Geological Musings

During the first half of my life, encompassing three decades, I lived in the Midwest. I didn’t know any better, I guess. I had traveled through the west at times, and I was impressed by the landscapes, but once my ex-wife and I had kids we were more or less stuck there for quite a few years.

Almost a year ago fate stepped in and changed my life. I met a woman from Nova Scotia and she convinced me to leave my old life behind and come to Southeast Arizona, and here I am.

My attitude towards geology in the Midwest was casual and intermittent. The areas I lived in were blanketed by glacial till and the pre-cambrian rocks were buried, just a subject of imagination. Limestone cliffs could be seen along the major rivers, such as the South Fabius, but the region had been quite static for many thousands of years, ever since the last Wisconsan glaciation ten or twelve thousand years ago.

The Southwest desert regions opened my eyes. Such geological tumult! Uplifts and volcanoes were followed by millions of years of placid oceans; fragments of limey shells shed by dying phytoplankton and zooplankton drifted down from ancient seas. Those fragments formed layers of sediment which became limestone reefs, and these reefs were uplifted by violent mountain-building events caused by tectonic movements of the continental plates millions of years ago. This was followed by eons of years of erosion. The valleys in this area became filled with thousands of feet of alluvium, sandy and gravelly soil which doesn’t retain the scanty rain which falls; it all filters down into a water-table which is being sucked up by people, those who have settled in the valley and can afford wells.

If you look at the satellite views of the valley using Google Maps you can see the agriculture in the valley. Circles of green show the tracts being irrigated with circle-pivot irrigation, much of that hay land. I was surprised to see,when I first drove through the valley, how many new pecan orchards there are. Young groves of pecans growing on irrigated land. At the local Safeway grocery store in San Jose I also noticed that pecans these days cost about twelve dollars per pound.

Sitting on my back porch I can see the southeast wall of Tombstone Canyon. A band of limestone is very evident near the top; here’s a photo:

This layer of limestone was violently heaved up during a mountain-building episode millions of years ago, and there it remains, showing evidence of fossil organisms which lived in a long-dead sea.

You can’t escape geology in the Southwest. It’s in your face if you have a contemplative and observant nature.




Filed under Arizona, Essays and Articles

6 responses to “Geological Musings

  1. Joan

    Eloquent, Larry. Beautiful terraine but I feel a need to defend Missouri’s part of the Midwest.
    While, our geological fun is mostly cloaked in eons of dirt and vegetation and not all bare naked as in Arizona, I do want to mention that you can get the same view of limestone layers while cruising down the Mississippi. Then there are our Ozarks. The fossil pickin’s are pretty easy in degraded limestone, and if you are ignited by igneous rocks, don’t just take Elephant Rocks for granite, Rhyolite formations? Hughes Mountain’s Devil Rocks. And for a natural water slide there is Johnson Shut’ins. Plus with all these you get some mountain greenery to go with. Sooo I’m just sayin’.

  2. I wasn’t really meaning to diss the placid geology of the Midwest. I’ve visited Elephant Rocks and Johnson’s Shut-ins and got a kick out of seeing basement igneous rocks revealed.

    Sure, you can see Mississippean and Pennsylvanian limestone bluffs along the Midwest rivers, but seeing those strata heaved up into the sky by mountain-building episodes is pretty cool!

  3. Joan

    Especially cool if the view is from your back porch! (grin)

  4. Darrell

    Larry, is the old silver mining activity now gone from Tombstone?

  5. Hi, Darrell. Tombstone, about thirty miles north of Bisbee, likes to call itself “The Town That Wouldn’t Die”. I don’t think any mining is going on up there — it’s mainly a tourist town, and a small one at that. Interesting that mining was being done there years before the Bisbee copper ore was discovered.

    Tombstone is out in the vast Sulphur Springs Valley, which once was a lake, while Bisbee is at the edge of the valley, in the midst of the Mule Mountains.

  6. Darrell

    Larry . . . . I’ve always been fascinated with Tombstone, starting with the 50’s TV series “Tombstone Territory”, also another ’50’s series “The Sheriff of Cochise”.. In Tombstone Territory, the lead-in called it “the town too tough to die”.
    I think the Tombstone silver lode was discovered by a guy named Schfflein (sp) in the mid 1870’s.

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