Contracted to the NM BUREAU OF MINES AND MINERAL RESOURCES for
QUADRANGLE-SCALE GEOLOGIC MAPPING
LANDSCAPE AND TOPOGRAPHY
The Cerrillos Hills is a group of low mountains that covers
an area about 18 square miles [46.6 square kilometers] north of the village of
Cerrillos, in Santa Fe County, New Mexico. The Cerrillos Hills' lowest elevation
is 5600 ft [1,706.9 meters], along the Galisteo Creek. Most of the Cerrillos Hills
is hilly terrain cut by locally steep-sided gulches and arroyos. The hilltops of
most of the land range from 6000 to 6200 feet [1,828.8 to 1,889.8 meters] above
sea level. Several prominent hills (Cerro Cosena, Grand Central Mountain, Cerro
Bonanza, Lucera Hill, and Achavica Mountain) rise to summits over 6900 ft
[2,103.1 meters]. The Santa Fe plateau, on the on the north side of the Cerrillos
Hills, lies at about 6300 ft [1,920.2 meters] above sea level.
Galisteo Creek borders the southern flank of the Cerrillos Hills and flows east
to west, to the Rio Grande. San Marcos Arroyo cuts through the southeastern part
of the Cerrillos Hills and joins Galisteo Creek at the village of Cerrillos. Both
streams flow intermittently, though Galisteo Creek usually has at least a trickle
of water. Both streams are capable of flash floods as well. Other gulches and
arroyos draining the Cerrillos Hills are ephemeral.
The Cerrillos Hills are covered by the Madrid, Picture Rock, Tetilla Peak, and
Turquoise Hill U.S. Geological
Survey 7.5-minute topographic maps.
The Precambrian Era is the first part of Earth's history,
beginning with the formation of the Earth, about 4,500 million years ago and
ending with the advent of complex life forms 570 million years ago. In north-central
New Mexico the Precambrian Era is represented by 1,600- to 1,700-million years-old
metamorphic rocks and 1,400-million years-old granite in the Sandia and Sangre de
Cristo Mountains. Precambrian rocks are not exposed in the Cerrillos Hills, except
as isolated boulders of granite found as inclusions in the igneous rocks. These
inclusions were likely carried up several thousand feet by the molten rock to their
There is no record of the Earth's history in New Mexico from about 1400 million
years ago to the Mississippian Period, about 330 million years ago. Geologists
surmise that at least for the latter part of that time, the land surface was above
sea level and was probably fairly level.
The Paleozoic Era began 570 million years ago. As mentioned
before, there is no record of the early part of the Paleozoic Era in the Cerrillos
Hills area. During the Mississippian and Pennsylvanian Periods, 330 to 280 million
years ago, north-central New Mexico lay under a shallow sea. The limestone that
caps the Sandia Mountains and is found in the upper Pecos region of the Sangre
de Cristo Mountains was deposited during the Pennsylvanian Period.
During the Permian Period, at the end of the Paleozoic Era, and the Triassic
Period, at the beginning of the Mesozoic Era, 280 to 195 million years ago, the
seas receded from north-central New Mexico. Sandstone and mudstone was deposited
on broad flood plains. The earliest reptiles arose during the Permian Period and
dinosaurs appeared during the Triassic Period. Permian and Triassic rocks of the
region are typically reddish to maroon and crop out over a broad area of New Mexico.
The region stayed above sea level during the Jurassic Period and the early
Cretaceous Period (195 to 100 million years ago). Sand and mud, partly eroded from
volcanoes in southwestern Arizona, California, and Nevada, were deposited on river
flood plains during the Jurassic Period, as well as limestone and gypsum in a
shallow lake hundreds of miles wide. Morrison Formation sediments of the late
Jurassic Period are the oldest sedimentary rocks that crop out in the Cerrillos Hills.
There was no further deposition of sediments from the end of the Jurassic Period,
140 million years ago, until the beginning of the late Cretaceous Period, 100
million years ago. The land continued to be above sea level during this time.
The sea returned to north-central New Mexico in the late Cretaceous Period.
Sandstone and shale of the Dakota Formation, and black to gray shale, and lesser
sandstone and limestone of the 3,000-foot [914.4 meters] thick Mancos Shale, were
deposited in a shallow sea. This shallow sea extended from the Gulf of Mexico to
the Arctic Ocean and covered most of the Rocky Mountain and High Plains states
and provinces. Sandstone of the Dakota Formation, often displaying its characteristic
fossil worm burrows and traces, crops out in several locations around the Cerrillos Hills.
