Fossils

Even when confronted with the rapid obsolescence of computers and cell phones and cameras, one can still lose sight of how much has changed in science since the men at Los Alamos set off their first test explosion.

Grade school is still the time we learn about the geologic past. Young boys are still infatuated with the Jurassic age of dinosaurs. For some reason, I got struck by the Pennsylvanian era of swamps and evergreens when coal was being formed.

Back in those days in the middle 1950's, the world began with the Precambrian. I never thought why, it was simply so. At that age, one didn’t consider the wonders of zero either or worry about negative numbers. One simply learned to count, one, two, three.

While I was reading Ted Galusha and John Blick’s article on Tertiary sediments in the Española basin, I suddenly realized why. When I was a child a principal way to date rocks was with fossils. There were no fossils before the Precambrian age. There was no life as we know it to produce fossils. The beginning of life was the beginning of rocks.

Oh, there was something called the Archaean to account for those things that were obviously below, but had no retrievable history. They simply existed after the big bang and solidification of the earth’s crust, but before time.

The problem with fossils is they often are dated by the strata in which they are found. In turn, they are used to date other strata in a closed, self-referencing system with few points of independent verification.

The whole time I was reading Galusha and Blick, all I really wanted to know was how old are the rocks Daniel Koning says lie under my house and how did they get there. Their answer was:

“The Tesuque Formation apparently was deposited through part of the Hemingfordian, Barstovian, and most, if not all, of Clarendonian (early Pliocene) time.”

To get anything more specific than late Miocene, I had to look up those fossil groups, which were filled with animals both strange (camels, rhinos, horses) and extinct (oreodonts), many of which migrated across the Bering land bridge.

At least, when you do go on-line for information, there are artists’ attempts to grapple with what those bones looked like when they were moving about. They don’t answer my questions about age, but they are diverting.

Dating techniques were beginning to change when I was a child. At Enrico Fermi’s University of Chicago, where so much preliminary research into the nature of matter and the predictable half lives of radioactive isotopes was done that lead to the bomb, Willard Libby was applying the same model to carbon to develop methods for using the carbon-14 isotope to date items that contained carbon.

By the time I was in college, his methods were being accepted, but they were only good for 62 million years. That’s the Tertiary Eocene. It could date a mastodon, but not a dinosaur. Still that was more than adequate for me. I was becoming an historian, not a zoologist or geologist.

Since I last paid attention, engineers have used all those technical skills that led to things like computers and satellites used by cell phones to develop other tools for probing the past. They send electromagnetic signals and interpret the resonances. They use the half-lives of other elements like potassium and argon. Their papers become tables of graphs and columns of numbers one has to take as true while looking for the scattered intelligible words in sentences like:

“Other east-west gravity profiles between latitudes 32^o and 38^o also show this asthenospheric diapir, which thus forms a ridge-like Moho unwarp approximately parallel to the surface trace of the rift.”

Thank God for Google and the ability to look up any word, to learn aesthenospheric refers to the mantle and Moho the boundary between the mantle and the crust, to learn something detectable exists deep in the earth below the rift valley that may account for all the geologic activity.

These tools which I have to take with the same faith I once took the word Precambrian are probing the time when the plates were colliding billions, not millions, of years ago. That really is astounding. The latest Geological Society of American time scale breaks the Archaean into four phases and has a created a new “dates unknown” period, the Hadean for older than 3.8 billion.

The River Runs

Wednesday it rained, day and night.

Thursday noon when I went to the post office the river was running higher and faster, the color of caffè latte.

I thought, ah yes, of course, the river’s running. It rained. I didn’t think, I’m seeing the great shaping force of this part of the country roused from a long seasonal slumber.

I didn’t connect even though I’d spent the morning looking at Daniel Koning’s “Preliminary Geologic Map of the Española 7.5-minute Quadrangle” which shows a lopped triangle with the Rio Grande and Route 285 on the sides, the Rio Pojoaque to the south and the Santa Cruz river on the north just above where I was driving over the Griego bridge.

He shows the road near my house skirts what he labels a “geological contact.” The soils to the river side have recent alluvial origins. The ones to the east date back to an earlier Tertiary period. Since the time before the great glaciers when the river began to connect the discrete basins of the rift valley, water has been digging and padding its channel.

It’s removed or redeposited the existing tertiary sediments, or perhaps both at the same or different times, and left a boundary area that needs no geologist to recognize.

I went back to today to the Griego Bridge to see the river at the point the Santa Cruz enters. The current was slower, but the water was still carrying dirt. Gravel and sand have been deposited where the dammed and controlled water flow of the one meets the less tamed Rio Grande.

Then I drove home and looked again at that “geological contact” out the car window. You could imagine the grass as some great sea lapping against dunes. And like ladies of a certain age who once were rivals and now nod when they meet, you can only guess their pasts from the differences in their outerwear, their vegetation.

White Sand

There are things you always say you’re going to do, and something always intervenes.

Every time I drive north towards Taos from Velarde I tell myself I really must pull over on the way back and look. Fallen lava boulders litter the right shoulder as you rise. By necessity, the turn offs are all on the other side. The road has too many blind spots to simply cross over.

But then, when you’re coming home, you’re, well, coming home. It’s a different mental state. There’s never time to pull over.

Well, I finally did it. When I was coming back from the Dixon area a few weeks ago, I pulled over in some of the places between Embudo and Velarde where the rift is narrow, the Rio Grande close to the road.

