Chaco Culture National Historical Park is a United States National Historical Park in the American Southwest. It has many ruins of ancient homes built by the Ancestral Puebloans. The park is in northwestern New Mexico, between Albuquerque and Farmington, in a remote canyon shaped by the Chaco Wash. It contains the largest collection of ancient ruins in the United States north of Mexico. These ruins preserve one of the most important cultural and historical areas in the country.

From AD 900 to 1150, Chaco Canyon was a major center for the Ancestral Puebloans. They cut sandstone blocks and transported wood from far away to build fifteen large structures. These buildings were the largest in North America until the 19th century. Studies of the stars and celestial events at Chaco suggest that some structures, like the "Sun Dagger" petroglyph on Fajada Butte, may have been aligned with the sun and moon. This required many years of careful observation and construction. A long drought beginning in 1130 is believed to have caused the people to leave the area, leading to the canyon’s eventual abandonment.

A UNESCO World Heritage Site, the park is in the dry, sparsely populated Four Corners region. The ruins are fragile, and erosion from tourists has caused Fajada Butte to close to the public. The Hopi and Pueblo people consider these sites sacred ancestral lands. They share stories passed down through generations about their historical connection to Chaco. While park preservation efforts sometimes conflict with Native beliefs, tribal leaders work with the National Park Service to share knowledge and honor the Chacoan culture.

The park is located along the Trails of the Ancients Byway, a designated scenic route in New Mexico.

Geography

Chaco Canyon is located within the San Juan Basin, on top of the large Colorado Plateau. It is surrounded by the Chuska Mountains to the west, the San Juan Mountains to the north, and the San Pedro Mountains to the east. Ancient Chacoans used dense forests of oak, piñon, ponderosa pine, and juniper to get timber and other resources. The canyon lies in lowlands that are surrounded by dune fields, ridges, and mountains. It is aligned roughly from northwest to southeast and is bordered by flat, high landforms called mesas. Large gaps between the southwestern cliff faces—side canyons called rincons—helped funnel rain-bearing storms into the canyon, increasing local rainfall. The main Chacoan structures, such as Pueblo Bonito, Nuevo Alto, and Kin Kletso, are at elevations of 6,200 to 6,440 feet (1,890 to 1,960 meters).

The canyon floor slopes gently downward to the northwest at a rate of 30 feet per mile (6 meters per kilometer). It is divided by the Chaco Wash, an arroyo that rarely holds water. The canyon’s main aquifers were too deep for ancient Chacoans to use. Only smaller, shallower sources supported the springs that provided water for them. Today, aside from occasional stormwater flowing through arroyos, there is very little surface water—such as springs, pools, or wells—available.

Geology

After the supercontinent Pangaea broke apart during the Cretaceous period, the area became part of a changing region between a shallow inland sea called the Western Interior Seaway and a stretch of plains and low hills to the west. The coastline, made of sand and swamps, moved back and forth between east and west, repeatedly covering and uncovering the land that now lies on the Colorado Plateau where Chaco Canyon is located.

The Chaco Wash flowed over the top layers of what is now a 400-foot (120 m) high area called Chacra Mesa. Over millions of years, the flowing water carved a wide canyon into the mesa. The mesa is made of sandstone and shale layers from the Late Cretaceous period, which belong to the Mesaverde Group. Erosion further shaped the canyon’s bottom, revealing Menefee Shale bedrock. This bedrock was later covered by about 125 feet (38 m) of sediment. The canyon and mesa are part of the "Chaco Core," a distinct area different from the wider Chaco Plateau, which is a flat grassland with scattered trees. The Continental Divide is located 15.5 miles (25 km) east of the canyon, and this location, along with differences in drainage patterns and rock types, separates the Chaco Core from nearby areas such as the Chaco Slope, Gobernador Slope, and Chuska Valley.

Climate

Chaco Canyon and the surrounding area are dry places with scrubland and desert grasslands. These regions receive about 8 inches (200 mm) of rain each year, while the park gets an average of 9.1 inches (230 mm). Chaco Canyon is located on the side of mountains that faces away from the wind, which creates a rainshadow effect. This effect causes the area to have very little rainfall. The region has four clear seasons. Rain is most common from July to September, and May and June are the driest months. Most summer and winter rain comes from orographic precipitation, which happens when storm systems move up nearby mountains, releasing moisture as rain. Higher elevations receive more rainfall.

