A Watershed

Sometimes a watershed is more than a parting of the waters.

This week I drove southeast from Santa Fe toward Clines Corners on route 285. After passing the rump end of the Sangre de Cristo, the road passes through the Galisteo basin where grasses spread from both sides of the road.

Then, volcanic debris reappears with juniper trees. I stopped somewhere near mile marker 268 where an open expanse of four-winged saltbush outlined what must have once been flood land.

Snow from last week’s storm still veneered the land, but didn’t cover the taller plants. A few black cattle were visible in the distance. It was considered range land.

Just a few miles down the road glazed snow spread to the horizon. Shrubs were half-buried. The wind picked up. Just beyond Clines Corners plows were out keeping the right lane to Vaughn cleared from blowing snow.

When I drove back I noticed a sign somewhere between the two points where I’d stopped to take pictures that indicated I had crossed into the Galisteo watershed.

Apparently, this didn’t just mark the boundary between the volcanic Rio Grande valley and the great plains. It denoted a change in climate as well.

Pictures taken 29 December 2011 on route 285. Top taken about mile marker 277. Second around mile marker 268. The others near mile marker 263, less than five miles away.

A Rock Is a Rock Is a Rock

The young man in the mineral shop who dismissed my gray rock as “just a rock” with none of the special characteristics of a recognized mineral was wrong.

Rocks aren’t just rocks. To begin with, there are only eight elements that go into the composition of most: oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium. They represent great permutations on matter.

Basalt is some combination of oxygen, silicon, aluminum, calcium, sodium and magnesium. The percentages of silicon and sodium are often used to define the type.

Granite is formed from magma and contains oxygen, silicon, aluminum, sodium and potassium.

Quartz is essentially oxygen and silicon.

Rocks don’t limit themselves to just the eight fundamental elements. Basalt, pyroxene and perovskite can contain titanium. Zircons are silicon and oxygen with zirconium.

More important for geologists interested in the history of the planet are their trace minerals. The half-lives of radioactive isotopes of elements like uranium, neodymium and samarium are used to date them. Zircon crystals are the oldest found above ground.

Rocks, as pieces of matter, do have definable characteristics. In the early twentieth century, Norman Bowen crushed them so he could heat the powders until they melted, then heat them more until they boiled. He let them cool in controlled steps.

He ended with iron-magnesium bearing olivine which was formed at a high temperature and pressure. At a specific lower temperature it becomes pyroxene. At another temperature, pyroxene becomes amphibole, and that, in turn, becomes biotite. In contrast, plagioclase gradually transitions from a rock rich in calcium to one rich in sodium without the abrupt phase breaks.

At a set point, they become potassium feldspar, which becomes muscovite, which becomes quartz. These are the three major components of granite, with quartz the least likely to weather away because it was formed in conditions closest to those of the present.

In the past few decades, new technologies like diamond-anvil presses have allowed geologists to return to experiments like those of Bowen, only now they are looking at how rocks are altered at the higher pressures and temperatures deep in the mantle. Instead of changes in elemental chemistry they’re interested in changes in crystalline structure.

When pressure increases, the O^2- ions in olivine are altered into a spinel structure. At even higher pressures, the spinel structure converts to one found in perovskite and another found in periclase.

Near the earth’s surface, enstatite combines silicon, oxygen and magnesium. It too converts to a perovskite-like structure at higher pressures, then near the bottom of the lower mantle to a post-perovskite structure.

All of this makes terminology a bit confusing, since the same thing is identified by its elements, its crystalline structure and its origins. What one thought was just a rock isn’t. There are at least 11 forms of olivine, including basalt which is further broken into five groups. There are 24 types of pyroxene, including enstatite, and 37 varieties of mica, including biotite and muscovite.

It doesn’t help that only some of these can be seen. Anything with a post-perovskite structure immediate changes to something else when the pressure relents which it must if it’s to make a journey from the center of the earth where it may end up as simple quartz in my arroyo.

Mica (top) from near Albuquerque; granite with bands of gray quartz and shining specks of mica (middle) and a thin piece of quartz (bottom) from the far arroyo.

Quartz

My bookshelf is beginning to resemble something hidden in the backroom of a museum. Sedimentary rocks kept from crumbling on my floor lie in baggies. None are particularly attractive. They simply will be informative if I ever put them side by side to learn the differences in the different sediments in this area.

My camera doesn’t like any of them. I fantasize about the silicon chip rebelling at such ugly dates and give it nicer silicon oxide to look at.

