Valles Caldera
Cerro la Jara, an approximately 246-foot (75 m) high forestedrhyolite lava dome within the caldera
Highest point
Elevation	11,253 ft (3,430 m)[1]
Coordinates	35°54′N106°32′W / 35.900°N 106.533°W /35.900; -106.533
Geography
Valles Caldera Location in New Mexico
Location	Sandoval County, New Mexico,US
Parent range	Jemez Mountains
Geology
Mountain type	ComplexCaldera
Volcanic zone	Jemez Lineament andRio Grande Rift
Last eruption	68,900 ± 1,000 yearsBP[2]
Climbing
Easiest route	New Mexico State Road 4
U.S. National Natural Landmark
Designated	1975

Valles Caldera National Preserve
Valles Caldera
Interactive map of Valles Caldera National Preserve
Location	Sandoval andRio Arriba counties,New Mexico,United States
Nearest city	Los Alamos, New Mexico
Coordinates	35°54′00″N106°31′59″W / 35.9°N 106.533°W /35.9; -106.533[3]
Area	89,766 acres (363.27 km2)
Established	July 25, 2000
Governing body	National Park Service
Website	Valles Caldera National Preserve

The Valles Caldera (orJemez Caldera) is a 13.7-mile-wide (22.0 km)volcaniccaldera in theJemez Mountains of northernNew Mexico.^[1]Hot springs, streams,fumaroles, natural gas seeps, andvolcanic domes dot the caldera landscape.^[4] The highest point in the caldera isRedondo Peak, an 11,254-foot (3,430 m)resurgent lava dome located entirely within the caldera and surrounded by moat-like flows of rhyolitic solidified lavas.^[5] Located within the caldera are severalgrass valleys, orvalles, the largest of which isValle Grande (locally/ˈvaɪ.eɪˈɡrɑːndeɪ/VY-ayGRAHN-day), the only one accessible by a paved road. In 1975, Valles Caldera was designated as a National Natural Landmark by the National Park Service with much of the caldera being within theValles Caldera National Preserve, a unit of theNational Park System.^[6] The area has a varied history involving cultural significance, economic resources, scientific studies, and complex geological setting.

Use of Valles Caldera dates back to prehistoric times: spear points dating to 11,000 years ago have been discovered.^[7] SeveralNative American tribes frequented the caldera for hunting prolific game and gatheringobsidian that is common in this area. The obsidian wasknapped into tools and weapons while wild game was followed and hunted seasonally. Obsidian from the caldera was traded by tribes across much of the Southwest. Eventually, the Spanish, and later Mexican settlers along with theNavajo and other tribes came to the caldera seasonally for grazing livestock. This often resulted in periodic clashes and raids between tribes and cultures. Later, as the United States acquired New Mexico as part of theTreaty of Guadalupe Hidalgo in 1848, the caldera became the backdrop for the Indian wars with theU.S. Army. Around the same time, the caldera and its forests began to be used commercially for ranching and logging.^{[citation needed]}

The caldera became part of theBaca Ranch in 1876. TheBacas were a wealthy family given the land as compensation for the termination of a grant given to their family nearLas Vegas, in northeastern New Mexico. The family was given four other parcels by the US Government as well, another one in New Mexico, one in Colorado, and two in Arizona. This area, 100,000 acres (40,000 ha), was calledBaca Location Number One orBaca Float Number One. Since then, the land has been through a string of exchanges between private owners and business enterprises. It was owned by Frank Bond in the 1930s. Bond, a businessman based in nearbyEspañola, ran up to 30,000 sheep in the caldera, significantly overgrazing the land and causing damage from which the watersheds of the landscape are still recovering.^{[citation needed]}

The land was purchased by the Dunigan family from Abilene, Texas in 1963. Pat Dunigan did not obtain the timber rights and the New Mexico Lumber Company logged the property heavily - removing significant amounts of old-growthdouglas fir andponderosa pine. Dunigan bought out the timber rights in the 1970s and slowed the logging. He negotiated unsuccessfully with theNational Park Service and theUS Forest Service for possible sale of the property in the 1980s.^[7]