Chaco Canyon experiences extreme weather changes. Temperatures can range from −38 °F (−39 °C) to 102 °F (39 °C), and may change by 60 °F (33 °C) in one day. The area has fewer than 150 days without frost each year. The local climate changes greatly from years with lots of rain to years with long droughts. The El Niño–Southern Oscillation, a weather pattern that affects rainfall and temperatures worldwide, strongly influences the canyon’s unpredictable climate.

Flora and fauna

The plants in the Chacoan region are similar to those found in other high desert areas of North America. Sagebrush and several types of cactus grow alongside dry scrub forests made up of piñon and juniper trees, with juniper trees mainly found on the tops of mesas. The canyon is much drier than other parts of New Mexico at the same latitude and elevation, and it does not have the temperate coniferous forests that are common to the east. In the past, the area had few plants and animals, and this scarcity may have been caused by overpopulation, farming, hunting, destruction of habitats, and drought. These factors might have led the Chacoans to remove wild plants and animals from the canyon. It is believed that even during wetter times, the canyon could only support about 2,000 people.

Among the mammals in the Chacoan region, coyotes (Canis latrans) are common. Mule deer, elk, and pronghorn also live in the canyon, though visitors rarely see them. Other important animals include bobcats, badgers, foxes, and two types of skunks. The park has many rodents, including several prairie dog colonies. Small groups of bats live there during the summer. Because water is scarce, only a few bird species are found in the canyon. These include roadrunners, large hawks like Cooper's hawks and American kestrels, owls, vultures, and ravens. These birds are less common in the canyon than in the wetter mountain areas to the east. Smaller birds, such as warblers, sparrows, and house finches, are more numerous. Three types of hummingbirds live in the area, including the small but aggressive rufous hummingbird, which competes strongly with the calmer black-chinned hummingbird for nesting areas near water. Prairie rattlesnakes are sometimes seen in the backcountry, but skinks and other lizards are much more common.

History

The first people in the San Juan Basin were hunter-gatherers called the Archaic–Early Basketmaker people. These small groups came from nomadic Clovis hunters who arrived in the Southwest around 10,000 BC. More than 70 campsites from this time, dated to between 7000 and 1500 BC, were found in places like Atlatl Cave and Chaco Canyon. These sites had stone chips and other remains, with some located near an exposed arroyo in the canyon. The Archaic–Early Basketmaker people moved from place to place or lived in semi-permanent groups. Over time, they began making baskets to store gathered plants. By the end of this period, some people started growing food. Excavations showed they made tools, gathered plants, and hunted animals. Storage pits made with stone slabs suggest they began settling in one place more often.

By 900 BC, Archaic people lived at Atlatl Cave and similar sites. DNA evidence shows that people from the Picuris Pueblo once lived in Chaco Canyon. By AD 490, descendants of those who lived in Chaco Canyon, from the Late Basketmaker II period, farmed near Shabik'eshchee Village and other pit-house settlements.

A small group of Basketmakers remained in the Chaco Canyon area. Their culture developed over time, reaching its peak around 800 AD during the Pueblo I period. During this time, they built crescent-shaped stone structures with four to five homes next to underground rooms called kivas, which were used for ceremonies. These buildings are typical of the Early Pueblo People. By 850 AD, the Ancient Pueblo population grew rapidly, living in larger, more crowded pueblos. Evidence shows a turquoise processing and trading industry existed in the canyon from the 10th century. Around that time, the first part of Pueblo Bonito was built—a curved row of 50 rooms near its current north wall. Studies of skeletons from high-status graves in Pueblo Bonito found that members of an elite family were buried there for about 330 years between 800 and 1130 AD, suggesting a tradition of passing leadership through women, similar to practices in many Pueblo nations today.

The Chacoan system began to break down around 1140 AD, possibly because of a severe 50-year drought that started in 1130. Later, from 1250 to 1450, the region faced repeated droughts and unstable weather. Poor water management caused erosion and deforestation, forcing people to bring building materials from distant mountain ranges like the Chuska Mountains, over 50 miles away. Outlying communities began to leave, and by the end of the 12th century, buildings in the central canyon were sealed and abandoned.

