Geologic Tour of New Mexico — Physiographic Provinces

The craggy gray granodiorite spire of Cookes Peak, the highest point in the Cookes Range at 8,404 feet, is a prominent landmark in southwestern New Mexico. Cookes Spring on the southeast side of the range is one of just a few perennial springs in this part of New Mexico; consequently, this peak was an important marker of water for Native American, Spanish, and American travelers through the region during the 19th century. The peak was named for Captain Phillip St. George Cooke, who led the Mormon Battalion through southern New Mexico during the winter of 1846 while scouting an overland wagon route for the U.S. Army. Later, a Pony Express mail station was established near the spring. Fort Cummings was built nearby in 1863 to protect travelers from Apache attacks; the fort was manned by the U.S. Army off and on until Geronimo surrendered in 1886. Ruins of the Cookes Spring Station of the Butterfield Trail and Fort Cummings are located about a mile south of the present-day Hyatt Ranch.

Fort Union was established in 1851 to provide a much-needed military presence to travelers on the Santa Fe Trail. The trail had been active since 1821, when much of what is now New Mexico became U.S. territory in 1848, at the end of the Mexican War. Fort Union’s spectacular location on the western edge of the Great Plains was a strategic one, sited as it was near the junction of the Mountain Branch of the Santa Fe Trail with the Cimarron Cutoff. Between 1851 and 1891 Fort Union contained the largest American military presence in the Southwest; over 1,600 troops were stationed there in 1861. In 1878 the railroad came to New Mexico over Raton Pass, and by 1891 Fort Union had been abandoned. Visitors to the national monument can see some impressive historic ruins, including the foundations and adobe walls of many of the original buildings, and remnants of the deeply-rutted Santa Fe Trail.

Oliver Lee Memorial State Park, at the mouth of Dog Canyon on the western escarpment of the Sacramento Mountains, opened in 1980, but the area has attracted visitors for several thousands of years. The 180-acre state park has a flowing stream and forms an oasis on the edge of the harsh desert of the Tularosa (Spanish, "reddish willows") Valley. The park is named for Oliver Lee (1865-1941), a prominent rancher and state legislator who settled near the mouth of Dog Canyon in the late 1880s. Lee was active in developing water-control projects in the area. Oliver Lee's ranch is one of the many exhibits at the state park. The Visitor's Center houses displays of the geologic and cultural history of the canyon area. Approximately 30,000 people enjoy camping, hiking, and picnicking in the park each year. An interpretative trail along lower Dog Canyon allows visitors a glimpse of vegetation and wildlife in the oasis as well as several cultural sites. The Dog Canyon Trail starts at an elevation of about 4,500 ft in the state park and climbs the steep escarpment of the Sacramento Mountains to the Eyebrow Trail to Joplin Ridge at an elevation of 7,753 ft, for a total one-way distance of about six miles.

The 64-mile stretch of narrow gauge railroad track between Antonito, Colorado and Chama, New Mexico was originally built in 1880 as part of the Denver and Rio Grande Western Railroad. This rail line provided much-needed transportation and freight service between Denver and mining camps in Silverton during the late nineteenth and early twentieth centuries. When the Federal Government discontinued the use of the silver and gold standard to back American currency, the "Silver Panic" in 1893 caused the closure of many of the mines in the Silverton area. The railroad continued to operate with revenues from transportation of livestock, timber, and farm produce. The oil and gas industry in the Four Corners region also utilized the railroad. Demand for rail transportation in this region waned by the mid-twentieth century. Passenger service on the Denver and Rio Grande Western Railroad ended in 1951 and freight service ended in 1968. Railroad enthusiasts and legislative bodies in New Mexico and Colorado recognized the scenic splendor of the train route between Chama and Antonito. Through a joint effort, the Cumbres and Toltec Scenic Railroad, complete with coal-powered steam engines carrying tourists in railcars on refurbished narrow gauge tracks, was created in 1970 to preserve this historic and picturesque section of railroad.

