Conor Watkins' Ozark Mountain Experience

Field Trip Guide to the
Geology, Scenery, And History of The Salem Plateau of the Ozarks
–In The Buckhorn, Dixon, and Rolla Areas
For The Fall 2003 MVOR hosted by MSM Spelunkers at Shriners Club, Buckhorn, MO - Oct 3-5, 2003
By Conor Watkins, University of Missouri - Rolla

Stop 4: Conical And Slaughter Sinkholes

The bedrock in the Salam Plateau of the Ozarks consists mainly of dolomite, which is made up of calcium magnesium carbonate (CaMg(CO3)2).  Natural and man-made acids in the water dissolve many carbonates, which lead to karst processes and features.  Carbonic acid is the largest player in the dissolution of bedrock.  This weak acid is formed when raindrops combine with carbon dioxide in the atmosphere and in the soil as organic material decomposes.  As this acidic water seeps into the ground, it slowly dissolves the rock.

This process leads to the creation of sinkholes, caves, springs, losing streams, and other karst features.  Missouri has some excellent examples of karst.  As for sinkholes, the area has both recent and ancient examples.  Some of the best and easiest to see examples of geologically recent sinkholes are Conical and Slaughter Sink.  These are along a county road and on National Forest land so angry landowners with shotguns are not a worry.  After viewing these sinks, one might want to visit Onyx Mountain Caverns (http://www.missouricaves.com/onyxmtn.htm), a commercial cave very close to the sinks.  It was created by the same karst processes that made the sinks.  This is Conical Sink, the smaller of the two sinks.  Its close proximity to the road has made it an illegal dumping ground for years so expect to see tires, refrigerators, and other discards.  Dumping in a sinkhole is a particularly bad idea since these features serve as natural drains for rainwater. That garbage you see ends up in the groundwater and eventually drinking water.  That old washing machine is mainly an eyesore but used motor oil and car batteries are toxic.

Next, turn exactly 180 degrees and start following the small trail into the woods.  Keep following until the large overlook is reached.  This is Slaughter Sink, one of the largest sinkholes in the state.  It is hard to imagine that this feature was formed when the roof of a cavern collapsed thousands of years ago.  The bottom of this sink can be reached by following the trail down through a small natural bridge.  A more gradual hike is available if you walk farther down the road.  Excellent exposures of Roubidoux Sandstone are visible at the bottom.  Satellite and King Sink are a similar example of two sinkholes in the area.  These two sinks are not as impressive, harder to get to and find, and are partly on private property.

The view looking down into Slaughter Sink reveals the scale of this feature.


The deep sinkhole is steep sided around most of its rim although there is a
more gradual way down farther to the north.

DIRECTIONS - To Conical and Slaughter Sinks:

To get to these two sinks from Devil's Elbow, take Hwy J from Z north across I-44 to the outer road.  Turn right at this junction and follow the signs as though you are going towards Onyx Mountain Caverns.  After turning left onto the first gravel road, look for a barbed wire fence and often a “No Dumping” sign on the left side of the road with a drop-off on the other side (Conical Sink).  Park here and explore.

Conical Sink is visible from the road and is a popular illegal dumping ground.
Notice the white appliances in the bottom.

(C) 2004 by Conor Watkins