Geology of Madrid and the Cerrillos Hills - Part 3

(Make sure you read Part 1 & Part 2)

I know what you're probably thinking, "All this magma this and Christmas tree that -- whatever. You're talking about the Turquoise Trail - what about that TURQUOISE?!"

Okay okay, settle down. Time for the turquoise.

[flickr-photo:id=5350115058,size=m,class=float-left]The volcanism of the Cerrillos Hills area doesn't end with Christmas tree laccolith. A few million years after the volcanic activity that formed the Cerrillos Hills and the other nearby mountains (around 30 Ma), another round of activity occurred. This round is related to the beginning of the Rio Grande Rift Valley, and involved the earth's crust stretching out. With the earth pulling away in the Rio Grande Rift, the stretched & weakened rocks allowed the magma to the surface, where it magically becomes lava. The lava that made it to the surface has all eroded away, but what yet remains is the magma-to-lava conduit system, or dikes. Dikes are a vertical version of sills - igneous rock that moved up across the grain of the existing sedimentary rock.

Even after the dikes were formed, they still were changing the geology of this area. Since it's insulated within the crust, magma takes a long time to cool off. And while it's cooling, it heats groundwater. This super-heated groundwater dissolves minerals in the cooling magma. And when the cooling rock cracks a bit, the superheated water goes into those cracks. And as the water cools those dissolved minerals un-dissolved from the water, clumped together in the cracks of the rocks, and formed the veins sought by the miners. And what kind of minerals were deposited? Well for one, turquoise.

In addition to turquoise, the miners of Cerrillos have dug copper, zinc, and silver from the ground of the Cerrillos Hills. But now all the valuable deposits have been found, mapped, dug, and removed. Miners still have claims, and they still pull turquoise from the ground. But the majority is gone. The decline of the mining industry also marked the decline the towns of Los Cerrillos and Madrid. By the 1960's, both towns were on their way to ghost town status. But in the 1970s the tourist industry provided enough income to stabilize them. And now Madrid is a popular arts community, and Los Cerrillos provides the Western backdrop for movies.

So should you go? Yes, yes you should. The towns themselves are diverting enough for a day-trip. And if you know the geological story behind the area, you can spend a couple of days exploring.

Oh, and here's a map showing photos and geologic cross-sections that I referenced:

View Madrid - Cerrillos Hills Geology in a larger map

References and Further Reading:

Preliminary Geologic Map of the Madrid 7.5 - minute quadrangle by Stephen R. Maynard, David Sawyer, and John Rogers
(http://geoinfo.nmt.edu/publications/maps/geologic/ofgm/downloads/40/Madr...)
Preliminary Geologic Map of the Picture Rock 7.5 - minute quadrangle by Stephen R. Maynard, Alvis L. Lisenbee, and John Rogers
(http://geoinfo.nmt.edu/publications/maps/geologic/ofgm/downloads/51/Pict...)
Laccoliths of the Ortiz porphyry belt, Santa Fe County, New Mexico by Stephen R. Maynard (http://geoinfo.nmt.edu/publications/periodicals/nmg/downloads/27/n1/nmg_...)
The Geology of the Cerrillos Hills by Stephen R. Maynard
(http://www.cerrilloshills.org/nature/geosummary.html)
Under the Volcano
(http://innonthealameda.com/the-authentic-guide-to-santa-fe/2010/01/under...)