Geodes in Arizona?

I am not a big rock hound. Perhaps it is because I look at my rock collection and remember how I strained my back lugging those rocks out of a canyon, only to toss them in my flower bed to be re-discovered the next time I pull weeds. Nonetheless, people sometimes ask if I know where to find various rocks, minerals, or fossils. Usually I do not know, but recently a friend asked me where to find geodes in Arizona – and I happened to know a place.

The place I am familiar with is in the shadow of the Mogollon rim north of Payson, Arizona. They aren’t the prettiest geodes, but they are plentiful and easy to find. To get there, turn east on the Houston Mesa road from Arizona 87 (about a mile north of the junction of 87 and 260). Follow the Houston Mesa road until it ends at a dirt road called “Fire Control Road”. Take a right on Fire Control Road (East), cross the East Verde River, and drive about one mile. On the north (left) side of the road, there will be a small hill. There is a wide spot in the road suitable for parking. Cross the small drainage ditch on the north side of the road, and head up the hill.

Keep your eyes to the ground, because the hillside is covered with geodes. They look like tan globs between the size of a walnut and a potato. Carry a hammer with you so that you can bust a few open and learn what the geodes look like.

Paleozoic strata is not my expertise, but I believe these geodes are being weathered out of the Devonian-age Martin Formation. The geodes themselves are not Devonian age; they formed through diagenesis after the Martin Formation was deposited.

While a hammer is a quick method of viewing the inside, they look much better if cut in half by a diamond blade tile saw. Much of the inside cavity is filled with calcite, and that can be dissolved away by immersing the geode halves in a weak hydrochloric acid (pool acid) solution over night.

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