The Valles Caldera Preservation Act of 2000 signed byPresident Clinton on July 25, 2000, created the Valles Caldera National Preserve (VCNP).^[8] The legislation provided for the federal purchase of this historical ranch with funds coming from theLand and Water Conservation Fund derived from royalties the US government receives from offshorepetroleum andnatural gasdrilling.^[4] The Dunigan family sold the entire surfaceestate of 95,000 acres (380 km²) and seven-eighths of thegeothermalmineral estate to thefederal government for $101 million. As some sites of the Baca Ranch are sacred and of cultural significance to theNative Americans, 5,000 acres (20 km²) of the purchase were given to theSanta Clara Pueblo, which borders the property to the northeast. These include the headwaters of Santa Clara Creek, which is sacred to the pueblo.^[4][7] On the southwest corner of the land, 300 acres (1.2 km²) were to be ceded toBandelier National Monument.^{[citation needed]}

The Baca Ranch, also known as Baca Location No. 1, had possessed a mixed range oftree species and significantbiodiversity. At the time of the purchase, the ranch was home to 40 miles (64 km) of pristinetrout streams, 66,118 acres (26,757 ha) ofconifer forest, 17 endangered plant and animal species, and 25,000 acres (10,000 ha) ofgrassland grazed by 8,000elk, New Mexico's largest herd. The preserve is encircled by federal lands, including theSanta Fe National Forest, theJemez National Recreation Area, andBandelier National Monument.^[9]

The Valles Caldera Preservation Act of 2000 also created the Valles Caldera Trust, an experimental management organization consisting of nine board members, including seven appointed by thePresident of the United States.^[10] The Trust combined private-sector practices with federal land management protocol. Under the terms of the Valles Caldera Preservation Act, the preserve was to become financially self-sustaining by 2015.

Environmentalists lobbied for the more inclusive protections of national park status instead of the Trust model, but then-SenatorPete Domenici (R) insisted on the experimental approach as a condition for his support for public purchase. Beginning in 2010, US SenatorJeff Bingaman (D) introduced legislation that would transfer the property to theNational Park Service as anational preserve.^[11] The 2011 bill^[12] was supported by the VCNP trustees and a majority of New Mexico's Congressional delegation. On December 19, 2014, PresidentBarack Obama signed the2015 National Defense Authorization Act, which transferred administrative jurisdiction of the preserve from the Valles Caldera Trust to the National Park Service.^[13] After a brief transition period, the National Park Service assumed day-to-day management on October 1, 2015. On October 10, the preserve held an official dedication with dignitaries including U.S. Secretary of the InteriorSally Jewell, U.S. SenatorTom Udall, U.S. SenatorMartin Heinrich, former U.S. SenatorJeff Bingaman, National Park Service Intermountain Region Director Sue Masica, and the first National Park Service Superintendent of Valles Caldera National Preserve, Jorge Silva-Bañuelos.^[14]

In July 2011, theLas Conchas Fire, started by a power line on nearby private land, burned 30,000 acres (120 km²) of the Valles Caldera National Preserve. Thewildfire burned a total of 156,000 acres (630 km²) in theJemez Mountains, including most of neighboringBandelier National Monument.^[15] The Jemez Mountains and surrounding areas of the southwest incorporate dry climates, grasslands, and certain tree species (likePinon) that evolved to exist with wildfires. Changes in climate andanthropogenic interference with the fire cycle and habitats, has led to fires that are hotter and more intense. These types of fires are more difficult for ecosystems to recover from.^{[citation needed]}

The circulartopographic rim of the caldera measures 13.7 miles (22.0 km) in diameter.^[1] The caldera and surrounding volcanic structures are one of the most thoroughly studiedcaldera complexes in the United States. Research studies have focused on the fundamental processes ofmagmatism,hydrothermal systems,ore deposition, and glassy rhyolites.^[16] Nearly 40 deep cores have been examined, resulting in extensive subsurface data and geothermal information.^{[citation needed]}

Valles Caldera is the younger of two calderas known at this location, having collapsed over and buried the olderToledo Caldera, which in turn may have collapsed over yet older calderas. The associated Cerros del Riovolcanic field, which forms the easternPajarito Plateau and theCaja del Rio, is older than the Toledo Caldera. The Toledo and Valles Calderas formed during eruptions 1.61 million and 1.25 million years ago, respectively.^[17][18] The caldera-forming Toledo eruption emplaced the Otowi member of theBandelier Tuff 1.61 million years ago, which can be seen alongcanyon walls west of Valles Caldera, includingSan Diego Canyon. The younger Tshirege Member of the Bandelier Tuff was formed during the Valles Caldera eruption 1.23 million years ago.^[2] The now eroded and exposed orange-tan, light-colored Bandelier Tuff from these events creates the stunningmesas of thePajarito Plateau.

