The story of the geology of the Cerrillos Hills is the story of magma from
deep within the earth 34 million years ago pushing its way upward and
intruding into the older geology in this area. In the Cerrillos area, this
intrusive material forced its way into the Mancos Shale and the Galisteo Formation,
disrupting them, baking them, injecting them with mineral-rich fluids, and then
erupting out at the surface to form a volcano. It is this process of intruding
and pushing upward on older formations like the Galisteo Formation that created
the spectacle of upturned geology that is the Garden of the Gods. It also this
process of intrusion and eruption that created the Cerrillos
Hills.
The disturbed sedimentary Galisteo Formation, exposed
around mile markers 33-35 of Hwy 14, is known locally as "the Little Garden of
the Gods" -- with a tip of the stratum to the "real" Garden of the Gods, which is
outside Colorado Springs, Colorado. The older geology (starting 60 millionh years
ago) is nearer Cerrillos, the yellow Diamond Tail Formation. The newer red-white-yellow
Galisteo Formation (to 30 million years ago) terminates in a petrified-wood-rich
zone lying to the east of Hwy 14. Ambush Rock is a sandstone slab which has been
pushed to vertical, and whose northern extension (east of the roadway) is
actually tilted beyond 90 degrees.
As a result of isotopic analysis of lead samples -- the relative
proportions of the various isotopes of lead -- we now know that
the Cerrillos deposits of galena were formed by mineralizing
fluids associated with two distinct stocks (magma intrusions) and
their associated faulting, creating a complicated swarm of
cross-cutting ore-bearing veins. This would suggest that a minimum of
two distinct volcanic events contributed to the building of the
Cerrillos Hills.
Thirty-four to 30 million years ago the original Cerrillos Hills
were formed as described, but over these last 30 million years
the cumulative effects of weather and gravity have left only the
erosional remnants of those ancient Tertiary volcanos. In the
words of geologist Scott Renbarger, when we look at the Cerrillos
Hills today we see the 'frozen plumbing of an ancient
volcanic complex'. The missing volcano material has been in
its turn deposited in low-lying areas -- the local Tertiary-age
deposition known as the Espinaso
Formation. (Geology seems to be mostly the story of
building up mountains and then eroding them away!)
The Ortiz Mountain complex to the south of the Cerrillos Hills
was in its volcanic glory about 29 million years ago.
Around 20 million years ago this era of volcanism came to a close
in New Mexico with a regional episode of crustal extension. The
state was split by a great series of north-south offset
depressions called the Rio Grande Rift. The
crust adjacent to these depressions buoyed upward into
steep-faced mountains such as Sandia, and differential offset
created escarpments like La Bajada. The Rio Grande, following the
growing depressions, came into existence at this time. The basins
were filled with thick deposits of erosional material washed down
from the flanking uplifts, the gravelly fill now known as the
Santa Fe Formation, the host of the most popular aquifer where
New Mexicans mine their water. In some areas at this time thick
flows of dark basalt were also laid down.
There are in the Cerrillos Hills a few thin surficial stream
deposits and pediment gravels called Quaternary Alluvium that
date from about 2 million years ago, most notably represented by
the gravelly Ancha Formation that covers the plain north and east
of the hills.
The Tertiary Cerrillos volcanos created concentrations of
different minerals throughout the hills that have attracted
people from near and far. There is an extensive history of mining
in the Cerrillos area, from the earliest prehistoric
Indian turquoise mining prior to
1000 A.D., to Spanish mines of the 17th century such as the Mino del Tiro,
and to American mining of the 19th and 20th centuries.
This is one of the oldest mining areas in North America. There is
evidence of pre-Columbian vein workings and later smelter sites
which are of immense historical and archaeological value and
indicate sources of metallic and other substances used by past
cultures. Except for turquoise (and sometimes including it),
mining in the area has often been marginal and aimed at
recovering localized concentrations of sulfides of zinc, lead,
iron, and silver, deposits of copper ores, and, though dreams
would have it otherwise, never much more than a trace of
gold.
All abandoned mines are being surveyed for fencing or other
closures (appropriate grating will be placed at known bat
habitats.)