Some experts believe that violence and warfare, possibly including cannibalism, may have caused people to leave. Evidence includes dismembered bodies found at two sites in the central canyon. However, Chacoan buildings were not built for defense, and few showed signs of burning from enemy attacks. Archaeological and cultural evidence suggests that people from this region moved south, east, and west into valleys near the Little Colorado River, the Rio Puerco, and the Rio Grande. Anthropologist Joseph Tainter wrote about the rise and fall of the Chaco civilization in his 1988 book The Collapse of Complex Societies.

Numic-speaking peoples, such as the Ute and Shoshone, arrived on the Colorado Plateau in the 12th century. Later, in the 15th century, Southern Athabaskan-speaking peoples like the Apache and Navajo moved into the area. They adopted Chacoan customs and farming techniques. Ute groups also visited the region for hunting and raiding. Today, the Navajo Nation is located west of Chaco Canyon, with many Navajo people living nearby.

The first recorded visit to Chaco Canyon was in 1823, led by New Mexican governor José Antonio Vizcarra during Mexican rule. He noted large ruins in the canyon. In 1832, American trader Josiah Gregg described Pueblo Bonito as built from "fine-grit sandstone." In 1849, a U.S. Army group passed through after the U.S. gained control of the Southwest following the Mexican War. Due to its remote location, the canyon was rarely visited for the next 50 years. In the 1870s, Smithsonian scholars did some initial studies, and formal archaeology began in 1896 when the Hyde Exploring Expedition from the American Museum of Natural History started excavating Pueblo Bonito. Over five summers, they sent more than 60,000 artifacts to New York and set up trading posts in the area.

In 1901, Richard Wetherill, who had worked with the Hyde Expedition, claimed land that included Pueblo Bonito, Pueblo del Arroyo, and Chetro Ketl. While investigating his claim, federal agent Samuel J. Holsinger described the canyon’s landscape, noted ancient roads and stairways near Chetro Ketl, and documented old dams and irrigation systems. His report, which urged the creation of a national park, was not published or acted on.

In 1902, Edgar Lee Hewett, president of New Mexico Normal University, mapped many Chacoan sites. Hewett and others helped pass the Federal Antiquities Act of 1906, the first U.S. law to protect ancient relics. This law was partly a response to Wetherill’s controversial actions, including unprofessional excavations and using ruins for building materials. The law also allowed the president to create national monuments. On March 11, 1907, President Theodore Roosevelt declared Chaco Canyon a National Monument. Wetherill gave up his land claims.

In 1920, the National Geographic Society began studying Chaco Canyon and hired Neil Judd, then 32, to lead the project. After a short survey, Judd proposed excavating Pueblo Bonito, the largest ruin. From 1921 to 1925, Judd’s team removed over 100,000 tons of dirt using 35 or more Native American workers, 10 white men, and eight or nine horses. They found only 69 hearths, which was surprising because Chaco is very cold in winter. Judd sent 90 tree samples to A. E. Douglass for dating, which helped create a timeline for construction at Chaco. Most beams used in the buildings were cut between 1033 and 1092 AD, the height of construction there.

In 1949, the University of New Mexico gave land to expand Chaco Canyon National Monument. In return, the university kept research rights to the area. By 1959, the National

Management

The National Park Service, a government agency in the Department of the Interior, manages Chaco Culture National Historical Park. The Bureau of Land Management controls nearby federal lands that include Chacoan roads. In 2002-2003, the park's annual operating budget was $1.434 million. The park's visitor center includes a museum called the "Chaco Collection Museum," which has not been open since 2017, along with an information desk, theater, bookstore, observatory, and gift shop. Visits to the Chaco Collection at the Hibben Center on the University of New Mexico's campus can be arranged by appointment. Before the 1980s, many excavations in the park were very thorough, with walls being torn down and thousands of items taken. In 1981, a new method, based on Hopi and Pueblo traditions, was used to stop these activities. Methods like remote sensing, studying Native American stories, and using tree ring analysis were used without disturbing the relics. In 1991, the "Chaco American Indian Consultation Committee" was created to allow Navajo, Hopi, Pueblo, and other Native American leaders to have a say in managing the park.

