Southern Margin of the Marathon Basin

by bill macleod on October 21, 2009

Continuing down the Marathon Basin on Hwy 385, the southern margin on the left of the highway is seen in the above photograph, taken 24 miles south of Hwy 90. On this margin, the Cretaceous strata dip only very slightly to the south, perhaps because they are a distance from the center of the uplift. The knob in center is a small intrusion. Several similar intrusions occur along the margin.

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Santiago Peak

by bill macleod on October 16, 2009

A close-up view of Santiago Peak from the south, 50 miles down Hwy 385 from Hwy 90. The northeast wing of the intrusion can be seen from this angle, about 6,250 feet at the peak, 270 feet lower than the main body. The shapes of the two summits suggest that they are part of a plug, not an eroded sill. The flat top seen in the previous photo would therefore be the result of the uprising intrusion coming in contact with a resistant rock layer, perhaps a thick lava bed.

It is hard to believe that there were lava beds at this altitude when there are no traces of volcanic rocks of the main volcanic phase east of this point, but Elephant Mountain, 12 miles to the north is definitely a sill, the top of which is at 6,230 feet, so there has been a great amount of volcanic material removed in the last 30 million years.

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Flatirons

by bill macleod on October 13, 2009

Continuing down Hwy 385 in the Marathon Basin, one of the most spectacular sights are the flatirons on East Bourland Mountain, photographed 8 miles south of Hwy 90. A flatiron is a short, triangular hogback forming a ridge or spur on the flank of a hill that looks like a flatiron. A flatiron is usually a plate of steeply inclined resistant rock, in this case Caballos Novaculite, called a flatiron from its shape. A flatiron is a short, triangular hogback forming a ridge or spur on the flank of a hill that looks like a flatiron. Here, the light-colored flatirons of novaculite stand out against dark Maravillas Chert on the higher parts of the mountain. The Maravillas Chert Formation is of bedded black chert and dark gray to black limestone, 100 to 400 feet thick, the next youngest to the novaculite in the Marathon Basin succession.

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Santiago Peak

October 4, 2009

The other major landmark in the southern Marathon Basin is Santiago Peak (6,521 feet), seen here in a photograph taken 6.4 miles south of Highway 90. The peak is one of the most striking landmarks in the Big Bend, rising 3,250 feet very steeply the Maravillas Creek valley below. The upper part is a nepheline [...]

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Marathon Basin

October 1, 2009

Continuing my journey around the Marathon Basin, this photograph, taken one mile south of the Highway 90/385 junction, is a good illustration of the basin south of Hwy 90. Many of the hills there are capped by a chert bed known as the Caballos Novaculite, Caballos from Horse Mountain in the basin where the chert [...]

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Cathedral Mountain in the Glass Mountains

September 29, 2009

I have been taking photographs in the Marathon area in preparation for a small book on the basin. The original Big Bend Vistas had a section on the Marathon basin but I had to drop it in the Second Edition to keep the book down to an affordable size.
Cathedral Mountain in the Glass Mountains (confusingly [...]

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Chisos Basin

September 19, 2009

Chisos Mountains Lodge and Casa Grande (7,325 feet) in the early morning mist. Casa Grande is a square-topped monolith of bare volcanic rock with sheer, towering cliffs overlooking the Lodge some 2,000 feet below. The volcanic rhyolite dome capping the mountain is slow to erode, and forms solid cliffs. Below it, thinly layered surge deposits [...]

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Indian Lodge

September 19, 2009

Indian Lodge from below – the design is pueblo revival, something quite foreign to West Texas except though the work of architects like Henry Trost. The Civilian Conservation Corp, who built the lodge, employed its own architects, in this case Arthur F. Fehr, who also worked on restoring the San Antonio missions.

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Historic Fort Davis

September 18, 2009

This view of the old fort has Sleeping Lion Mountain (5,202 feet) on the left horizon with the buildings in front of Hospital Canyon and the columnar lava cliffs just coming into view on the right. The lavas are porphyritic rhyolite of the Sleeping Lion Formation, about 200 feet thick here. It erupted in a [...]

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West Alpine Basin

September 14, 2009

Ranger Peak (6,246 feet) on the left with Twin Peaks (6,133 and 6,112 feet) on the right, photographed yesterday on a beautiful fall afternoon. All three are igneous intrusions into lavas of the Decie Formation.
In mid-photograph, Lizard Mountain is another intrusion. For more see Davis Mountains Vistas.

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