Potts Canyon Geodes

I was in Tuscon checking out all the rock shows when I spotted a super hollow geode thunderegg with pearly blue chalcedony lining the interior. I had not seen an egg quite like it before so I had to ask. The nice lady at the booth told me it was from an area east of Phoenix in the foothills of the Superstition mountains. She said that the geode glowed an emerald green under ultraviolet light and told me to take it over to the ultraviolet booth and check it out. This egg lit up as soon as I closed the curtain, and I was smitten... I must find where these eggs came from.

I checked my rock library and found the area mentioned as the Potts canyon geode site in "Minerals of Arizona" by Neil Bearce. This site was listed as very difficult to get there, to walk around, and to extract the material. Sounded like my kind of place, maybe there was still something to find. I left Tuscon right after the 'big show' and headed north to the Superstitions.

If the desert is your thing, this is the place. The Sonoran desert is most beautiful here. Tree-like cholla and saquaro everywhere, it is just gorgeous. The Boyce Thompson Arboretum is just five miles from the entrance to this site and is a must see. They have cactus from all over the world and a nice South American desert area that looks like the Patagonia of Argentina.

This area is also where Phoenix residents go to play. The big thing is to take your 4 wheeler on a 30 mile loop up into the superstitions and back down. This loop has many turnouts to set up a camp, and I found a nice place just off the road. I unloaded the 4 wheeler and joined the masses using this road until I came to the turnoff to Potts canyon. The Potts canyon road is not.. well, its not really a road. Don't take your nice truck here, this is for 4 wheelers only. If you do, and you get stuck, don't worry... lots of folks use this area, someone will be by to help out. There were several trails going up and over the mountains that were to die for. Sheer drop-offs on either side, superb views, just a 4 wheelers dream.

Finding the area mentioned in the rockhounding book was easy. There was an old perlite quarry next to a prominent volcanic knob. The idea was to check out the rocks and boulders around this knob for vugs and geodes containing the blue chalcedony. I did a lot of checking out but no collectable chalcedony showed up. There were a few vugs showing blue in the big gray boulders, but no geodes. This is so typical of the sites in the rockhounding books. There is just nothing to be found. These sites have already been hunted by thousands of folks just as ambitious as I... so I have no chance. I took my wife with me several times chasing the specimens pictured in these books and she now refuses to go with me anymore. She wants me to write about the goose-chases these books send you on. I must say though, as depressed as I was at that moment for not finding that Potts canyon geode, I was in a most wonderful place. I would not be here if not for that rockhounding book. So.. I had to chill, and just enjoy where I was. There was a little creek with water just down from the volcanic knob so I headed down to soak my feet. As I was checking out all the critter tracks in the sand of the creek bed, I looked up on the hillside of the opposite bank and there was a big blue spot halfway up the mountain. It looked like blue chalcedony, and there was another and another in a diagonal line stretching for 100 yards up that hillside. This turned out to be a vein of giant half thundereggs so entrenched in their host, the tops were all chiseled off but the bottoms were left behind. I spent half a day with hammer and chisel to get up one of these bottoms. This specimen was really big with lots of eye-catching blue chalcedony. I could only imagine how this half geode would look under a black light. I had my specimen!

For the next few days I hung around in this area and checked out the Barking Spider mine for wulfenite, and the Hewitt canyon marble. I swung back to Potts canyon for a day on the 4 wheeler trails and decided to hike around one more time. I hiked down to the creek and stayed in its bed for a few hundred yards downstream. There, in the stream bed, was a big boulder covered in small blank (containing only matrix and no agate) thundereggs. These 'blanks' are common in some thunderegg beds. They are the result of eggs having no hollow center, created by gas, early in their development. If there was no hollow, there was no agate. This resulted in blanks having only worthless matrix in their centers. The Baker mine in New Mexico is notorious for its blank thundereggs. It takes real skill to know if an egg has agate or is a worthless blank. At Potts canyon, the blanks are numerous. The hillside where I dug out that bottom geode half, was graced with lots of big blank thundereggs. The only way to know if what you dug was a good egg, was to stay in that particular vein where the eggs contained agate. The other veins around it were all full of blanks. You can chip off a small "window" on one end of the nodule to see if there is agate, but you risk ruining the geode.

So... after busting a few of the small blanks on this boulder, I noticed a small crack going across one end. I got out my chisel and went to work. This large boulder turned out to be one huge 130 pound thunderegg! Looking up the hill from the creek I spotted two more geodes sticking out from the same vein this huge boulder egg had weathered from. I knew these eggs would contain agate, so I went to work trying to get the eggs out gently without breaking them. The vein that the thundereggs was in, was like hard concrete. I chiseled for hours until I could no longer feel my arms. My hands were a bloody mess and I had only one geode showing any hope of coming loose. As I was swinging the hammer with tired abandon, I missed the head of the chisel and hit the geode instead. The top of the geode popped off and displayed to me the most awesome site. A beautiful blue chalcedony lined geode with opal? or waterline agate pooled in the bottom. Although I did not destroy the geode, I decided to rest up for a day before attempting the extraction of the other geode, just barely peeking out of the cemented vein.

The next day was spent with hammer and chisel and one really stubborn blue chalcedony thunderegg. I knew it was going to be a great geode to cut if I could only get it out whole. With its twin, top off, resting at my camp, I stayed at a gentle pace, kept my focus, and extracted the geode without any disasters.

This hunt, while seemingly hopeless at first, turned out to be quite enjoyable. A lesson learned about chasing the sites described in the rockhounding books. Don't give up on the area without giving it a good hiking over. The good stuff is just beyond that big hill. Of course this is also a good way to get lost... experience talking.

The Geode Hunter

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The Potts canyon area. The volcanic knob and large boulders that were supposed to contain the chalcedony. This hillside has been wiped clean by previous rockhounds. I spent half a day busting up some of these boulders and got nothing.

The Potts canyon area. The volcanic knob is to the right of the photograph and the perlite mine is in the foreground. The vein of thundereggs I found was in the v-shaped strata of the hill across the small creek in the center of this picture. There is a road traversing the top of this hill that is really fun. It ends at a mining claim just on the other side. Chalcedony is prevalent in the boulders and rocks on this claim but it wasn't worth looking to see if it was still valid. All the thundereggs showing on this claim were blanks.

A vein of blanks. Just below the blanks is a vein of good stuff as evidenced by the agate showing in the small vug at the bottom of the picture. The veins with the blanks were easy to avoid as all the tops were beaten off of them by previous rockhounds.

The good stuff. The broken geode has been ruined, but the one under it can still be dug up whole and saved for the saw. Usually I would be sickened by the destroyed geodes, but they led me to the good stuff and I didn't have to do any testing (busting) of my own. There are so many blanks here.

Blue chalcedony thunderegg. This geode broke during the extraction. Really cool stuff. The "bubbles" seem to have transferred into the cavity.

Closeup of the blue chalcedony. It has a pearly luster that reminds me of the smithsonite found in the old Kelly mine in New Mexico.

A thunderegg top showing the white waterline agate or common opal that pooled at the bottoms of some of these geodes.

The big boulder that was. Notice the one inch pool of opal(?) or agate at the bottom of the cavity.

A great evening at Potts canyon!