The black or gray shale of the Mancos Shale is widely exposed in the Cerrillos
Hills. The Mancos Shale forms most of the lowlands along County Road 52 (the
Waldo Road) west of Cerrillos village. Ammonite fossils are often found in the
The sea retreated again from the Cerrillos Hills area in the late Cretaceous Period
and was replaced by an environment of sluggish streams and swamps separated from
the sea by a broad sandy beach. The sandstones and shales deposited during that
time are known as the Mesa Verde Group, which extends over much of the Four Corners
region. The large coal deposits of the Colorado Plateau, and the smaller ones of
the Madrid area, occur in Mesa Verde Group rocks. The Mesa Verde Group, with a
handful of small coal prospects, crops out in the southeastern part of the
During the latest part of the Cretaceous Period and the beginning of the Tertiary
Period of the Cenozoic Era, western North America experienced a mountain-building
episode known as the Laramide Orogeny. (orogeny = mountain-building). The modern
Rocky Mountains developed during this time. The entire area was eroded, though the
Cerrillos Hills area was not tilted.
The end of the Cretaceous Period and the beginning of the Tertiary Period, about
65 million years ago, is marked by the disappearance of the dinosaurs and many
other species, and the emergence of mammals and flowering plants. It is believed
by many geologists that this extinction was caused by a catastrophic event,
probably by the collision of a large meteorite with the earth. Evidence for this
event cannot be found in the Cerrillos Hills area.
During the earliest part of the Tertiary (65 million to about
35 million years ago) a broad intermontane basin extending from Lamy to Placitas
filled with sedimentary material derived from nearby mountains. These sedimentary
rocks are sandstone and mudstone of the Diamond Tail and Galisteo Formations.
Sandstone of the Diamond Tail Formation forms the buff-colored cliffs along NM-14
between Madrid and Cerrillos. The Diamond Tail and Galisteo Formations are
beautifully exposed on the eastern side of the Cerrillos Hills, where they have
been tilted to vertical. The vivid red mudstone between the sandstone layers belong
to the Galisteo Formation.
The Cerrillos Hills began to take their present form with the invasion of the
sedimentary rocks by molten rock (magma) 34 to 30 million years ago. The formation
of the Cerrillos Hills Igneous Complex resulted in four important features. The
first is that magma replaced much of the sedimentary rocks. Second, the remaining
sediments were pushed up around the edges of the intrusive complex. Third, the
deposits of silver, lead, zinc, and copper formed as the last stage of the
crystallization of the igneous rocks. Fourth, volcanic rocks, in the form of lavas
and pyroclastic flows, were erupted from a source thought to lie on the northeastern
side of the Cerrillos Hills. The volcanic rocks that erupted from the Cerrillos
Hills and the Ortiz Mountains make up the Espinaso Formation. The Espinaso Formation
is exposed in the northeastern part of the Cerrillos Hills and makes up the low
hills to the east of NM-14, north of Galisteo Creek.
The Cerrillos Hills Igneous Complex is considered by
geologists to be part of the Ortiz Porphyry Belt, a 25-mile [40.2 kilometer]
long, north-south trending group of igneous rocks that begins at South Mountain
in the south, and ends at La Ciénega in the north. Throughout the Ortiz Porphyry
Belt, the igneous rocks have invaded sedimentary rocks ranging from the Mississippian
Period to the Tertiary Period. In the San Pedro Mountains, the Ortiz Mountains,
and in the Cerrillos Hills, the igneous rocks have a direct relationship to the
ore deposits found there.
In the Cerrillos Hills, igneous rocks are both plutonic (or intrusive) and volcanic
(extrusive). The intrusive rocks can be divided into two main groups. The first
group is about 34 million years old and is composed of quartz-bearing andesite-
latite porphyry. The andesite-latite porphyry generally invaded the sedimentary
rocks in sheets parallel to the sedimentary rocks' layering. The individual sheets
are called sills. The sills were probably fed by vertical fractures. These vertical
fractures filled with igneous rock are called dikes. A series of stacked sills
connected by dikes is called a Christmas-tree laccolith. It is believed that such
a laccolithic structure existed in the Cerrillos Hills, though its original form
has been mostly destroyed by younger plutonic rocks, and later tilting and erosion.
