On Learning

My plunge into reading New Mexico geology has taken me back to my first weeks as an undergraduate at Michigan State when I realized there were a great many people in my classes who had attended much better public schools than I.

I recognized I either had to work harder to stay even or fall below my personal standard, which wasn’t particularly high, given that mediocre school system, but still high enough to refuse to accept failure.

I remember making the decision some Saturday when my room mates went off to the football game and I stayed behind to study. That day alone, when I first forsook the life of parties, I began developing an ability to teach myself.

It’s a helpful skill now when I read books or articles that claim to be aimed at both the beginning graduate student and the professional. They assume a level of knowledge, mainly about plate tectonics, but also volcanism, that I simply don’t have. It means constant on-line connections to find the definitions of words and concepts.

Fortunately, no one I’ve read so far expects a greater knowledge of chemistry or physics than I have. My high school science teachers were among my worst. Unlike botany, which has been so revolutionized by biochemistry that after some five years of reading about plants I still have difficulty with articles about photosynthesis that assume an understanding of concepts like feedback mechanisms and communication pathways, most of the geology I’ve read so far expects no more than a recognition of the symbols for elements, a minimal understanding of how compounds change, and the understanding of the technical definitions of words like reduction that have broader, general meanings.

This is probably because many senior geologists, those of my general generation, don’t know much more than they learned in high school. Once they specialized, they didn’t need to know more.

This shows most in their attempts to continue to use the basic concepts of Newtonian mechanics relating to the behavior of heat to explain the, to them, new phenomenon of plate tectonics. I don’t know if this was a valid assumption or not, but it was an understandable one given the conservative nature of both science and the human mind.

This brings me to the second thing I realized my first term in school, that I was more interested in interdisciplinary studies than specialized ones. MSU then had a required freshman course called American Thought and Language, which sought to meet the history, English and composition requirements in a single class that placed important writers in their cultural context.

I think I may have spent that long ago Saturday reading Roy Horton and Herbert Edwards’ Backgrounds of American Literary Thought, the first unassigned book I ever bought, trying to understand what my professor was saying about Puritanism. By chance it was the one he was using to prepare his lectures.

I found I wasn’t interested in knowing more and more about Emerson or the XYZ Affair, which is where a major in English or history inevitably leads. I wanted to know about the houses where readers of Emerson lived and the influence of the French more than I did transcendentalism or diplomatic history.

Such a pursuit, if it’s to be more than gadfly dilettantism, requires some discipline, as my graduate school professors never tired of telling us. More important it demanded that ability to plunge into reading something beyond one’s existing level of knowledge.

This brings me to the third thing I realized that first term in college, that no matter how much one learns, there’s always something beyond that’s unknown. Some are so taunted by that edge it drives them to push the frontiers of knowledge. It sends others with a strong desire for explanations into deep theological inquiries.

I realized one is either driven or tormented or one sets limits. I learned to recognize the point where the answers to my questions were pulling me into areas I wasn’t interested in pursuing, and simply accepted that such was the case and I could exist without knowing.

Deciding what to pursue and what to ignore is something we all do to get through the day. Someone once asked Penelope Lively, a novelist who delineated the undercurrents in human relations, how, once she was aware of such things, she could ever get through the mechanics of a family meal when a person simply must ask another to pass the butter.

Geologists must make those decisions when they write an article. They define the purpose, then exclude things that are extraneous. When Steven Whitman and Karl Karlstrom wrote about the formation of the North American continent, they realized their contribution was a series of drawings showing the progression through time. Indeed, one can learn a great deal by only looking at the pictures.

Their supporting evidence was drawn from the rocks themselves. They assumed you knew the rocks. I’m less interested in specific rocks than geologists or rock hounds, and so took their facts as facts not to be bothered with yet. I wanted to know why, not how to properly identify or date a specimen.

They took the Precambrian world as a given. They assumed you knew what that was or that it didn’t matter to understanding the phenomenon they were describing. As an historian, I was lost. If this part of New Mexico began as an island arc, I needed to know more about the ocean at that time, something they barely mention.

I went on line and innocently keyed in the search words Precambrian and ocean. I discovered some German heavy metal group called The Ocean had recorded an album called Precambrian. Interesting, but not what I wanted to know.

With some refinements in my Google search, I eventually found a chapter by Steve Kershaw on Precambrian oceans in his book, Oceanography. He was interested in why the earth didn’t freeze in its early years when the young sun wasn’t as hot as it would become, and so devoted a great deal of space to the Young Sun Paradox.

That’s indeed an interesting question, but not what I immediately needed to know. However, to cover his material for that hypothetical new graduate student, he did mention things I did want to know: when the oceans came into being, how deep they were, how much space they covered.

In the process he also suggested something I hadn’t thought about, how changes in the chemistry of sea water, as recorded by rocks, affected the development of islands like those that would become New Mexico.

