The Taos Graben EarthCache
Hidden : 2/28/2010
Difficulty:
2 out of 5
Terrain:
1.5 out of 5

Size: Size: other (other)

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Geocache Description:



READ CACHE PAGE AND HINT

The Taos Graben is located in North Central New Mexico.

A graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. A graben is the result of a block of land being downthrown producing a valley with a distinct scarp on each side. Grabens often occur side-by-side with horsts. Horst and graben structures are indicative of tensional forces and crustal stretching.

Graben are produced from parallel normal faults, where the hanging wall is downthrown and the footwall is upthrown. The faults typically dip toward the center of the graben from both sides. Horsts are parallel blocks that remain between grabens, the bounding faults of a horst typically dip away from the center line of the horst. A single graben or multiple grabens can produce a rift valley.

Figure 1.)

The Taos graben, identified by geophysics and drillholes, is a buried, north trending, 13-km-wide, 5000 m-deep graben, and the major rift feature in the South San Luis basin.

The Eastern edge of the graben (Town Yard fault) lacks Quaternary expression, but is in line with the Picuris-Pecos Fault and the Questa section.

Conceptual geologic model of the Taos valley: The Picuris-Pecos and Sangre De Cristo are reactivated pre-Laramide faults. The Miranda and Taos grabens were originally parts of an oblique-slip Oligocene-to-Miocene basin. The Picuris-Pecos Fault and Questa section are the exposed eastern edge of the graben; Town Yard fault is the buried intermediate section.

Sometime after 4.5 million years ago, rift kinematics changed, and the EMZ-Cañon/Hondo section severed the Picuris-Pecos Fault, leading to its extinction.

The western border of the Taos graben is delineated by a gravity gradient line extending from 17 km north of Questa to the latitude of Tres Orejas. It is informally called the Gorge fault owing to its general coincidence with the extent of the Rio Grande gorge, where the river has carved a deep canyon through the basalts of the Taos Plateau. As the rift widened and extension slowed, the Taos graben was abandoned and faulting migrated eastward to form the Taos embayment.

This model explains many geologic, hydrogeologic and physiographic features of the Taos plateau, including the Rio Grande gorge, intrabasinal faults, Pliocene basalts, broad basinal warps, hot springs, groundwater flow and asymmetric drainages.

Standing on the Rio Grande gorge bridge looking north you can see the eastern and western borders of the graben. The western border is the Rio Grande gorge itself. The eastern border of the Taos graben are the Sangre De Cristo mountains.To get some really GREAT pictures of the Rio Grande Gorge, Travel to coordinates: N 36 28.583, W 105 44.118.

Figure 2. gallery Photo.



To Log this Earth Cache Visit the Rio Grande Gorge Visitor Center at coordinates. 36 16.057 N, 105 47.375 W

"Email the answers to me through my profile email, do not post them in your log." There is a Scale table model of the Wild Rivers Recreation area, answer these questions.
1.) What is the Scale of the Tabletop Model( The scale is not posted. You must make some measurements and calculations. Read the entire Cache page!!! at the Visitor center ?
2.) There are Five buttons corresponding to places in the recreation area what are they, and what are their posted elevations?
3.) What type of Faults produce Graben?

Post a picture of yourself and your GPSr at the model in the visitors center.
I have earned GSA's highest level:
"YOU MUST COMPLETE THE LOGGING REQUIREMENTS TO GET CREDIT FOR THIS CACHE. INCOMPLETE LOGS WILL BE DELETED!"

Additional Hints ()

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Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)

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