New Mexico is a region rich in natural treasures. Though many are well-known, like White Sands National Park and Carlsbad Caverns, there are several that are overlooked, obscure, and/or relatively inaccessible.

Prehistoric Trackways National Monument is one of New Mexico’s lesser known geologic gems. Located in the Robledo Mountains north of Las Cruces, the monument encompasses 5,280-acres of undeveloped, high desert terrain at the north end of the Chihuahuan Desert. The U.S. Congress established the 5280-acre monument in 2009 to protect the fossilized trackways from the Paleozoic era. A local amateur paleontologist, Jerry MacDonald, found them in 1987.

Ancient Fossilized Footprints In the Robledo Mountains

Dimetrodon track fossil at Prehistoric Trackways National Monument
Dimetrodon track fossil at Prehistoric Trackways National Monument

Though fossilized footprints were spotted in the Robledo Mountains for decades prior to MacDonald initiating his search, he focused on gathering information about prior sightings from local hikers, fossil hunters, and quarrymen, ultimately finding an area that was covered with a dense concentration of trace fossils left in the sand and mud during the Paleozoic era. MacDonald excavated three long trackways from the site, now known as the “Discovery Site,” toting 2,500 slabs of stone trackways out on foot. Most of those slabs are part of the Jerry MacDonald Paleozoic Trackways Collection, housed at the New Mexico Museum of Natural History and Science. There are also large slabs of trackways available at the Las Cruces Museum of Nature and Science, the Carnegie Museum of Natural History, and the Smithsonian.

Though there are other early Permian tracksites in the world, Prehistoric Trackways National Monument is noteworthy due to the sheer volume and variety of fossils. Some of the trackway panels preserve up to 50 consecutive prints from individual animals, with tracks from multiple species found together. In fact, Prehistoric Trackways National Monument is considered the “most scientifically significant Permian tracksite in the world.

Trace Fossils vs. Traditional Fossils

From “Traces of a Permian Seacoast” – “This Dimetropus track is actually a cast formed when sediment settled into a depression made by the animal’s foot. Turned upside down, this track is now convex, raised above the rest of the rock slab. Many such track casts are seen in the trackways of the Prehistoric Trackways National Monument.”

Whereas traditional fossils preserve the death of a creature, ichnofossils preserve evidence of life and activity, like the impressions of foliage, footprints, burrows, body impressions from nesting or sleeping, or drag marks from various parts of a creature’s body, like the tail, belly, or fins. Fossils that preserve tracks or traces of animal behavior are useful to scientists, because they provide clues about animal behavior, movement, and interactions, as well as information about the environment in which those animals lived.

For example, there are numerous tracks associated with the Dimetrodon, a meat eating, mammal-like creature that was 10 to 13-feet long, weighing up to 500 pounds. It was the T-Rex of its time, which was millions of years before T-Rex roamed the planet. Whereas scientists thought the Dimetrodon was a slow, lumbering predator, they re-evaluated their assumption based on the many tracks left in the Robledo Mountains. The tracks are set close together, with no belly scraping or tail dragging, which indicates the Dimetrodon moved considerably faster than they thought.

The Permian Period

The Permian Period was the last period of the Paleozoic Era. It began almost 300 million years ago and ended over 250 million years ago, which means the creatures who left tracks and traces at Prehistoric Trackways were eradicated millions of years before dinosaurs walked the earth.

The Permian Period ended with mass extinction. The process played out over millions of years. Approximately 95% of the species on earth during the Permian Period vanished. As is often the case, cataclysmic geologic forces and dramatic climate change played a role.

Pangea in the Permian Period

The earth during the Permian period was very different than the world we inhabit today. Glaciation was widespread when the Permian period began, with the southern hemisphere experiencing cyclical ice ages. Sea levels would rise and fall dramatically based on the ice sheets. However, the climate warmed up considerably throughout Permian Period, becoming increasingly hot and dry.

At that time, most of the planet’s land masses were fused into a supercontinent called Pangea. It covered more than 30% of the earth’s surface. A global ocean, known as Panthalassa, surrounded Pangea. About 200 million years ago, during the Jurassic period, the supercontinent began to fracture, eventually forming the Atlantic and Indian oceans, as well as the modern distribution of continents.

The Hueco Seaway in Southern New Mexico

Walchia frond trace fossil at Prehistoric Trackways National Monument
Walchia frond trace fossil at Prehistoric Trackways National Monument

New Mexico was located near the western, equatorial edge of Pangea during the Permian period. The Hueco Seaway, a shallow, tropical sea, covered most of what is now southern New Mexico. The sea was shallow, warm, clear, and calm, much like today’s Caribbean Sea, with extensive tidal flats. There were two seasons: wet/hot and dry/hot.