White colored quartz is common in the arroyos, usually as pebbles, but sometimes in larger hunks. But more aesthetically pleasing are the small, broken ones with exposed facets that capture light.

The Ways of Water

On my way back from the Barrancos I followed the path left by water. This was less a point of curiosity than the easiest way to negotiate broken land. The rivulet began somewhere in the hillocks below the fan before the cliffs.

From there the water wound through low hills.

The water reached more gently sloping ground, where its path was marked by the lack of vegetation. Once in a while, the bottoms was littered with gravel it had recently picked up, but mainly it was a slightly shinier, more level continuation of the banks.

When it reached a more level area where sedimentary gravel covered the ground, it spread wider. Juniper trees grew along both sides.

Below the junipers softer soils appeared. The line was crossed between Tertiary and modern alluvium. Water was no longer able to define a specific course. It spread into a flood plain, leaving areas bare of vegetation. The only clues for where water had flowed were gravel deposits.

The water was flowing generally northeast toward the arroyo when it collided with an ATV trail headed straight for the north end of the cliffs. The water ricocheted back. It was lower than the trail.

From there it ran parallel to the ATV track, preternaturally straight. Its depth varied with soil. When it found something soft, it was deep. One time it was deep, a wash was opening on the other side of the track. At another point the banks were caked with grey mud.

When a particular grass was resistant, it disappeared in the shadows.

When it encountered another channel coming from the southwest, it got lost in another flood plain, until the channel reformed next to the ATV track.

The pattern repeated itself: a straight run, a collision with another water stream, a confused path, rationalization along side the higher road.

Then, a competing channel came through at just a point in the descent where the ATV track was nearly level with my water path. The abutting channel swept across the track, pulling my stream in its wake.

An arroyo feeder formed in the softer soils, twisting and turning around small changes in the earth. Sometimes, one side was steep and the other a delta; it other places the sides were the same. It behaved again like one would expect water to behave.

Just before it reached the arroyo there was a small washout, perhaps formed when water was backup during a storm by stronger currents in the far arroyo.

The feeder entered the far arroyo downstream from where the ATV track began. The water dropped its final load of stones as it changed course when it met the passing waters. From there it flowed towards the Rio Grande.

Valley of the Arroyo

Yesterday I walked to the closest Tertiary formation in the Barracanos badlands. From the base I looked back towards the formations on the other side of the arroyo. A valley I’d never recognized spread out below. The arroyos and washes that dominated when I was in the valley had disappeared.

A few days before I’d walked downstream along the top of the left bank between the ranch road and the area widened by the irrigation ditch. In that small area I could see the level I called the second bottom existed on both sides and appeared to be the same height.

This isn’t a glimpse of the Tertiary past. Rather, this is what remains after waters filled, then retreated, waters that rose to different heights at different times.

Note: Picture 2 is looking down on the second bottom. In picture 3 the bottom continues on the opposite side in the space between the two bare banks.

Earthly Beginnings

The early history of the earth is more theory than fact, and those theories are taken more from astrophysics than other disciplines. Those with other interests tend to pick through the available information in hopes of arriving at some early history for their subject.

A great many look for the thread that explains the origin of life. Others want to know how the moon was made.

My focus has been the creation of the conditions that made possible the emergence of that part of the North American plate where New Mexico sits between 1710 and 1600 million years ago, with a certain inclination to pay some attention to the formation of Michigan, the state where I was raised.

For me, this means envisioning how a 4600 million year old cloud of gas and dust evolved into a stratified ball whose layers have been defined by the workings of heat and cold.

The most important element has been iron. According to Wikipedia, iron begins in stars hot enough to burn silicon and initiate a chain of reactions with helium that transform matter from silicon to calcium to titanium to chromium to an unstable iron. That iron fuses with a helium nucleus to create ⁵⁶nickel, after which the star collapses and the ⁵⁶nickle transforms into ⁵⁶iron via ⁵⁶cobalt.

During the earliest millennia of the planet, radioactive decay continued in particles of nickle in the cloud which created conditions warm enough to heat the iron dust whose melting point is 1535 degrees centigrade. Following one basic law of physics, liquids are heavier than gases, the molten iron would have begun to isolate itself from the heat generating gases.

As it moved away from the source of heat, the molten iron would have gone through several structural phases. When the temperature fell below 1540c degrees, it would have begun to solidify and at 770c degrees it became magnetic.

