Ninth Santa Fe Conference on Rock Magnetism

Cerrillos Hills Road Log – Thursday 21st June 2012

Stop 1. Tour of the Cerrillos Hills State Park (Maynard, 2000)

1.3 mile hike from parking area to Mineral Spring that ends with water quality discussion.

Along the trail, we will have many opportunities to discuss the mining history as well as the bat

population that now resides in the abandoned mines.

Figure 1. View to the north towards Cerrillos Hills State Park.

Figure 2. Historical marker en route to the park on Main Street.

The Cerrillos Hills are a group of low mountains that covers an area about 18 square miles north

of the village of Cerrillos in Santa Fe County, New Mexico. The Cerrillos Hills Igneous

Complex is part of the Ortiz Porphyry Belt, a 40.2 kilometer long, north-south trending group of

intrusive and extrusive igneous rocks. The intrusive rocks can be divided into two main age and

geometric groups. The first is about 34 Ma and is composed of quartz-bearing andesite-latite

porphyries that was intruded as sills and christmas-tree laccoliths. At ~30 Ma, a series of quartz-

poor latite and monzonite bodies intruded the Cerrillos laccoliths as a series of dikes and plugs.

The change in emplacement geometry from sills/laccoliths to dikes/plugs is related to a transition

in the regional stress field associated with the waning Laramide E-W compressional regime at 34

Ma to a NW-SE extensional setting related to initiation of Rio Grande Rifting post 34 Ma.

Vein mineralization led to economical deposits of lead, zinc, gold, copper, and silver within

northeast-trending fractures shortly after the last stage of intrusive emplacement (within a million

years or so!). The Cerrillos mining district is known for its importance in the cultural

development of the region, as well as for its production value. Mineral mining, particularly

turquoise, dates back more than 1,000 years and includes prehistoric, colonial, and U.S.

Territorial mining. Pottery sherds found in the Cerrillos Hills date the use of mineral resources

from about 900 CE. Analysis of the sherds indicates that a large portion of them came from the

nearby San Marcos Pueblo, which between the middle 1300s and the middle 1400s was the

major center of pottery-making in the upper Middle Rio Grande Valley. Late in 1879, there was

a mining boom in the Cerrillos Hills with over 1,000 claims registered within a few years. The

metal mines eventually played out and turquoise was discovered in other areas of the southwest,

eventually decreasing mineral production in the Cerrillos Hills. The Cerrillos Hills State Park

offers miles of multi-use trails for visitors to reconnect with the area’s mining history.

Stop 2. Overturned Galisteo and Espinoso Formation on the east side of Laccolith (Bauer et

al., 1995) Overview of the local geology, laccolith emplacement models, and what we have

learned from AMS studies

Figure 3. Steeply tilted beds of the Galisteo Formation and the unconformably overlying Ancha

Formation,

To the northeast the lower part of the type section of the Galisteo Formation is exposed. Here,

the Galisteo Fm. dips steeply (30°-75°) to the SE and is locally vertical to slightly overturned.

Sub horizontal strata of the Pliocene-Pleistocene Ancha Formation overlie lower Galisteo strata,

creating an impressive angular unconformity. Views to the north and northwest illustrate the

deformation of Cretaceous and Eocene rocks that was caused by intrusion of magma associated

with emplacement of the Cerrllos Hills complex.

[Optional Stop 2a. Overturned beds of the Galisteo Fm. a.k.a. Garden of the Gods]

At this stop, you can lay hands on the geology of an overturned rock sequence and imagine a

time of the northern New Mexico bandits on the road to Santa Fe!

Figure 4. The Garden of the Gods along Highway 14 "Turquoise Trail"

The "Garden of the Gods" was long known to the locals as "ambush rock" because this is where

bandits hid and attacked prospectors and miners taking silver and gold from the Cerrillos mining

district to Santa Fe by wagon for assay. Here, spectacular exposures of vertical and near-vertical

Galisteo Fm. are exposed. Fossil fragmented bones of a brontotheres place the age of this section

as late Eocene. The near vertical dips of the Galisteo Fm. quickly diminish to 25°E on the

eastside of the road, which grade upward into the Espinaso Fm. that dips only 5°-10° E.

Stop 3. Devil's Throne (Bauer et al., 1995)

Lunch Stop

Figure 5. View to the west toward Devil's Throne along the Waldow Road.

Devil's Throne is an Oligocene hornblende-latite porphyry that was emplaced into the

Cretaceous Mancos Shale. At this stop we will have a short hike up a relatively steep canyon that

takes us through the floor of the laccolith. We end at the "throne" to investigate the metamorphic

contact between the intrusion and the Mancos Shale and observe beautiful igneous textures, such

as aligned hornblende phenocrysts.

Figure 6. Aligned hornblende crystals and xenoliths within the Devil's Throne hornblende-latite

porphyry

[Optional Stop 3a. Mary's Bar]

It's a bar, what else can we say.....

