The author stumbled upon this mysterious rock while out hunting for geodes. Photo by Keith Krizan

A funny thing happened on the way to Corral Nuevo, and that was a good thing.

One of the books that I have been using as a guide to finding interesting rocks has been “Gem Trails of Arizona” by James R. Mitchell. The book divides the state into four regions, with 25 collecting sites in each. Mitchell describes each site: how to get there, the difficulty of the drive, where to park and what you might find. In addition to useful advice – wear goggles, bring plenty of water, etc. There are also maps, almost like pirate treasure maps, with mileages between turn dots and X’s that mark the spot. 

Site #99 in the book is entitled Corral Nuevo Geodes. Mitchell describes it as “one of Arizona’s most plentiful supplies of crystal-filled geodes.” To get to Corral Nuevo one drives west from Exit 12 off of I-19 in Rio Rico onto SR 289. About 9.5 miles in, just before Peña Blanca Lake, FR 39 goes off to the southwest onto what is marked on some maps as East Ruby Road. This road is not too rugged, and it eventually takes you past the entrance to the ghost town of Ruby to the very much alive town of Arivaca. Pavement is lost just beyond the turnoff for the lake and not gained again until you are nearly into Arivaca, but the views of the Atascosa Mountains and Montana Peak are well worth the drive.

Eleven miles in on East Ruby Road, FR 4186 is a right turn that will take you to Corral Nuevo 2.3 miles further in. The more numbers that are used to designate a road, the less likely it is to be traversed by a passenger vehicle. 4186 is 2.3 miles of rough road. It goes through sketchy, wet washes and up deeply rutted trails.

When you reach Corral Nuevo, there exists a working corral. Park there and enter the wash just beyond. The rhyolite dikes that contain the geodes are a few tenths of a mile down the wash.

According to Webster’s the word rhyolite comes from the Greek word rhyax, meaning “a stream of lava” and the rock name suffix “lite.” It is an extrusive igneous rock that has a high silica content. When it cools quickly near the surface it can form small crystals of quartz and the specimens found here are considered by to be of gem quality.

One of the great pleasures of going to places you’ve never visited is the chance to stumble onto something unknown and unexpected. On our way to the “Outback” of these Sky Islands we have come upon many an interesting thing. An old cemetery in Harshaw, foundation ruins in Alto, abandoned stamp mill and smelter sites in the Dragoons, slag in a dry stream bed in the Patagonia Mountains.

On our way to collect in the wash that holds the Corral Nuevo quartz geodes we found a most unusual rock. Triangular in shape and standing over 20 feet high, this limestone beauty is loaded with randomly occurring holes on one of its vertical faces. Swiss cheese comes to mind. The holes are nearly perfectly round and range from 12” to over 24” in depth. The sides of the walls within the holes vary. Some are straight down. Others have concentric rings going from wide to narrow to wide and then again to narrow

Being familiar with the grinding stones, or “metates,” of Mesoamerican cultures, I at first thought that the now vertical surface with the holes had once been horizontal; perhaps it had been undercut and cleaved from the low canyon wall, falling into the wash and just happening to land as it did. But the depths and the shape of the holes would seem to have made it impractical for the grinding and recovering of the seeds and grains used for cooking. My second thought was these holes were naturally occurring, caused by the action of pebbles moved around by a current when the face was horizontal and before it was undercut, collapsed, and ended up vertical in the wash.

I’ve tried to crowdsource the answer to my little mystery by posting photos to that font of modern-day knowledge, the internet. I received in return suggestions ranging from the man-made (metates, drilling test holes or signpost type pointers) to the natural (from the action of stones caught in a current in a hole) to the otherworldly (aliens).

The site is within a wash where a nearby spring always seems to provide water to the surface. Even though I’ve not seen any glyphs in the area, I am wondering if the holes were made while the rock was already in the vertical for some sort of ceremonial purposes.

Can anybody please give me a definitive answer? Anybody, anybody?

Manmade? Natural? Aliens? Email your theory to