Santa Fe Group

[I originally wrote this in November 2011, but never posted this series on the local geology. The pictures are still worth seeing.]

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 generally towards are south and east 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.

Galusha, Ted and John C. Blick. Stratigraphy of the Santa Fe Group, New Mexico, 1971.

Koning, Daniel J. Preliminary Geologic Map of the Española Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico, 2002, map and report.

Mastodons

[I originally wrote this in November 2011, but never posted this series on the local geology.]

The first time I heard of a mastodon I was sitting in a lecture hall at Michigan State listening to Russel B. Nye, who often combined cultural history with American literature.

I don’t remember what he said beyond a nearly complete skeleton found in Ohio had caused quite a sensation in the early nineteenth century. Somehow, I got the idea the skeleton was lying, fully exposed, on top of the ground and was stumbled upon much like the mounds had been.

I’ve since heard the animal was a glacier age mammal hunted by people using Clovis points. For some reason, that led me to think of them as great grass eaters.

When one’s interest in a subject is superficial, one’s knowledge tends to become a brew of facts, romantic legends and false conjectures.

I was, understandably, quite startled to find someone I think was Francis Klett say:

"In these beds, near Ildefonso, I made some excavations in 1873, while on the way to Fort Defiance under your expedition, (division 2,) and brought to light fossil bones of a mastodon, only one of them perfect, however; others were broken and yielded but fragments."

The quotation is from the 1873 Annual Report of George’s Wheeler’s Geographical Suverys West of the 100^th Meridian, and the location must be somewhere just north of route 502. That’s almost as close as the Otowi Bridge.

I suddenly needed to know more about mastodons. As I read, accretions of secretly hoarded facts dissolved.

It was true mastodons were glacial creatures and had been found in association with Clovis points.

However, they were associated with cold spruce woodlands, not grassland refuges.

Spruce growing where grass has been having a hard time this year surviving a drought.

Spruce near the Otowi bridge when those boulders blocked the Rio Grande creating lakes.

Spruce along those arroyos with the Qayi late-glacial sediments identified by Daniel Koning.

Spruce in my backyard. Who cares about a mastodon eating the foliage. Cold climate spruce right here where I’m writing.

Spruce.

Lakes

[I originally wrote this in October 2011, but never posted this series on the local geology. The pictures are still worth seeing. The Las Conchas fire burned through Santa Clara canyon that summer.]

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 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.

Galusha, Ted and John C. Blick. Stratigraphy of the Santa Fe Group, New Mexico, 1971.

Koning, Daniel J. Preliminary Geologic Map of the Española Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico, 2002, map and report.

Reneau, Steven L. and David P. Dethier. 1996. Late Pleistocene Landslide-dammed Lakes along the Rio Grande, White Rock Canyon, New Mexico.

The Cone

[I originally wrote this in October 2011, but never posted this series on the local geology. The pictures are still worth seeing.]

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 already making threats. The view of the black mesa was quite spectacular from where I stopped.

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.

Daniel J. Koning. Preliminary Geologic Map of the Española Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico, 2002, map and report.

Soot

[I originally wrote this in October 2011, but never posted this series on the local geology. The pictures are still worth seeing. The Las Conchas fire burned Santa Clara canyon in 2011.]

This morning I walked to the far arroyo for the first time since Wednesday’s rain. Everywhere there were signs of the Las Conchas fire.

When I entered below the ranch road I saw black soot laying in water paths left on the bottom.

As I walked up stream I saw the charcoal trails along the low left banks. As I came back down, they were also on the right side, swirling along the base of the high walls.

I could only think it’s a Goldilocks situation. Earlier this summer, when water scoured the bottom of the arroyo, it was passing through so quickly it left little behind. Other times, the rain was so gentle it only moved silt a few feet. The traces of black were slight.

Wednesday it rain most of the day and much of the night, a gentle rain that soaked in. I’m guessing that it washed a layer of sand from the surface of those blocks I noticed earlier where it had accumulated and the soot and sand landed somewhere down stream.

Upstream, there must have been other patches of ash waiting to move. Each time this year when some ash moved from higher up the arroyo, it replaced some that had been washed down stream. Perhaps it had slowly become concentrated in areas near the main water paths. Finally, there was enough rain to collect it and move it slowly where it could drop between Wednesday’s showers.

The fire was suddenly visible everywhere again.