South Mountain in Phoenix, Arizona is an interesting place for a
naturalist to take a walk. The mountain itself is what's known amongst geologists as a
metamorphic core complex - an exposure of deep crust that has been
rapidly exposed during extension. And sitting on top of the exposed
layers of ductilely deformed lower crust, there is an arid environment that is home to some exciting cacti.
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| The view back down Telegraph Pass Trail |
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Telegraph Pass Trail winds up to the South Mountain ridge through an incredible variety of cacti. The Saguaro cactus is the most prominent, with its iconic arms and massive size. Their impressive stature is all the more impressive when you learn that a Saguaro doesn't grow its first branch until it reaches around 100 years old, and reaches full height of around 40 ft at 200 years.
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| California Barrel cactus (top left), Saguaro (top right), some small barrel cactus (bottom left) and cholla (bottom right, the fuzzy one) |
While walking along the trail, I was fascinated by the variety of needles on the different cacti species. The larger man-sized California Barrel cacti have long, purple needles that sit in spiralling rows. The
jumping cholla is
covered in tiny spikes that give it its fuzzy appearance and the nickname (teddy bear cholla). The cholla is especially adept at inflicting pain and annoyance thanks to its microscopic barbs that line its needles (
check out this awesome SEM image of the needles!). And I also came across a small little barrel cactus (that I haven't ID'd with any certainty) with black fishhook needles, ready to snag the unwary.
Also scattered amongst the cacti lie rocks covered with petroglyphs left behind by the Hohokam People, an early-agrarian culture that flourished in the American South-West between AD 1 to 1400. Many of the petroglyphs depict animals, but there are also many spirals and concentric circles, such as the one pictured below.
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| A Hohokam Petroglyph |