Today, the park's policy includes partially restoring excavated areas. One method is "backfilling," which involves covering the sites with sand. Other efforts aim to protect the park's historic atmosphere, like the "Chaco Night Sky Program," which reduces light pollution affecting the night skies. The program allows about 14,000 visitors each year to use the Chaco Observatory, telescopes, and astronomy activities. In 2013, the park was named a Gold-tier Dark Sky Park by the International Dark-Sky Association. Ancient relics outside the park have faced threats from development. For example, in 1983, plans to mine coal in the San Juan Basin near the park were proposed. This mining could have damaged the ancient roads. The "Chaco Roads Project" studied these roads, leading to their protection from mining. Because important archaeological sites are outside the park, the U.S. Department of the Interior plans to create a 10-mile buffer zone around the park to prevent development.

Sites

The Chacoans built their structures along a 9-mile (14 km) area of canyon floor. Some buildings were aligned with the four main directions (north, south, east, and west), while others were aligned with the 18.6-year cycle of the moon's highest and lowest points in the sky.

The central part of the canyon has the largest Chacoan buildings. The most studied is Pueblo Bonito. It covers nearly 2 acres (0.81 ha) and has at least 650 rooms. It is the largest great house, and in some parts, it was four stories tall. The builders used a special building method with thick walls made of stone and mortar. Pueblo Bonito is divided into two parts by a wall that runs exactly north to south, splitting the central plaza. A large kiva was placed on each side of the wall, creating a balanced design common in many Chacoan buildings. The size of Pueblo Bonito was similar to the Colosseum in Rome. Nearby is Pueblo del Arroyo, built between AD 1050 and 1075 and completed in the early 12th century. It is located near a drainage area called South Gap.

Casa Rinconada, far from other central sites, is located on the south side of Chaco Wash, near a road leading to a set of steep stairs that reach the top of Chacra Mesa. Its only kiva stands alone, with no homes or support buildings nearby. It once had a 39-foot (12 m) passage connecting the underground kiva to above-ground areas. Chetro Ketl, near Pueblo Bonito, has the typical "D"-shape of many central buildings. It was built between 1020 and 1050 and has 450–550 rooms sharing one large kiva. Experts estimate it took 29,135 hours of work to build Chetro Ketl alone. It is believed that 5,000 trees and 50 million stone blocks were used for construction.

Kin Kletso ("Yellow House") is a medium-sized building located 0.5 miles (800 m) west of Pueblo Bonito. It shows strong evidence of being built and used by people from the northern San Juan Basin. Its rectangular shape and design are similar to the Pueblo II cultural group, not the Pueblo III style or Chacoan variant. It has 55 rooms, four ground-floor kivas, and a two-story tower that may have been used as a religious center. Evidence of an obsidian-processing industry was found near the village, which was built between 1125 and 1130.

Pueblo Alto is a great house with 89 rooms located on a mesa top near the middle of Chaco Canyon, 0.6 miles (1 km) from Pueblo Bonito. It was built between AD 1020 and 1050 during a time of widespread construction in the canyon. Its location made the community visible to many people in the San Juan Basin. It was only 2.3 miles (3.7 km) north of Tsin Kletzin, on the opposite side of the canyon. Pueblo Alto was the center of a bead- and turquoise-processing industry that influenced other villages in the canyon. Chert tools were commonly made there. Research by archaeologist Tom Windes suggests only a few families, perhaps five to twenty, lived in the complex. This may mean Pueblo Alto was used mainly for non-residential purposes. Another great house, Nuevo Alto, was built on the north mesa near Pueblo Alto in the late 12th century, a time when the Chacoan population was shrinking.

Another group of great houses is in the northern part of Chaco Canyon. Among them is Casa Chiquita ("Small House"), built in the 1080s during a time of heavy rainfall when Chacoan culture was growing. Its design is smaller and more square-shaped, and it lacks the open plazas and separate kivas of earlier buildings. Larger, square-shaped stones were used in its construction, and the kivas followed the northern Mesa Verdean style. Two miles down the canyon is Peñasco Blanco ("White Bluff"), an arc-shaped building built on the canyon's southern rim in five stages between 900 and 1125. A nearby cliff painting called the "Supernova Platograph" may show the sighting of the SN 1054 supernova on July 5, 1054.

