc.).
- Measure one block: choose a block bordered by joints on at least two sides. Estimate (or measure with a tape) the block’s length and width on the top surface (in cm or inches). Report your values.
- Joint spacing: along one joint set direction, pace or measure the distance between two neighboring, roughly parallel joints (fracture-to-fracture). Report the spacing and note whether it seems uniform or variable.
- Interpretation: Based on what you observed, explain (in your own words) how jointing plus weathering produces (a) the straight-sided corridors/passageways and (b) the blocky boulders.
- Photo: Post a photo of yourself or a personal item with the rock formation clearly in the background.
Location
Rocktown lies within the Crockford-Pigeon Mountain Wildlife Management Area (WMA) in Walker County. Rocktown’s diverse geological features exist because durable, jointed sandstone has been exposed for millions of years to groundwater movement, chemical reactions, and erosion, allowing multiple weathering processes to operate and overlap on the same rock surfaces. The unique rock formations here also make it popular with Rock Climbers, so don’t be surprised to see people climbing around you.
What is Joint Controlled Block Sandstone?
Joint-controlled block sandstone is sandstone that has been naturally “pre-cut” by a network of cracks called joints. Because joints often form in more than one direction, they divide the rock into large, block-shaped pieces. As water, roots, and freeze–thaw widen the cracks over time, the blocks become separated into boulders and the joints open into the straight-sided corridors you can walk through at Rocktown.
In geology, a joint is a natural crack in rock with little to no sideways movement—so it is different from a fault. Joints often occur as organized groups called joint sets, where many cracks share a similar direction. Where two (or more) joint sets intersect at Rocktown, they outline the edges of blocks and help explain why many passageways and boulder faces look unusually straight.
Where two main joint sets intersect at a high angle, the sandstone breaks into roughly rectangular or polygonal blocks. Water enters these fractures and weathering works fastest along the crack walls: freeze–thaw, root growth, and chemical alteration gradually widen the openings. As the fractures enlarge, individual blocks become separated and stand out as boulders and walls, while the joint traces become the straight-sided corridors between them.
How Joint Controlled Block Sandstone Forms
Joint-controlled block sandstone starts with solid sandstone that develops natural crack patterns (joints) as the rock is uplifted and the pressure on it changes. These joints commonly form in two main directions, so the bedrock becomes divided into large, block-shaped pieces.
Once the joints exist, water does the rest. Rain and groundwater seep into the cracks; freeze–thaw, root growth, and chemical weathering gradually widen them. Over long periods, the openings become the straight “streets” you can walk through, and the sandstone blocks become isolated as boulders and walls.
Side note: How does this differ from pedestal (mushroom) rocks?
As a quick comparison, pedestal (mushroom) rocks form when one boulder is undercut more at the base than the top, leaving a narrow “stem” under a wider cap. Rocktown’s blocky maze forms differently: intersecting joint cracks break the sandstone into separate blocks first, and weathering later widens those cracks into corridors.
SOURCES:
Roadside Geology of Georgia (pages 155-156) by Pamela Gore and William Witherspoon (2013) by Mountain Press Publishing
Crockford-Pigeon Mountain WMA | Department Of Natural Resources Division
Rocktown – Wikipedia
PSGT4. Joints and Veins – umich.edu
I used AI to help me write part of this description of this cache. I also used it to generate the image. The information was then cross-referenced to other sources.