The final thing I learned, not my freshman year, but when I actually became that hypothetical graduate student in American studies, is that no one ever tells you exactly what you want to know.

Whitmeyer, Karlstrom and Kershaw have all told me things I need to know, but they are writing for a general audience. It’s going to be up to me to figure out what it means for understanding the geological history of the place I live in the Rio Grande rift valley.

Tertiary Hill

On the way back from the barbarian’s wash I noticed a hill that had grass growing at it’s base, but was bare at the top. Oddly it supported several junipers.

The slope wasn’t steep. Up I went.

The grass gave way to what looked like caked mud.

Only it wasn’t. I picked up a piece. It was thin rock of no particular distinction.

I continued to the top where the fragments began to take on the shape of some kind of flow over what must have once been soft mud.

If the washes were slowly revealing some previous landscape, this hill top represented how deep those sediments must have been. Presumably, the land was all at this height at some time, but the rock kept this from being eroded as completely.

The junipers had found their water beneath the slabs.

When I got home I discovered the nondescript rock wasn’t some piece of rough-textured sediment, but a slice of conglomerate, I assume from the Tertiary age. How it got atop the sediments is another mystery, if indeed the sediments are younger.

Black Mesa

It seems, wherever you go in this part of the world, you find a Black Mesa. It shouldn’t be surprising, really, when you consider the Rio Grande crosses an oblique line of volcanoes.

There are two in this area. North of town, the ten-mile long finger of land between the Rios Grande and Chama has been called the Black Mesa by geologists since George Wheeler named it so in 1876. Down on the San Ildefonso grant near the road that people use to commute between the valley and Los Alamos there’s another, rising 500' from the surrounding flat lands that slope to the river.

When I first moved here, I was told or read the San Ildefonso mesa was the cap of the Valles Grande volcano that had landed there when it erupted. I’ve also been told it was the last retreat of the pueblo peoples fighting Diego de Vargas in the entrada and that there’s a pair of peregrine falcons nesting there.

Ted Galusha and John Blick resolved the ambiguous naming problem by calling the San Ildefonso mesa the Round Mountain. I prefer to find another name for the peninsula of land, perhaps Wheeler’s Black Mesa or the Chamita Black Mesa.

They also dispelled any romantic notions about its origins.

It’s an independent cinder cone built around a volcanic neck that was formed some 4.4 million years ago in the early Pliocene, possibly as part of the Cerros del Rio volcanic field southeast of the Otowi bridge. According to Daniel Koning, one of its lava flows has been dated to about the time the Rio Grande was becoming a perennial river, long before the Toledo and Valle Grande eruptions.

The base is dark gray to black basalt. The top is covered with river cobbles and pebbles laid down about 1.5 million years ago, long before the lakes described by Steven Reneau and David Dethier.

Cinder cones are the simplest type of volcanos, central vents surrounded by fans of erupted debris. Volcanic necks are formed when the magma hardens within the volcano. Red cinders found on the southwest side suggest an eruption was through that side.

When water washes away the softer materials that surrounds a volcano, the basaltic blocks drop into a dense mass around the base that eventually prevents further erosion. If indeed this volcano was standing in 500' of water in the early Pleistocene, there was a great deal of water available to consolidate the current formation into a fortress which has since survived those lakes and, perhaps, created the fans where juniper now grow.

Top: Black mesa behind cottonwoods along the Rio Grande taken from the west side along route 30.
Bottom: Mesa taken from northeast; the ranch road wanders towards it after leaving the far arroyo.

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.

Santa Fe Group

Santa Fe Group is a term like sparrow or hummingbird. It allows you to describe things fairly accurately when, in fact, you don’t really know enough to be specific.

Ted Galusha and John Blick say that at one time or another it’s been used to describe almost anything along the Rio Grande. They narrow the term to middle Miocene and early Pliocene sediments found between the Sangre de Cristo and Jemez.

They identify two general areas, one they call Chamita, the other Tesuque. Within the second, which is the one found where I live, they identified five major strata: Nambé, Skull Ridge, Pojoaque, Chama-el Rito, and Ojo Caliente sandstone.

The laminated formations you see along 285 when you drive through Arroyo Seco between Santa Fé and Española are from the Skull Ridge and Pojoaque members. According to Daniel Koning, the first was deposited 16.2 to 14.6 million years ago; the second is dated between 14.6 to 11.6 million years ago.

Koning also indicates that rocks came from two sources in the late Miocene. Those towards the north and west are from the Peñasco embayment between the Picuris and Santa Fe Ranges of the Sangre de Cristo, while those to the south and east generally arrived from the Santa Fe Range.

The Los Barrancos fault zone runs to the west of the highway. Sediments to the east, the ones you see, are older than the ones to the west, which are the ones that come close to my house.