Hungo Pavi, located 1 mile (1.6 km) from Una Vida, had a circumference of 872 feet (266 m). Early studies found 72 ground-level rooms, with buildings reaching four stories tall. One large circular kiva has been identified. Kin Nahasbas, built in the 9th or 10th century, is slightly north of Una Vida, at the foot of the north mesa. Limited digging has been done there. Tsin Kletzin ("Charcoal Place"), a compound on Chacra Mesa above Casa Rinconada, is 2.3 miles (3.7 km) south of Pueblo Alto, on the opposite side of the canyon. Nearby is Weritos Dam, a large earthen structure that scientists believe provided Tsin Kletzin with water. The dam worked by holding stormwater in a reservoir. Heavy silt from flash floods forced residents to rebuild the dam and clean the area regularly.

Deeper in the canyon, Una Vida ("One Life") is one of the oldest great houses. Construction began around 900. It has at least two stories and 124 rooms. It shares an arc or D-shaped design with Peñasco Blanco and Pueblo Bonito but has a unique "dog leg" addition due to the land's shape. It is located in one of the canyon's major side drainages, near Gallo Wash, and was greatly expanded after 930. Wijiji ("black greasewood"), with just over 100 rooms, is the smallest great house. Built between 1110 and 1115, it was the last Chacoan great house built. It is somewhat isolated in a narrow wash and is 1 mile (1.6 km) from Una Vida. Even farther north are Salmon Ruins and Aztec Ruins, located on the San Juan and Animas Rivers near Farmington. These were built during a 30-year wet period starting in 1100. About 60 miles (97 km) directly south of Chaco Canyon, on the Great South Road, is another group of outlying communities. The largest, Kin Nizhoni, is on a 7,000-foot (2,100 m) mesa surrounded by marshy land.

Casamero Pueblo is located on McKinley County Road 19, near Tecolote Mesa, a red sandstone mesa. It was connected to its nearby site, Andrews Ranch, by a Chacoan road. Chaco Canyon, Aztec

Ruins

Large buildings called "great houses" were central to religious activities in Chaco Canyon. The Chacoans used building methods that were unusual for their time, and their structures lasted for many decades or even centuries. As architectural styles changed over time, the great houses kept some important features. One key feature was their large size; these complexes often had more than 200 rooms, with some containing up to 700 rooms. Individual rooms were larger than those in earlier Ancestral Puebloan buildings, with higher ceilings. The buildings were carefully planned, with large sections completed in one step instead of being built in stages. Most houses faced south, and open areas called plazas were surrounded by buildings with sealed rooms or high walls. Some houses were four or five stories tall, with single-story rooms near the plaza. Room blocks were built in steps, so the tallest parts formed the back of the structure. Rooms were often grouped into sections, with larger rooms in the front and smaller ones in the back or for storage.

Special buildings called kivas were built based on the number of rooms in a pueblo. One small kiva was built for every 29 rooms. Nine complexes each had a large kiva, up to 63 feet (19 meters) wide. All Chacoan kivas had T-shaped doorways and stone lintels. While some walls were simple or compound, most great houses used core-and-veneer walls. These walls had two parallel outer walls made of flat sandstone blocks held together with clay mortar. The space between the walls was filled with rubble, forming the core. Then, small sandstone pieces were covered in a layer of mud to create the outer surface. These stones were often arranged in special patterns. Building the great houses required the wood from 200,000 conifer trees, most of which were carried by people from mountain ranges up to 70 miles (110 kilometers) away.

The carefully planned buildings in large Chacoan complexes were built around AD 1030. The Chacoans combined pre-designed layouts, star and moon alignments, geometry, landscaping, and engineering to create unique public buildings. Researchers believe the great houses may have been occupied by a small number of people most of the time, with larger groups gathering only for yearly ceremonies. Smaller sites, like Hillside Ruin, were likely more for living and are found near the great houses in and around Chaco. The canyon itself lines up with a lunar alignment path, suggesting the location was chosen for its connection to the stars. This alignment also matched other important structures in the canyon.

Turquoise was very important to the people of Chaco. About 200,000 pieces of turquoise have been found at Chaco Canyon, and places where turquoise beads were made have been discovered. Turquoise was used for burial items, ceremonies, and other purposes. More than 15,000 turquoise beads and pendants were found in two burials at Pueblo Bonito. Some evidence suggests turquoise was traded widely.

