Land Beneath My Feet

Hiking the Quebradas Back Country east of Socorro, NM on 14 December 2019

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Land beneath my feet demands attention. Step upwards watching for the prickly cacti populating this arid country. Step downwards, gingerly, not putting too much weight on that potential stepping stone. Probe it first with your hiking pole. It crumbles at the slightest poke. Gypsum, I finally concluded. It's the stuff of dry wall, and it's all over this place. Cloaked by dark, mossy overgrowth, it is white and crusty, like a snow that's neither cold nor wet. Chunks of it crumble with little effort between my fingers. Pretty sure now of its identity -- plain old calcium sulfate -- I taste it. Not salty, not a trace of halite detected. How strange, I think, to find it here.

One of the advantages to being a beginner, as I am in geology, is the ease at which one is amazed. In my mind, "gypsum" immediately conjures images of White Sands National Monument. It is found in the Tularosa Basin 120 miles to the southeast. Its white sands are not the usual quartz sand but rather finely-powdered gypsum, blown by a steady westerly wind, from playa into the Monument's vast field of ever-shifting dunes.

Playa are flat lake beds thirsty dry much of the year. Lacking a natural outlet, playa water escapes by evaporation, abandoning its load of dissolved mineral solute as a crust of opaque, white gypsum and translucent crystals of selenite. Elsewhere in the American Southwest, other evaporite minerals, such as borax and trona, are found on vast, flat, desiccated lake beds. Searles Lake in California comes to mind. I remember my time there, the afternoon April sun becoming blinding in its reflecting off the crunchy white surface under foot.

Once this New Mexican land too must have been flat. Once. Long ago. Long, long enough ago for time's slow subsequent actions to accumulate, eventually altering the land and forming the rugged terrain over which I climb over now. By folding and faulting, lifting up and eroding down, moving by wind blowing, depositing by water flowing, and wasting by gravity falling, the landscape inevitably changes. "Once" might be 160 million years ago, in the middle Jurassic Period, that is, during the heydey of the dinosaurs, for, as geologists say, New Mexico was then submerged beneath a huge Lake Todilto [1]. Something -- but what? -- must changed the climate, making it drier and hotter, leaving Lake Todilto to shrink, shrivel, and disappear. Perhaps the gypsum here precipitated then.

By four miles in, of seven miles total, and my knees are feeling it, all of the stepping and zigzagging up, down, and around. We are hiking in the Quebradas back country roughly seven miles due east of Socorro, New Mexico. "Quebradas" is apt, for the word denotes a ravine, especially one formed by an arroyo. I wash down a couple of ibuprofen tablets with what water I have left. Of the dozen of us on this hike, I am one of the quiet ones. I want to read the landscape and understand its deep time history. Anyway, lacking both grandchildren soon to be born or even adult children recently married, I have little to contribute to conversations heard around me. My family history goes longer. My children are all adopted. They are elements of the Periodic Table born in the exploding death throes of ancient stars predating the birth, by hydrogen fusion ignition, of our own sun 4.6 billion years ago. From all of that sound and fury comes the calcium, the sulfur, and the oxygen composing this soft gypsum and the land beneath my feet.

Footnotes
1. Ancient Lake Todilto may have only covered what today is southern Colorado and northern New Mexico. If so, it would not explain gypsum deposition near Socorro. An alternative source of evaporative gypsum deposition is the disappearance of a vast sea covering southern New Mexico in the Permian Period, 286 to 245 million years ago. See Halka Chronic, Roadside Geology of New Mexico, 1987, pp. xiii, 28, 201,

posted: 2019-12-16, last edited: 2019-12-16