Following another simple rule of physics, heat rises and cold falls, the cooler materials would have drifted towards the center of the ball, and the gases remained on the surface. Once enough iron had fallen below 770c degrees, the magnetic core could form. This process took about 50 million years and was complete around 4535 million years ago.

Once the nickle and iron coalesced into a ball divided into two parts, the magnetic, solid inner core and the molten outer core where temperatures today range from 5000c to 2200c degrees, silicon, magnesium and similar elements were segregated into an outer layer. Steve Kershaw suggests the mantle emerged around 4000 million years ago, and that it took about 2000 million years for the separation to be completed sometime around 2000 million years ago.

While the interior was still evolving, the outermost layer cooled into a skin that became the precursor of the crust. The oldest rocks found so far on the North American plate are from the Nuvvuagittuq greenstone belt near Hudson Bay. They are estimated to be between 3800 and 4280 years old.

The skin created a barrier between the warmer interior and the lighter gases which allowed water to condense without turning into steam. Oceans existed more than 3900 years ago, according to Kershaw. Scientists argue whether all the water was native or was increased by collisions with meteors and comets which could still easily penetrate the surface gases.

At this point, the history of the earth diverges into four separate narratives - the mantle and its skin, the oceans, the gases, and the crust and its plates - which rejoin sometime before New Mexico makes its appearance on the stage.

Notes:
Chandler, Harry. Metallurgy for the Non-Metallurgist, 1998, on properties of iron.

Kershaw, Steve. “Precambrian Ocean Change” in Oceanography: an Earth Science Perspective, 2000, with contributions from Andy Cundy.

Wikipedia entries on Earth’s history and iron.

Ranch Animals

Last week I returned to the washes that lay to the right when I was following the road south of my fence. The thing that originally struck me was that the wash stopped at the fence that marked the boundary with pueblo land.

I couldn’t see how nature would respect mere strings of barbed wire and sapling posts. I supposed it was possible, given the way the land varies, that whoever claimed land out of the pueblo grant followed some natural indicator, say the variety of grass which reflected something about the underlying soil structure, but I really couldn’t credit the idea much.

I turned to follow the fence towards the arroyo and found something strange. Maybe ten feet to the side of the barbed wire boundary was a line of farm fence topped by several lines of barbed wire creating a sort of no-man’s land between. The gully began at the farm fence post.

The lane ended abruptly with a line of barbed wire cutting between the two fences and a wash that made it nearly impossible to walk by. The boundary fence continued to the arroyo; the farm fence stopped. It could have been some kind of animal enclosure, but I couldn’t really see what or why.

Yesterday, I went back to the near arroyo to follow the right bank back to the cactus field. The arroyo maintained its lake like appearance on this side of a barbed wire fence marking the pueblo boundary.

I followed the bank back to its farthest corner where I found the remains of wooden chutes used in some way to corral animals. If the current width is any indication, it was probably sheep rather than cattle.

There had been similar remains on my uphill neighbor’s land and in the barbarian’s wash near the road, but they’ve since been cleared away.

As I looked out over the land, the eroded gullies were, for the most part, limited to the private side of the fence like they were further south.

I now wondered exactly what animals could have done to precipitate the natural forces that were uncovering the older landscape. If the contours existed then, I suppose they would have followed the valleys were grass might be lusher and eaten the ground bare, leaving it open to wind and water.

I suppose it’s also possible that the softer spots in the land caved under their weight, and those low spots became the targets of the weather. Between the gullies, the land remains grassy knolls that hide the open trenches. The steppe scrub that returns with overgrazing appears in limited patches in the washes and nearest the road and ATV trails.

Another Road, Another Wash

A road branches to the west from the ranch road just below my fence. It was always there in some form, but some years ago some trucks came through and made it more obvious.

At the time someone told me the Indians did it to get back to some clay deposits they needed for their pottery. The person who told me was simply passing on something he’d heard. However, it sounded like one of those things you’re told by people who are aware others exist in the universe who live differently than they, but don’t actually know any of them and so attribute everything to them in an almost conspiratorial fashion to establish they really do know what’s going on.

Another possibility was that some utility had to get back.

The one thing it wasn’t was an enlightened county project to build a recreation trail. However, that’s how it’s been used since by those who walk their dogs or their hearts. The trucks haven’t been back, but it’s been kept open by ATV’s.

It never seemed particularly interesting to me, because I’d already learned few wild flowers grew with the prairie grasses. The far arroyo was more rewarding.