Most of New Mexico north of the Hueco Sea was covered by river floodplains with dense conifer forests dominated by Walchia. Walchia was an ancient conifer that looked similar to a modern Norfolk Pine. Though Walchia fossils are abundant throughout the monument, it is rare to find other varieties of plant fossils in this region. In the meantime, northern New Mexico featured highlands, the ancient ancestors of the Rocky Mountains.

Prehistoric Trackways During the Permian Period

Dimetrodon track fossil at Prehistoric Trackways National Monument
Dimetrodon track fossil at Prehistoric Trackways National Monument

Prehistoric Trackways Monument was located on what was the coastline of the Hueco Seaway. The red mud along the tidal flats captured the tracks and traces of creatures large and small: amphibians, reptiles, marine life, as well as trees and foliage.

Along the shorelines, mammal-like vertebrate animals preyed on other critters, like the carnivorous Dimetrodon, an ancient pre-mammalian creature that had a sail-like fin on its back. They were sort of the T-Rex of their time, which was millions of years before T-Rex arrived. Additionally, there were large plant eaters roaming the shore, like the 10-foot long Pareiasaurs, armored reptiles who weighed as much as 1000 pounds.

Overall, the monument has proven to be a fossilized Petrie dish for scientists studying the Permian period. The layers of mudstone reveal important details about the history of New Mexico and, in fact, the history of the planet. The ancient geology of New Mexico, including the mass extinction at the end of the Permian period, are directly related to the abundance of oil and gas resources in the Permian Basin. If you want to walk the coast of an ancient sea, check out Prehistoric Trackways National Monument next time you visit Las Cruces.

Prehistoric Trackways National Monument

Prehistoric Trackways National Monument

Bureau of Land Management
1800 Marquess St.
Las Cruces, NM 88005
(575) 525-4300

Prehistoric Trackways National Monument is located in the Robledo Mountains, north of Las Cruces. The monument is surrounded on three sides by the Desert Peaks unit of Organ Mountains-Desert Peaks National Monument. The area is about 4,500 feet above sea level. It is high desert landscape, dominated by creosote and cactus. Canyons and gullies cut deep into the mountains.

The area gets about 8.5 inches of rain per year on average. Most of the rainfall occurs between July – September. Afternoon thunderstorms are common and lightning can be hazardous for hikers, because there is no shelter. Also, it gets really hot in the summer. Prepare accordingly. Take ample water, sunscreen, hat, etc. and watch for snakes. You are more likely to run into snakes on the trail when it is cooler, like early morning or early evening.

There is no visitor center, facilities, interpretive signage, or even a sign to let you know where you should turn off of Shalem Colony Trail. However, there is a parking area with some information about the site and the trails near the trail heads. Though there is a road that goes beyond the parking area, it is rough. 4WD will probably be needed, particularly if there has been recent rainfall.

Usually open 24/7. No fees.

Prehistoric Trackways National Monument Maps

Prehistoric Trackways National Monument Brochure

Directions to Prehistoric Trackways

Coming from the North via I-25: Get off at the Doña Ana exit. From NM320, aka Thorpe Road, go west to US 85, then head north about 1/2 mile to Shalem Colony Trail and head west. Shalem Colony Trail curves south. Go about 1.5 miles until you cross the Rio Grande. Take a right on Rocky Acres Trail right after you cross the river. Go about 1/4 mile and turn left on the dirt road (Permian Track Road). There is a parking area by the trail head. Note: There is no sign on Shalem Colony Trail or Rocky Acres Trail.

Coming from the South (Las Cruces): Take Picacho Ave./Hwy 70 to Shalem Colony Trail. Head north on Shalem Colony Trail for about 5.5 miles. Turn west on Rocky Acres Trail BEFORE you cross the river. If you cross the river, you’ve gone to far. Otherwise, same as above once you are on Rocky Acres Trail. No signs. Take Rocky Acres Trail about 1/4 mile. There will be a dirt road on the left, Permian Track Road, that goes to the parking area for the trails.

Recreation Opportunities

The BLM allows hiking, horseback riding, and off-road vehicles in portions of the monument, with about 30-miles of trail. However, this area heats up in the summer months and there aren’t many opportunities to escape the sun’s glare. BLM forbids removal of fossils from the monument. If you find something, leave it there.

There are limited opportunities for viewing fossils if you don’t know what you are looking for and there are no interpretive signs on the trail. There is one small panel of trackways as an obvious payoff on the Discovery trail. However, the BLM offers a guided hike monthly with Colin Dunn, a BLM paleontologist. The hike takes about three hours.

Prehistoric Trackways National Monument

Additional Travel Resources

Visit Las Cruces
336 S. Main St.
Las Cruces, New Mexico 88001
(575) 541-2444

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