Caldera is the type locality for aresurgent dome caldera, the formation of which was first developed by C.S. Ross, R.L. Smith, and R.A. Bailey during field work at Valles in the 1960s.^[19] This type locality and associated studies have been used to studied other resurgent domes around the world, includingYellowstone Caldera. After the initial caldera-forming eruption at Valles, the Redondo Peak resurgent dome was uplifted beginning around 1.2 million years ago.^[2] Minor eruptions of moatrhyolitic flows occurred from approximately 1.16 million years ago at Cerro del Medio to 0.07 million years ago at Banco Bonito, along a structural ring fracture zone.^[20][21][22] The El CajetePumice and Battleship RockIgnimbrite were emplaced in a single eruptive event 74,200 ± 1,100 years ago, followed by the eruption of the Banco Bonitoobsidian flow during the youngest eruption of Valles Caldera, at 68,900 ± 1,000 years ago.^[2] The caldera and surrounding area continue to be shaped by ongoing volcanic activity. Seismic investigations show that a low-velocity zone lies beneath the caldera, suggesting the presence of partial melt within a remainingmagma chamber at between 5 and 15 km depth.^[23] An active geothermal system withhot springs andfumaroles exists today.^[1] These calderas and associated volcanic structures lie within theJemez Volcanic Field. This volcanic field lies at the intersection of theRio Grande Rift, which runs north–south through New Mexico, and theJemez Lineament, which extends from southeasternArizona northeast to westernOklahoma. The volcanic activity here is related to the tectonic movements of this intersection.^[24]

NASA used the caldera in October to November 1964 and again in September 1966 to geologically train theApollo Astronauts in recognizing volcanic features, such as ash flow tuffs, pumice air falls, and rhyolite domes. Notable geologist instructors included Roy Bailey.^[25]

Panoramic view of the Valles Caldera, from the south east rim; in the distanceRedondo Peak (aresurgent dome) and therhyolitelava dome of Cerro la Jara are visible on the far left.

According to theKöppen climate classification, Valles Caldera has asubarctic climate (Dfc), with cold winters and mild summers. The caldera is subject to strong temperature inversions, causing very cold nights year round and high diurnal temperature variation.

The volcanic properties of Valles Caldera make it a likely source for renewablegeothermal energy. Some people oppose the development of geothermal energy, considering it destructive to the scenic beauty, recreational and grazing use. Its impact on thehot springs and supplying aquifers is unknown as experiences from other past geothermal projects proved that production of reservoir fluids had dramatic impacts to the surface thermal features.^[30]

Valles Caldera was home to the first experiments into development of anEnhanced geothermal system (EGS) orHot-dry-rock (HDR) geothermal system, beginning in 1974 by theLos Alamos National Laboratory at theFenton Hill reservoir, approximately 3 km west of Valles Caldera. Originally, the Fenton Hill site was chosen as an EGS laboratory in hopes that the proximity to Valles Caldera would increase the temperature of the bedrock, thus requiring shallower drill depths. The abundance ofhydrothermal fluids discharged from the nearby caldera resulted in hydrothermal alteration of the rocks at depth, weakening the sealed nature of the reservoir.^[31] The Fenton Hill HDR experiment was finally abandoned in 1998.^[32] The experiments demonstrated that a potential EGS reservoir must be characterized by lowpermeability, crystalline basement rock with no activefaults or joints.^[31]