The rocks on the west side of the road in the top picture are from the Peñasco embayment with the Skull Ridge member exposed in Arroyo Seco. The rocks on the east side in the second picture have the same provenance, but are older.

The third picture was taken on Pojoaque pueblo land. Koning identifies them as Skull Ridge layers from the Santa Fe range. In the picture below rocks from the Pojoaque member of the Peñasco embayment rise behind the wall of the far arroyo.

Lakes

The morning of the day the Las Conchas fire started, the air was so hot, the soil so dry I went looking to see if any prickly pear were blooming anywhere this season.

One place I walked was an open field just beyond the near arroyo. Nothing. Not a flower, hardly a healthy plant in a place they bloom year after year.

The Pacheco fire was still burning towards Tesuque and was sometimes visible from the road in the area. I looked that way from somewhere in the center of the field and, besides smoke, saw something I’d never noticed before. The field looked like a great bay that water had washed over from a break in the badlands.

Saturday, when I was in the near arroyo, I wondered how it connected to that open space which it had to border somehow. The bed narrows between five or six foot walls a little beyond the point where water begins channeling itself for the culverts. As I went up stream from there, it turned to the left and suddenly opened into a great, wide expanse with almost no banks.

I remembered something similar in the far arroyo. Yesterday I walked back to refresh my memory. Again, the tall walls make a turn, this time to the right, and a great expanse opens.

I came home to pour over Daniel Koning’s map of the Española quadrangle and I noticed something I’d missed before, that some of the places I’d read as Qay1 were really Qayi.

Qay1 is his code for alliuvial soils laid down in the first phase of the post-glacier Holocene period. The river bottom is Qay2, a younger layer.

Qayi turns out to be some intermediate phase of sand and gravel bands, the very strata I’d noticed along some of the taller walls in the far arroyo. The same pattern appeared in the shallow walls of the great expanses of both arroyos. This is precisely where he’d marked Qayi on the map.

Some passing reference in Ted Galusha and John Blick’s article on Española sedimentation that I’ve slowly been reading sent me to look up the Otowi lava flows they said had dammed the Rio Grande in recent times.

I discovered Steven Reneau and David Dethier’s work on area lakes created when landslides dammed the Rio Grande around the Otowi bridge. One occurred around 43 thousand years ago and created a lake some 15.5 miles long that lasted anywhere from a hundred to a thousand years.

Another landslide created a pool 13 miles long about 17.5 thousand years ago which broke suddenly. The most recent, formed about 12.4 thousand years ago, was also about 15.5 miles long and filled completely with layers of sediment.

During much of this time, the very end of the Pleistocene, there was greater rainfall than now, so the river levels would have been higher. The most recent lake was 100' deep.

This area is well within 10 miles of the Otowi bridge, probably much closer if you’re a crow or a drop of water.

One small mystery has been solved, the origin of those gravel bands. What still is unknown is why the channels that are being opened now in the arroyos and washes were there to be filled by Qay1 and Qayi in the first place.

The Cone

This afternoon I went back to the cone, determined not to be fooled again by its wiles. This time I took the simple path, the one from the near wash. As I walked up the easy grade, I realized the cone might just be the tip of the hill I live on, the one that had caused so many water problems in the past.

As soon as I got close I saw that it wasn’t bare because of erosion caused by the ATV rider. It was actually stone and not some soft soil. Daniel Koning had said it was tertiary, not the more recent quaternary. The two were there to see on the slope where the grass couldn’t hold its own.

I started climbing the cone. The more I climbed, the more the top receded into a face of gravel.

I felt no overwhelming urge to make it to the top and yodel. My knees were chanting "Jack and Jill went up the hill." The view of the black mesa was quite spectacular where I stood.

On the way back down I picked up some pieces of the grey, rough textured stone for the Rock Queen.

Hopefully she can tell me what it really is, something more useful than tertiary side of the geological change.

The Wash

A bare cone stands back from the road, beckoning you to come discover. It’s sides have already been marred by ATV drivers who took the challenge. Yesterday, I heeded its siren call.

I was coming back from the near arroyo when I thought I spied a path to its base, a sort of gently sloping, lowland route. It had the right come hither look, a promise it wouldn’t be hard on the knees.

I started back. The grass covering disappeared to expose the usual tan sand and clay.

Then the bared ground turned into a dry arroyo, a wash completely hidden from the road.

The wash turned into a maze of washes that might somehow, if I followed the right one, lead me back to the arroyo.

The cone became harder and harder to approach.

I turned and found the wash also connected to one that crosses the county road close to my house. I chickened out and took the low road home.

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.

Arroyo Walls

Appearances are deceiving.

When you walk through the far arroyo, the walls on the one side are tall and furrowed like the sandstone you see in pictures of Egypt’s Valley of the Kings. On the other side are low, sloping banks.