The Valles Caldera National Preserve is one of the most geologically unique and significant areas in North America. The preserve encompasses much of the Valles caldera, a huge volcanic crater that formed 1.2 million years ago during an enormous volcanic eruption that spread ash over large parts of New Mexico. The caldera is located near the summit of the Jemez Mountains, a large volcanic complex in north-central New Mexico. The Valles caldera exhibits world-class examples of the landforms produced by a very large, explosive volcano, and the preservation and exposure of geological features within the Valles is spectacular. Much of what geologists know about large-scale explosive volcanism began with detailed studies of the rocks in the Valles caldera and Jemez Mountains, and the area continues to draw geologists from around the world. Since the eruption 1.2 million years ago, there has been uplift of the crater floor, followed by the eruption of smaller, younger volcanoes called “domes” within the crater left by the large eruption. Since then, the caldera has from time to time been home to a series of large lakes. This dynamic geological history is responsible for the beautiful and unique landscape that we see in the region today.

El Morro, which means "bluff" or "headland" in Spanish, is an imposing cliff made of Middle to Late Jurassic (155 to 165 million years old) Zuni Sandstone capped by Late Cretaceous Dakota (~95 to 96 million years old) sandstone and shale. Travelers, including Native Americans, Spaniards, and citizens of the United States, have carved their symbols, names, messages, and dates of their passage into the soft cross-bedded Zuni Sandstone for centuries.

Fenton Lake State Park is in the Jemez Mountains on the west side of the Valles and Toledo calderas, large collapse features that formed during voluminous volcanic eruptions 1.6 and 1.25 million years ago. The landscape around Fenton Lake is characterized by broad, grass-covered valley bottoms that lie between dissected orange-brown to white mesas that are bound by imposing cliffs. The cliffs are formed by the 1.6 to 1.25 million year old outflow sheets of Bandelier Tuff that erupted from the calderas. The south-flowing Rio Cebolla (Spanish word for onion), which feeds Fenton Lake, cut one of the broad valleys after 1.25 million years ago.

The Carrizozo Malpais are one of the youngest volcanic features in the state of New Mexico. The Malpais, which are the 75 km-long black feature in the satellite image, are basaltic lava flows, such as are being erupted today in Hawaii. State highway 380 traverses the Carrizozo Malpais, and this road provides good access to people who want to view, or visit the lava flows. The Valley of Fires Recreation Area is located on the Carrizozo Malpais.

Aztec Ruins National Monument was established in 1923 to preserve the remarkable remains of an ancestral Puebloan farming community, including a twelfth-century Chacoan great house. The settlement flourished from A.D. 1050–1150, at which time it was one of the largest Puebloan settlements in the Southwest, strategically situated between Mesa Verde to the north and Chaco Canyon to the south. Culturally it is considered a Chacoan outlier, at the northern terminus of one of the prehistoric roads that emanated from Chaco. Later occupants (in the 1200s) are thought to have had closer ties to Mesa Verde.

One of the earliest written eyewitness accounts of Aztec Ruins was provided by geologist John Newberry in 1859, who reported at that time that the walls stood 25 feet high. Both the ruins and the setting are spectacular, but the park is perhaps best known for the reconstructed Great Kiva, which was excavated in 1921 and reconstructed by Earl Morris in the 1930s. It is the only restored great kiva in the Southwest and is accessible to visitors; stepping inside provides a unique glimpse of what these ceremonial structures might have been like when they were intact. The park is now a World Heritage Site.

Kasha-Katuwe Tent Rocks National Monument is on the southeast side of the Valles and Toledo calderas, large collapse features that formed during voluminous eruptions in the Jemez Mountain volcanic field 1.61 and 1.25 million years ago. Tent Rocks encompasses a fascinating landscape in the southeastern Jemez Mountains. Kasha-Katuwe means 'white cliffs' in Keresan, the traditional language of the nearby Pueblo de Cochiti. Delicately layered sand, gravel, volcanic ash, and tuff of the Peralta Tuff Member of the Bearhead Rhyolite and sand and gravel of the Cochiti Formation, which are older units (2 to 6 Ma) in the Jemez Mountain volcanic field, have been erodedinto fragile to robust spires with balanced rocks perched on top. The hoodoos, erosional cones, and pedestal rocks that characterize Tent Rocks form as the result of differential erosion.