The look up towards Taos isn’t quite as dramatic as it was when I was driving north - but then it’s like the drive down La Bajada Hill - there are no turn offs when the rocks are the most menacing. The turn offs are only where there’s room, which, by definition, is not where it’s most exciting. Perspective is different from fifty feet across the road.

The river turns out to look like a river there, like any river anywhere in the country where water actually flows and doesn’t simply ripple around sand islands as it does in Española. Nice, unusual actually for New Mexico, but conventional still the same.

Then there’s the unexpected, the thing you didn’t know was there because you never stopped.

In this case, there was a patch of white sand near the river with Russian thistles and purple asters. You think, wait a minute, white sand? New Mexico?

The White Sands in the Tularosa Valley are gypsum dunes. This glittered in the sun. It had to be ground quartz, which of course is as much silica as sand. In fact ground pure quartz provided the material for Venetian glass makers.

Quartz has the greatest weather resistence of any of the rocks in the area. It’s often the last remaining eroded rock from the Sangre de Cristo. This “dune” looks suspiciously like how that sedimentary grey rock I saw earlier in the day beyond Dixon would look if everything soft disappeared and left only the quartz and shining mica. And it photographs the same way, too brown and out of focus, or all glare.

Geology for Dummies*

* Well, not exactly dummies - but for those of us born into an earlier era, there comes a time when it’s necessary to step back and try to grasp what any modern child might learn today in grade school.

When I was young in glacier dominated Michigan there were simply seven continents, and some rather mysterious drawings of folds, faults and subduction zones. Since nothing really mattered before the Pleistocene, I ignored those drawings.

Since then, scientists have agreed on the existence of plate tectonics and continents are no longer givens, but the results of processes. Here in the Española Valley we’re on the boundaries of plate activity that I’ve spent the past few hours trying, once again, to understand.

The Wikipedia entry on the Wyoming Craton has a useful schematic showing the elements that coalesced or were absorbed into the Laurentian plate that became North America. This part of New Mexico was somewhere on the boundary of the collision of a southeast facing section of that continent with Yavapai-Mazatzal that resulted in lines of weakness that were subsequently buried under layers of sedimentary shale, sandstone and limestone.

Laurentia later overrode the Farallon plate in the Pacific. As the last, western most section of Farallon was swallowed, undissolved bits on the eastern side tipped up as part of the mountain building that produced the Sangre de Cristo.

When the Farallon plate finally did disappear, one section of the North American plate began rotating clockwise to drift into the newly vacated area. As it shifted, the great rift began to open as one part of the land shifted with it and another stayed in place. As the rift expanded, blocks of land roughly defined by those old Yavapai-Mazatzal collision lines dropped, some facing east, some facing west and magma welled through the Jemez Lineament.

The Emdudo faults are the southwest-northeast northern frontier of the Española valley and the La Bajada faults part of the southwest-northeast running southern one. Almost no displacements occur without some tilting. Those visible at the Cochiti exit are mild, those a few miles away at the Garden of the Gods are extreme.

The layers everywhere are probably the same, but what’s visible is probably as much a function of road building as natural forces. At La Bajada the lower red stones are more visible than the lighter colored stones above that either are covered or have washed away. At the Garden of the Gods, the limestone has lasted longer than the softer red sediments.

Above picture from Garden of the Gods on State Road 14; the others from La Bajada at the Cochiti exit.

Between Dixon and Picuris

Now that I have a new camera I have to test it.

My usual method for day tripping has been to look at the map, find something that looks interesting, load the ice chest, and start driving.

There is nothing that can repeat the absolute surprise you feel when you come upon something like the Abiquiu Dam when you’re not expecting it and nothing you want to do to deaden that heart-stopping awe, that sense of unity with all the explorers from the stone age to the present who’ve been there before.

When I get home, I start to read about the place I’ve just been. Then when I go back, I have some better ideas what to look for and some idea about where it’s safe to pull off the road.

Saturday, I took the new camera back to that road beyond Dixon where I had problems with my tires earlier this summer.

After NM 75 leaves Dixon, it feels very much like a typical mountain road with the Rio Embudo on the right side, an occasional gorge coming down from the left, and continually opening V’s as the road climbs towards the Sangre de Cristo south of the Picuris mountains. The trees are all still juniper, but closer together than they were below.

Then I came to a section where raw rock was exposed, standing on edge. It looked like shale at the Rio Grande end, then layers of sandstone. However, they seemed so weathered they had no distinct colors, and I’m not sure I even know what shale looks like, other than it’s gray.

My first thought was, why on earth did anyone go to the expense of blasting a road through here. This is New Mexico, where they didn’t widen the road to Los Alamos until after I moved here. Route 75 was described as “a graded dirt road” in the 1930's WPA Guide when the road that came up from Chimayó through Truches and Las Trampas could get you to Picurus pueblo and Peñasco.

I spent yesterday learning absolutely nothing.

The Española Basin, which tilts west down to the Rio Grande, ends at Velarde. The San Luis Basin, which tilts east, begins farther north. Between the two lies a diagonal belt of disruption that goes from the Picuris mountains to the northeast through the Embudo Fault across the peninsula between the Chama and Rio Grande rivers toward the opening into Santa Clara Canyon.

I presume I was somewhere on the edge of that fault, but can get no confirmation. Is this what a fault looks like?