Figure 7. Mary's Bar.

Mary's Bar is located at the intersection of Main Street and First Street in the center of the

Village of Cerrillos. The Village of Cerrillos got its start in 1879 when silver, gold, copper, and

a few other metals were "rediscovered" in the adjacent Cerrillos Hills. Metal ores and turquoise

have been mined for centuries in the Cerrillos region by the Pueblo Indians and Spanish. The

rustic storefronts and dirt streets of the village have appeared in numerous feature films and TV

shows.

[Optional Stop 4. History of Coal Mining in Madrid]

Discussion the history of the coal mining and paleomagnetic work from intrusions and

volcanicastic rocks throughout the area

Figure 8. Madrid, New Mexico

Figure 9. View to the south towards the Ortiz Mounatins. Waste rock piles from Coal Mining

operations in the hills to the southeast of town of Madric.

Madrid is the oldest coal mining region in New Mexico. The town of Madrid was founded in the

1850s as a coal mining company town. By 1892, the yield from a narrow valley known as "Coal

Gulch" was large enough to warrant the construction of a 6.5 mile standard gauge railroad spur

connecting the area to the main line of Santa Fe Railroad. Coal mining continued until 1954,

after which Madrid became a ghost town. Water was, and still is, the limiting factor in any

further coal or ore mineral extraction in the region. Today, Madrid is a mecca for artists and

tourists as seen by the hillside sculptures and eclectic shops. The Mineshaft Tavern and the Coal

Mine Museum testify to the area’s mining history. The ending of the 2007 film Wild Hogs was

set and filmed in the town.

Paleomagnetic data from Tertiary intrusions and tilt-corrected volcaniclastic strata yields a grand

mean that is nearly indistinguishable from the 30 Ma reference direction (R=−6.6° ± 5.8°).

(Harlan and Geissman, 2009) Yet, paleomagnetic data from elsewhere in the basin suggest that

CCW rotations may be an important component of recent rift extension and deformation.

Figure 10. The Mine Shaft Tavern, Madrid, NM.

Stop 5. Crego Mine (Thompson et al., 2011)

Overview of Cerros del Rio volcanic field - AMS and Paleomagnetic data from La Cienega

volcano

The Cerros del Rio volcanic field is a middle Pliocene to Pleistocene basaltic volcanic field of

the axial Rio Grande Rift in central and northern New Mexico. It is a monogenetic volcanic field

that comprises about 60 cinder-spatter cones, occupies ~ 700 km2, and ranges in age from 2.7 Ma

to 1.1 Ma. Eruptive centers are typically central vent volcanoes, ranging from low-relief shields

to steep-sided, breached cinder and spatter cone remnants. They represent short eruptive events

that likely were derived from rapidly evolving reservoir-conduit systems. The Cerros del Rio

volcanic field abuts the Jemez Mountain volcanic field to the north, the San Felipe volcanic field

to the west, the Cienega volcanic field to the southeast, and the Cerrillos Hills Igneous Complex

to the south.

Figure 11. Map featuring the location and name of the major vents of the La Cienega complex,

west of the Santa Fe airport

Figure 12. Cinder quarrying at the La Cienega volcano

Cinder quarrying at the La Cienega volcano has exposed in near three-dimensions the magma

plumbing system of the volcano. Anisotropy of magnetic susceptibility and structural data show

sub-vertical and shallow magma flow both towards and away from the vent area. Paleomagnetic

data provide constraints on the relative emplacement sequence and sub volcanic deformation of

the magma feeder system. These data show that magma plumbing systems are more complicated

than common models predict and that the magma uses different pathways as it flows towards the

volcanic edifice.

Return to Santa Fe - Saint Johns College for the Ice Breaker - by 6 pm I think.....

References Cited

Bauer, P.W., Kues, B.S., Dunbar, N.W., Karlstrom, K.E., and Harrison, b., eds, 1995, New

Mexico Geological Society Fall Field Conference Guidebook – 46 Geology of the Santa Fe

Region, 338 pages.

Harlan, S.S., and Geissman, J.w., 2009, Paleomagnetism of Tertiary intrusive and volcaniclastic

rocks of the Cerrillos Hills and surrounding region, Española Basin, New Mexico, U.S.A.:

Assessment and implications of vertical-axis rotations associated with extension of the Rio

Grande rift, Lithosphere, v. 1, p. 155-173, doi:10.1130/L53.1

Maynard, S.R. 2000, Preliminary Geologic Map of the Golden Quadrangle, Santa Fe County,

New Mexico, New Mexico Bureau of Geology and Mineral Resources, Open-file Digital

Geologic Map OF-GM 36, Scale 1:24,000

Thompson, R.A., Sawyer, D.A., Hudson, M.R., Grauch, V.J.S., and McIntosh, W.C., 2011,

Cenozoic Volcanism of the La Bajada Constriction Area, New Mexico, USGS Professional

Paper 1720–C