The nature of the mining to date has been mostly benign with
respect to toxic substances, but there are two mill-site
locations within the boundaries of the 19th century Cerrillos
Mining District that are under the current scrutiny of the
Environmental Protection Agency (concerns are for lead, cadmium,
and arsenic.) Both of these EPA locations lie outside of the
park.
The Cerrillos Mining District, of which the Cerrillos Hills
Historic Park occupies a small part, was placed on the New Mexico
Register of Cultural Properties in 1973.
Ecology
The Cerrillos Hills are representative of the
piñon-juniper ecosystem, roughly from 4500' to 6500' [1400-2000 m.] in
elevation. The widely spaced, mixed stands of piñon and juniper give this
belt or life zone a distinctive individuality entirely different from that of any
other place. It is often referred to as the Pygmy Forest.
Grassland is the dominant vegetative type along with piñon,
juniper, and occasional mountain mahogany. In the arroyo bottoms
a shrub community of rabbit bush (chamisa), Gambel oak, wavyleaf
oak, New Mexico olive, Apache plume, four-wing saltbush, wafer
ash, and introduced Russian olive and salt cedar occur. See the
Catalog of Nature in the Park for
a more comprehensive and descriptive list of all the plants and
animals.
Cacti are represented by prickly pear, candelabra cholla and
dagger cholla, and the green-flowered torch cactus. Our yuccas
are the Banana yucca, the Narrowleaf yucca, and the Soaptree
yucca.
Several significant permanent springs occur in the Cerrillos
Hills which are focal points for a wealth of diverse plants and
animals including some small valley cottonwoods and willows. As
nearly all of these springs have been degraded by current grazing
and land use practices, protection and restoration of riparian
areas will be critical to maintaining the ecological integrity of
the area.
The area supports a diverse population of wildlife. Vertebrate
animals inhabiting the Cerrillos Hills are those one might expect
in hilly grassland and woodland in central New Mexico: At least
twenty-five species of wild mammals (including bobcats,
porcupine, coyote and mule deer), four species of bats, numerous
rodents, reptiles and amphibians, as well as innumerable
invertebrates. More than thirty species of birds have been
identified including great horned owls and golden eagles.
While the systematic inventory of the area is not yet complete,
it is likely that the abandoned mines and natural habitats of the
Cerrillos Hills are home to avian species and bats. For bats, ten
species of concern that are tracked by the
Natural Heritage New Mexico Program
are know to occur in Santa Fe County and all have the potential to exist in this
area. In general, bat populations are declining because they are highly sensitive to
habitat disturbances. Protection of the hills would provide an
important refuge for their future protection and study. In a
natural area this large, it is also possible that a systematic
biological survey would reveal additional rare, threatened or
endangered species.
A park that will manage and preserve county, Bureau of Land Management, and State
Trust Lands under a partnership arrangement will connect critical
resources and habitats and protect riparian areas and springs for
wildlife access. This four thousand acre undeveloped area will
also provide some relief for the county recharge/watershed
resources, which will in turn sustain populations of both people
and wildlife, and we are preserving the viewshed of the Turquoise
Trail National Scenic Byway, with its scenic vistas and unique
geological features such as the colorful sandstone Galisteo
Formation out-croppings in the Garden of the Gods.
The Cerrillos Hills Park Coalition - in
conjunction with Jan-Willem Jansens and
Common Ground - has
begun in the Fall of 2000 a five-
year trial spring restoration project. Our test spring is
presently nothing more than a seep at the bottom of the arroyo in
the center of the the photo to the left, though before the
surrounding land was grazed barren it probably hosted a more
healthy and diverse biota. The suggestion was, "Pick one of
the worst ones and let's see what we can do with it." So
we did.
Overview Of Arroyo
November 5th, 2000, was baseline data
accumulation day. A crew of volunteers quantified and recorded the
characteristics of the microenvironment of the spring, such as salient geology,
degree of groundcover, and the variety of species. With this baseline information
we expect to produce in the coming months meaningful comparative analyses.
This website is maintained by the Cerrillos
Hills Park Coalition
and is dedicated to the creation, enhancement and stewardship
of an historical, recreational, and cultural open space in
the
Cerrillos Hills, Santa Fe County, New Mexico, USA