You assume the first are more substantial than the second. Don’t bet your climbing knees on it.

The surface here is the ungainly named Santa Fe Conglomerate, a lamination of sand, clay, and gravel. If you paw at the sand-clay layers they crumble in your fingers. If you claw at the gravel it stays put until you increase your pressure.

The sculptured surfaces of the tall walls must be the result of constant wind action. When it falls, the rain pocks the skin, leaving small depressions. This year, soot from the Las Conchas fire collected on the ridges between.

The slovenly surfaces of the other result from rain which forms a glaze that resists the wind. When it washes out, however, it disintegrates faster than the clay it lay with. And, apparently when its surfaces can’t produce an adhesive, it leaches and, eventually, brings the clay down with it.

Ditch Head

Today I went searching for the ditch head that feeds into the far arroyo. Head may not be the right word for the boundary between man and nature, but it’s all I can think of for the terminus.

A concrete lined ditch sweeps across the land between the near and far arroyos, going underground where it nears a road.

When it reaches the last piece of land, a neck of concrete, so thin it resembles plaster, channels the water away from the owner’s coyote fence.

It’s path from there is obvious, its course marked this time of year by brilliant leaf colors. There’s a long drop into a dry pool where water collects briefly.

What’s interesting is that after the drop the water’s route is no longer directed by the actions of humans, but follows ancient soil patterns.

The area lies on a long downward slope that angles south and west. The surface is crossed by ridges and valleys going roughly east-west. When nothing has disturbed the land, all’s covered with bunch grass.

When a low place is created in the land, perhaps by a road cut or ATV tires, water has a new path. The softer soils absorb more of the water than the harder ones. They are dissolved from the developing walls, fall into the bottom, and are carried away by wind or water.

The harder soils stay longer, creating what look like eroded craters.

The acequia water, which runs most of the summer, apparently lapped into soft spots of soil along its course that then began washing out. There are two major gullies uphill from the main water path. As they near each other and the main ditch path, they remain separated from each other by harder land.

The harder land looks much like the hard walls in the arroyo, and like those it doesn’t support as much vegetation as the softer soils that are eroding away.

The thing that has always surprised me about this man-made feeder to the arroyo is that it ends so abruptly that it endangers the houses near it. It’s hard to tell without digging before you build if a particular section of land here is on hard ground or soft.

The acequia association probably had no choice. After years of land disputes, and I suspect these particular houses, as well as mine, are sitting on some land grab, the pueblo probably wasn’t interested in making any more of its land attractive to interlopers and simply said no.

Unfortunately, no is not a word water understands.

Pictures top to bottom: 1 - ditch just outside the last fence. 2 - ditch as seen through the last fence. 3 - ditch from bottom looking up at same fence. 4 - land from across the ranch road; the white shed left of center is next to the arroyo terminus. 5 - the current end of one of the wash outs feeding into the ditch path. 6 - two wash outs separated by a spit of land; the cottonwoods to the right mark the main ditch path. 7- wash out between #5 and #6 showing bare hard rock and colonized softer soil.

The Far Arroyo

I live between two arroyos, each about a quarter mile from the house. The one to the north I think of as the near arroyo because I cross it every time I drive into town. The other, to the south, I think of as the far arroyo because I have to walk across pueblo land to get to it.

The far arroyo changes its character every fifty or a hundred feet, partly because of humans. At the time the USGS map was revised for this quadrangle, the local ditch emptied into the near arroyo.

At some later time, a pipe was installed to carry water across the arroyo and out to the land downhill from me. A neighbor told me the land under his house and mine were once part of a ranch, perhaps the same one that survives beyond the arroyo. The acequia extension dumps as soon as it reaches pueblo ground.

The water has cut its own path to the far arroyo. From a distance it can be followed by the trees that grow along the banks, including those yellow cottonwoods pictured in the previous entry. The above picture was taken from the arroyo at the point where the acequia water is heading its way.

Thursday I walked down the arroyo to the point where the acequia feeder enters the arroyo. At that point the water has cut a path not much more than a foot deep.

The water flows immediately to the right where it has cut through the soft bottom land. The sand and clay wash away, leaving a path of gravel, the generic Santa Fe Conglomerate that covered this area before the rift opened.

The soft soil absorbs water from both the air and the arroyo, which makes it more likely to crumble. The water band hasn't quite evaporated in the picture below.

The water apparently eats back through the soft soil under harder upper layers, until they collapse from lack of support. The water line under the rock can be traced by the appearance of Russian thistles that find enough sustenance to germinate in late summer on the downfall that flares from the bottom.

The arroyo widens and deepens where some previous geological event created the layers of hard rock.

Then, when the hard rock ends, the wall abruptly stops and the arroyo returns to bottomland vegetation.

That’s the point I turned back Thursday.