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San Ysidro Anticline: Where the Colorado Plateau Meets the Rio Grande Rift

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We're about to hike along the south rim of what geologists call the San Ysidro anticline, or alternatively the Tierra Amarilla anticline. Trail bikers call it the White Ridge . Millions of years ago, things looked quite different here: we're peering into a valley that was a ridge, not a low point. The peak of the ridge followed the center of the valley you see here - so the highest part of that ridge is now the lowest part of today's valley. Geologists call this "inverted topography": the highest parts of the land have been transformed into the lowest parts. How did that happen? The rock layer that covered the top of the ridge was made of shale, limestone, and gypsum. You can see the white gypsum on the trail at the edges of this photo (geologists call it the Tonque Arroyo Member). This hard rock cover was eroded off the top of the ridge by wind, precipitation, and freezing and thawing. As it wore away, much softer sandstones, mudstones, and siltstones beneath ...
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Casamero Pueblo: Caught in the Owl's Eyes Gaze

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Casamero Pueblo is a Chacoan outlier Great House site located between Grants and Gallup, NM. This two-story Great House was occupied between A.D. 1000 and 1125. It had 22 ground floor rooms and may have had six second-story rooms. It is located 45 miles south of Chaco Canyon, making it a Chacoan outlier community. You can see its walls in the far distance, to the right of the sign, at the base of the bright red sandstone cliffs of Tecolote (Owl) Mesa. The two alcoves just to the right of the sign form the large "owl's eyes" that give the mesa its name. The Great House had T-shaped doorways that are characteristic of Chacoan architecture, one small interior kiva, a great kiva, and two Chacoan roads. Casamero was settled during a time that corresponded with a surge of building in Chaco Canyon – around A.D. 1050. It existed during much of the florescence of Ancestral Pueblo culture in Chaco Canyon, was clearly related to it, and declined in unison with it. When something in...
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Arroyo Negro Pueblo: In My Backyard

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For several years, I tried to pin down the location of the site of a 1,000-year-old Pueblo village that was supposed to be near my home. Eventually I found it, just 600 feet from my backdoor, on top of the ridge that you see in the background of this photo. This view of the ridge that climbs about 100 feet above my house is looking from the rooftop of my house, and my neighbors' houses. This pueblo was first excavated by archaeologists in the 1920s, who named it the Arroyo Negro Pueblo. It is considered perhaps the best mapped, although least described, of the Santa Fe River pueblo sites from the Late Development period. Wood cores were taken from structural support timbers of the buildings in 1934 to do tree ring dating. The Ancestral Puebloans spent 50 years constructing seven buildings up there, from the years 1050 to 1100. The buildings consisted of anywhere from 2 to 25 rooms. Alongside most of the buildings, on the side facing the Santa Fe River, was a round, free-stand...
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