Geologic Tour of New Mexico

Organ Mountains–Desert Peaks National Monument is a large, diverse and recently established park. It has four separate geographic areas: the Organ Mountains, the Doña Ana Mountains, the Potrillo Mountains, and the “Desert Peaks." This tour deals only with the Organ Mountains. The geology of the Doña Mountains area is briefly discussed in the tour of Fort Selden–Leasburg Dam. The Potrillo Mountains include the remote Potrillo volcanic field and are covered in the Kilbourne Hole tour. The "Desert Peaks" includes the Robledo Mountains and Sierra de las Uvas. The Robledo region is described in the tour of the "Prehistoric Trackways National Monument" (a separate, but contiguous national monument).

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.

Angel Peak, a 7000-foot pinnacle capped by sandstone, is a prominent landmark near Bloomfield in northwestern New Mexico. It is in the northern part of the San Juan Basin, a large structural depression that formed starting about 75 million years ago during compressional Laramide deformation. The San Juan Basin was surrounded by mountainous uplifts to the north (now buried by the 35 to 20 Ma San Juan volcanic field in southwestern Colorado) and to the east that also formed by Laramide-related compression. The sediments that can be seen at Angel Peak National Recreation area were eroded off of the old Laramide highlands and deposited in the basin 50 to 65 million years ago. More recently, over the course of the last 5 million years (or less), the westward-draining San Juan River, a tributary to the Colorado River, has eroded the rocks of the San Juan Basin. Drainages feeding into the San Juan River have carved the scenic landscape we see today.

Tsiping, also called Tsi’pin or Tsi’pinouinge, is a remarkable pueblo ruin located on Pueblo Mesa near the village of Cañones in the northern Jemez Mountains. Although the site is on Santa Fe National Forest land, the site is off limits unless you have a permit. Permits can be obtained from the Coyote Ranger Station.

Tsi’pinouinge means “village of the flaking stone”, a reference to the village’s proximity to lithic-source quarries in the Pedernal Chert on Cerro Pedernal. Based on tree-ring measurements and ceramic styles, Tsiping was occupied between 1200 AD and 1325 AD, during the Classic Period. Tsiping was the northernmost and largest of the Classic Period pueblos. The village had somewhere between 335 to 400 ground floor rooms, sixteen kivas, and a central plaza. Cavate dwellings are located on the southeastern side of the mesa.

Rockhound State Park lies in the Little Florida Mountains southeast of Deming, New Mexico. It was established in 1966 as the first park in the United States that allowed collecting of rocks and minerals for personal use. Each visitor is allowed to collect as much as 15 lb of rocks and minerals from the 1,100-acre park; mineral dealers are not allowed to collect for sale. Rockhound State Park actually consists of two separate units, the main park and Spring Canyon Recreation Area. Spring Canyon lies in the northern Florida Mountains, south of the main park, and is open for day use only from Easter through November.

Caballo Lake State Park is located approximately 14 miles south of the town of Truth or Consequences. Caballo Reservoir is on the Rio Grande in south-central New Mexico east of Interstate 25 between Socorro and Las Cruces.

Camping, picnicing, and boating facilities are available at this state park. Caballo Lake State Park is the third largest state park in New Mexico. This park is generally quiet compared to Elephant Butte State Park to the north.

Monument Rock is located west of Socorro and north of U.S. Highway 60 in the eastern Sawtooth Mountains of Catron County, New Mexico. The area can be reached from Datil by traveling west along Highway 60, 12.3 miles to Forest Road 6A. Turn right on Forest Road 6A and drive north 3.7 miles to the prominent spire of Monument Rock.

The area can also be accessed from Pie Town by driving east along U.S. Highway 60 to Forest Road 316. Turn left onto Forest Road 316 and drive northeast 3.5 miles to Forest Road 6A. Turn left and drive 1.1 miles to Monument Rock.

Leasburg Dam State Park is adjacent to Fort Selden State Monument on NM–157 (Fort Selden Road) at the Radium Springs exit on I–25, north of Las Cruces. It is an area rich in both geologic and human history. The location was an ancient Indian campground and a crossing point for Spanish caravans headed across the Jornada del Muerto. Living-history demonstrations of 19th century military life at Fort Selden highlight many weekends during the summer. Wildlife viewing, especially bird watching, is popular at the state park. A bird list is available from the park office. In the winter months many species of ducks, teals, snow geese, cranes, herons, egrets, swans, and pelicans migrate through the southern Rio Grande valley and can be seen at the state park. Numerous raptors, including owls, turkey vultures, eagles, and hawks, can be seen hunting in the area. Small mammals common to the park include rabbits, squirrels, chipmunks, rodents, coyotes, and foxes.

Gila Cliff Dwellings National Monument is in the Mogollon Mountains approximately 44 miles north of Silver City, New Mexico. Gila Cliff Dwellings National Monument was established in 1907 and is one of the nation’s oldest monuments. The monument lies within the Mogollon-Datil volcanic field; volcanic eruptions from this field covered 40,000 km2 of southwestern New Mexico and southeastern Arizona with lava and ash flow tuffs 40 to 24 million years ago.

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.