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.