Around 30 million years ago a series of quartz-poor latite and monzonite bodies
(dikes and stocks) intruded the Cerrillos laccolith. These intrusions pushed the
country rock up and tilted it away from the centers of the intrusive bodies. The
monzonite stocks that form the highest hills in the Cerrillos Hills were formed
at this time. A small, as yet unmined, copper deposit formed in the central part
of the Cerrillos Hills at this time. Veins containing lead, zinc, and silver formed
in northeast-trending fractures shortly afterwards (within a million years or
From about 30 million years to about 3 million years ago, a
series of linked basins formed (the Rio Grande Rift) and filled with sediment.
The Cerrillos Hills area was eroded and the broad plain of the Santa Fe Plateau
formed. Geologists call this feature a peneplain. The peneplain appears to have
extended over the Cerrillos Hills, with the highest hills, e.g.
Cerro Cosena, Grand Central Mountain, Cerro Bonanza, Lucera Hill, and Achavica
Mountain, left standing above its sloping surface. Similar peneplains are found
over much of New Mexico. One of the most striking is the Ortiz Surface, which
flanks the Ortiz Mountains on all sides and is easily viewed from the Cerrillos Hills.
During the period 2.8 million to 1.5 million years ago, during the time periods
known as the Pliocene and Pleistocene Epochs, streams draining the Sangre de Cristo
Mountains deposited sand and gravel on the Santa Fe Plateau. This deposit is known
as the Ancha Formation. The Ancha Formation covers the Plateau with up to 40 ft.
of sand and gravel. It can be seen in the eastern and northern parts of the
Cerrillos Hills. Wolf Road, in the eastern part of the Cerrillos Hills, runs along
a ridge capped with Ancha Formation gravel. A similar deposit called the Tuerto
Gravel caps the Ortiz Surface that flanks the Ortiz Mountains.
As the Rio Grande Valley deepened in the last 1.5 million years, so did Galisteo
Creek. Tributary arroyos and gulches cut down through the rock as well, first
stripping away the Ancha Formation and Tuerto Gravel deposits, leaving them perched
on mesa tops. Both Galisteo Creek and San Marcos Arroyo have significant terrace
deposits that record times in recent geologic history when the streams were tens
of feet higher than they are now and left stream-worn gravel on benches above their
Akright, R.L., 1979, Geology and mineralogy of the Cerrillos
copper deposit, Santa Fe County, New Mexico: New Mexico Geological Society,
Guidebook 30, pp. 257-260.
Amindyas, C.A., and Brookins, D.G., 1988, Geochemical study of
hydrothermally altered rocks, Cerrillos porphyry copper deposit, Santa Fe County,
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Bachman, G.O., 1975, Geologic map of the Madrid Quadrangle,
Santa Fe and Sandoval Counties, New Mexico: U.S. Geological survey Geologic
Quadrangle Map GQ-1268, scale 1:62,500.
Bauer, P., and Giles, D.L., 1995, Turquoise: minipaper
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Smith, E.W., and Kottlowski, F.E., Third-day road log, from Santa Fe to the
Cerrillos Hills, Cerrillos and the Ortiz Mountains: New Mexico Geological Society
Guidebook, 46th Field Conference, Geology of the Santa Fe Region, pp 60-61.
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Elston, W.E., 1967, Summary of the mineral resource of
Bernalillo, Sandoval, and Santa Fe Counties, New Mexico: New Mexico Bureau
of Mines and Mineral Resources, Bulletin 81, 81 pp.
Disbrow, A.E., and Stoll, W.C., 1957, Geology of the Cerrillos
area, Santa Fe County, New Mexico: New Mexico Bureau of Mines and Mineral
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Lee, W.T., 1913, The Cerrillos coal field, Santa Fe County,
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Preliminary geologic map of the Picture Rock 7.5-minute quadrangle: New
Mexico Bureau of Mines and Mineral Resources, Open-File Report, OM- .
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biostratigraphy of Eocene Galisteo Formation, north-central New Mexico:
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geologic map of the Madrid 7.5-minute quadrangle: New Mexico Bureau of Mines
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Milford, H.E., 1994, History of the Los Cerrillos mining
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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
Cerrillos Hills, Santa Fe County, New Mexico, USA