Yesterday was the first time I walked farther than the junipers.

A wash opened on the right that wasn’t connected to the one that had backed up from the acequia drop. The ranch road goes between the two with no sign it’s been filled. Still this wash looked like it might be part of the same weak area.

The banks were steep and maybe 8' high with isolated tongues of soil in the center. It went back as far as a fence and stopped, for no apparent reason.

I didn’t go in to explore. That was the adventure for another day. Today I wanted to know where the road went.

The fence wire had been removed between three posts for the road, which continued to climb toward a row of utility poles. It got to them, and continued to the left, which would be north. So much for that theory.

It rose to a crest, then dropped into a wash, this one the upstream section of the one by the cone I call the barbarian’s wash for reasons best left to the imagination. It had the same characteristics as the one to the south, steep banks and chiseled islands.

There were no signs anyone had mined the area, only that ATV’s had been through on their way north along the front of the tertiary uplands. So much for the theory it led to a special deposit of clay. It was simply a trail.

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.

Gravel Heap

As I got nearer home, a line of bare dirt caught my eye. It appeared to be a berm outlining a square filled with piles of gravel.

The imagination can come up with explanations besides a geometrically obsessed gopher.

It looked a bit like an archaeological site that had had a layer removed and sifted. However, I doubt any archaeologist would do the sifting within the confines of an excavation.

Another possibility was that it had once been a much taller pile of gravel, perhaps like the cone, and someone had sieved it to take away the finer stones for a road or drive. They may have built the berm to keep the rock from sliding away. However, I can’t imagine why they would have bothered to create a square, rather than an encircling ring.

It remains one of those inexplicable marks humans leave on the land that the weather hasn’t yet erased.

Ranch Road

Yesterday I walked out the ranch road towards the Black Mesa. I went as far as the pueblo boundary where it branches, with one prong going through a gate to the ranch and the other through an arroyo and on toward the mesa.

The road looks and feels like the arroyo bottom, but the neighboring soil is the usual erodible mix of clay and sand. When you get to the Y, the road on pueblo land becomes two tracks of uncovered dirt that would be difficult for a car to negotiate in wet weather.

As I walked back on compacted soil veneered with fine gravel, I wondered if the ranch owners had dredged the bottom of the far arroyo to protect their road, and if others had also done that in the past here and in the other arroyos.

If that were true, I wondered if the arroyo bottom had once been filled with gravel, had been bare like it is now, or had once supported vegetation like the arroyo on pueblo land. I also wondered if their mining had widened or flattened the bottom, or if the general shape had been carved by nature and only slightly been modified by them.

Bottom photograph shows the land to the side of the road, taken when I stopped to take the middle picture of the road where I kicked down to expose the base. Top shows the unimproved road on pueblo land.

Wind

Wind and water together sculpt the land. The effects of water are to be seen everywhere land appears more level than normal. Wind preys on spaces between bunch grasses and shrubs where soils dry.

Saturday the Rock Queen and I went driving west from Albuquerque in search of agate, oblivious to the winds that had developed in the city after rain had moved through there in the morning. Let it not be said that a rock hound can be deterred by mere weather.

We first noticed a completely bare hill on the south side of I-40 where dust was rolling a few inches above the surface like water rippling over flat stones in a rapids. We dismissed it as the work of man, for that hill had not a sprig of vegetation.

As we continued west, the winds grew stronger. The trucks slowed. The land alternated between fields of bunch grass, exposed layers of sediment, mesas and fragments of dark lava. The sky was only occasionally blue. Even in places where vegetation exists, a fog of dust crept a few feet above the surface, moving in, out and around high points.

We stopped to look for rocks near some odd formation that was near valleys that fed a lowland in a pattern of receding herringbones. On the leeward side where no wind could reach us, the surface of sand was frozen in inch-high waves from some previous wind. Whatever vegetation that had existed there had not survived the drought.

I’ve lived through sand storms in Abilene, Texas, where the dirt was so dense, you had to close your eyes to protect them. Grains got into you teeth. The paint on the car was blasted.

But those storms didn’t have the animate form the winds did yesterday outside Albuquerque. They were simply sheets of dirt moving through, often dense enough to turn the sun silvery at noon. They had none of the sinuous form of tunnels and layers that glided around mesas and outcrops.

The desolation the universe can create was on full display, but jasper littered the ground.

Note: Pictures are dark because I didn’t set light openings correctly on the camera, not because the sand blocked out the sun like it would have in Abilene.

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.

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.