Around this time, the Ancestral Puebloan people had a large population and built many structures. From the 10th century, Chacoan building methods spread from the canyon to nearby areas. By AD 1115, at least 70 other pueblos with Chacoan designs had been built in the San Juan Basin, covering 25,000 square miles (65,000 square kilometers). Experts think these buildings, some as large as the great houses, may have served purposes beyond farming, such as trade or ceremonies.

Thirty of these buildings, spread over 65,000 square miles (170,000 square kilometers), are connected to the central canyon and each other by six mysterious road systems. These roads stretched up to 60 miles (97 kilometers) and were built in straight paths. They had wide, scraped areas made of caliche, and sometimes walls or earthen barriers marked their edges. When needed, the roads included stone steps or ramps to cross hills or other obstacles. While their exact purpose is unknown, some archaeologists think the roads may have been used to transport wood.

Archaeoastronomy

Two spiral-shaped carvings near the top of Fajada Butte form a petroglyph called the "Sun Dagger," which is located behind the rock panels known as the "Three-Slab Site." These carvings are important symbols.

The petroglyph includes two spirals—one main and one smaller. The smaller, left-hand spiral marked both the spring and fall equinoxes. A beam of light, filtered through the slabs, revealed this design by splitting the spiral into two parts. The larger spiral to its right was lit by the "sun dagger," a beam of sunlight that bisected it during the summer solstice, when the sun reaches its highest point in the sky. According to Anna Sofaer, the artist who discovered the "Sun Dagger," the Chacoans used this site to mark "the middle of time." Each of the 9.25 turns in the large spiral represents one year in the 18.6-year cycle of the rising mid-winter full moon. A shadow cast by a slab marks each ring of the spiral as the full moon moves over time. When the full "minimum moon," closest to the winter solstice, rises, the shadow's edge hits the center of the spiral. Over time, the shadow moves outward, ring by ring, until it reaches the outer edge during the full "maximum moon," also in mid-winter.

Fajada Butte has five other petroglyphs, including a "rattlesnake" carving, other spirals, and a rectangle. These carvings are highlighted by contrasts between sunlight and shadows during equinoxes or solstices. Public access to the butte was limited in 1989 because erosion from foot traffic caused one of the three slabs at the "Sun Dagger" site to shift out of its original position. This movement reduced the site's accuracy as a solar and lunar calendar. In 1990, the slabs were stabilized and placed under observation, but the displaced slab was not returned to its original position.

Some theories suggest that at least 12 of the 14 main Chacoan structures were built and aligned together, with each oriented along axes that reflected the movement of the sun and moon at key times. Casa Rinconada, the first known structure with precise proportions and alignment, had twin T-shaped portals in its great kiva that were aligned north-south. Lines connecting opposing windows were within 10 cm of its center. The great houses of Pueblo Bonito and Chetro Ketl were found to be aligned along a precise east-west line, capturing the path of the equinox sun. Lines perpendicular to their main walls were aligned north-south, possibly reflecting the equinox midday sun. Pueblo Alto and Tsin Kletsin were also aligned north-south. These two directions form an inverted cross when viewed from above. The Great North Road, a straight pilgrimage route extending 35 miles north from Pueblo Alto, is believed by modern Pueblo people to symbolize myths about their arrival from the distant north.

Two structures, Pueblo Pintado and Kin Bineola, located 15 miles from the central canyon, lie along paths that align with the rising and setting of the full mid-winter "minimum moon," which occurs every 18.6 years. Two other structures, Una Vida and Peñasco Blanco, are closer to Pueblo Bonito and aligned with the path of the full "maximum moon." The terms "minimum" and "maximum" describe the extreme positions of the full moon's movement relative to true north. It takes about 9.25 years for the full moon near the winter solstice to move from its northernmost to southernmost position.

Speculation about the reasons for these alignments has been discussed by researchers, including Phillip Tuwaletstiwa of the U.S. National Geodetic Survey, in The Mystery of Chaco Canyon.

Gallery

• Chaco Prehistoric Stairway, Chaco National Cultural Historic Park, New Mexico
• Chaco Kiva Detail, Chaco Culture National Historic Park, New Mexico
• Chaco interior wall, showing log and stone used in building, Chaco Cultural Historic Park, New Mexico
• Early Graffiti, Chaco Culture National Historic Park, New Mexico
• Chaco Pictograph, Chaco Culture Historical Park, New Mexico
• Pueblo Bonito viewed from a distance