From 1959 to 1983, approximately 40 exploratory geothermal wells were drilled into the Redondo Creek Graben as part of the Baca geothermal field, a joint operation by the United StatesDepartment of Energy and the Union Oil Company of California.^[33] Despite measuring a maximum temperature of 342 °C and having a likely production capacity of 20 MWe, the geothermal field was too small to be economic.^[32][34] Three scientific cores were drilled in Valles Caldera during the mid-1980s as part of the United States Continental Scientific Drilling Program in order to analyze the chemistry of geothermal fluids and the presence of a vapor-dominated cap in the Sulphur Springs region. The maximum bottom hole temperature measured during drilling was 295 °C.^[35] Overall, the geothermal reservoir at Valles Caldera is liquid-dominated rather than vapor-dominated and has a neutral-chloride fluid chemistry with a maximum temperature below 300 °C.^[32]

A number of recreational and/or historical uses take place in Valles Caldera. Many of these uses involve trails. Over two dozen official hiking and biking trails of varying length are available. Maps and trail descriptions may be found in "Hiking Trails in Valles Caldera National Preserve," by Coco Rae. Valles Caldera has many miles of ranch roads, livestock and game trails. These include a network of trails currently designated for horse riding.^[36][37] Historically, Valles Caldera was a location forequestrian endurance races. After establishment of VCNP, the first race in the caldera was held in 2009. The largest grass valley, Valle Grande, is a venue forski orienteering. Activities are open to the public, though some require reservations. Customer service and concierge services are provided by thePublic Lands Interpretive Association. The valley floor is above 8,000 ft (2,400 m) altitude.^[38]

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Throughout the caldera, the grass valleys appear groomed: there are few saplings and mature trees lack lower branches. This is due to heavybrowsing byelk andcattle and because of frequent grass fires of human and natural origin which kill the lower branches on theEngelmann spruce,Douglas-fir andPonderosa pine that populate the uplands around the lower-elevationMontane grasslands dominating the bottoms of the calderas. The grasslands were native perennialbunch grass maintained by frequent fire before sheep and cattle grazing. Although the grass appears abundant, it is a limited resource and its growing season is short. Through the VCNP's limited grazing program, it feeds hundreds of cattle in the summer and thousands more of elk in the warm seasons, in drought winters, and during most of the year. The nutritional value of the bunch grasses is considered low or poor quality. Other wildlife that inhabits the area areGolden Eagles, stripedBadgers, and the GunnisonPrairie Dog, to name a few.^[39] The National Park Service states that elk population in Valles Caldera is the second largest herd in New Mexico. Hunting is permitted within the National Preserve under certain restrictions and times of the year.^[40][41]

Valles Caldera has provided severalfilming locations,^[42] most for films in theWestern genre. Some of these locations include exterior sets, such as the weathered "ranch house" that can be seen from the highway in Valle Grande, and a small "town".

• 1971Shoot Out
• 1977Peter Lundy and the Medicine Hat Stallion (TV)
• 1982The Gambler (TV)
• 1994Troublemakers
• 1995Buffalo Girls (TV)
• 1997Last Stand at Saber River (TV)
• 2003The Missing
• 2007Seraphim Falls^[43]
• 2010Kites (film) (Hindi/Indian Film)
• 2013The Lone Ranger
• 2012–2017Longmire (TV series)^[44]

• Jemez Pueblo, New Mexico
• Valle Vidal

• Fraser Goff,Valles Caldera: A Geologic History. 2009, University of New Mexico Press.ISBN 978-0-8263-4590-5.ReviewArchived April 7, 2012, at theWayback Machine atNew Mexico Magazine: "No matter your interest in the Valles Caldera, you'll learn something new in Fraser Goff's new book."
• Coco Rae,"Hiking Trails in Valles Caldera National Preserve". 2020. The complete trail guide to VCNP.

Wikimedia Commons has media related toValles Caldera.

• Valles Caldera National Preserve, official website
• The Physics Institute of Brazil's Valles Caldera website (English)
• Geologic travel guide fromAmerican Geological Institute
• Caldera Action, advocacy organization
• Valles Caldera National Preserve travel guide from Wikivoyage

• VEI-7 volcanoes
• Rift volcanoes
• Jemez Mountains
• Volcanoes of New Mexico
• Calderas of New Mexico
• Complex volcanoes
• Pleistocene calderas
• National Natural Landmarks in New Mexico
• Santa Fe National Forest
• Landforms of Rio Arriba County, New Mexico
• Landforms of Sandoval County, New Mexico
• Quaternary New Mexico

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