Prehistoric Trackways National Monument

A view at Prehistoric Trackways National Monument
A view at Prehistoric Trackways National Monument
Fossilized track found at Prehistoric Trackways National Monument

Prehistoric Trackways National Monument is a 5,280-acre property that was established in 2009 to conserve and protect a major deposit of Paleozoic Era fossilized footprints left behind up to 280 million years ago (predating the dinosaurs) by various reptiles, amphibians and insects. Mixed in with the footprints are fossilized plants and pieces of petrified wood. Some of the species represented were previously unknown. Prehistoric Trackways National Monument contains some of the most significant Early Permian track sites on Earth.

However, as new trackways are discovered, they are removed and taken to the New Mexico Museum of Natural History and Science in Albuquerque, so don't go to this property thinking you're going to see much of the ancient footprints. If you want to see the fossilized footprints, go the the museum in Albuquerque.

The property itself is located in the Robledo Mountains northwest of Las Cruces at a median elevation of 4,500'. The Robledo Mountains are a typical desert mountain range: heavily incised canyons in a steep mountainous terrain. The vegetation is dominated by creosotebush and cactus. Annual rainfall runs around 8.5", and most of that arrives in July, August and September in the form of thundershowers. There is the possibility of hiking, horseback riding and driving off-highway vehicles in some portions of the national monument. The property is open year-round and there are no fees involved.

To get there: make your way to Shalem Colony Trail, north of Las Cruces. On Shalem Colony Trail, just south of the bridge across the Rio Grande you'll find a dirt county road heading west (Rocky Acres Trail). Go about 1/4 mile on Rocky Trails Road until you come to another dirt road on the left heading west. Turn onto that, cross the cattle guard and continue west. You'll be on the property very quickly and after about 1 mile, you'll be wishing you were in a high-clearance 4WD vehicle...

Prehistoric Trackways National Monument is surrounded on three sides by the Desert Peaks unit of Organ Mountains-Desert Peaks National Monument.

Fossilized dinosaur footprints found at Prehistoric Trackways National Monument
Fossilized dinosaur footprints found at Prehistoric Trackways National Monument
Prehistoric Trackways National Monument map
Prehistoric Trackways National Monument map
Photos and map courtesy of the Bureau of Land Management

Geologic Time Scale

A view of the actual K-T Boundary embedded in the sandstone near Trinidad, Colorado
The K-T Boundary is that white band beneath the upper layer of sandstone
Subdivisions based on Strata/Age Radiometric Dates (millions of years ago)
Neogene 0-2
Paleogene 2-65
Laramide Orogeny 63-65
Cretaceous-Tertiary Extinction Event 65
Cretaceous 65-145
Jurassic 145-210
Triassic 210-255
Permian-Triassic extinction event 251-260
Permian 255-280
Alleghenian Orogeny 260-325
Carboniferous: 280-360
Pennsylvanian 280-320
Mississippian 320-360
Devonian 360-415
Silurian 415-465
Ordovician 465-520
Cambrian 520-540
Precambrian Eons 541-4600
Proterozoic 541-2,500
Archean 2,500-4,000
Hadean 4,000-4,600

The table to the right gives a rough breakdown of the geological ages of Earth as used in modern Geology texts.

Much of the oil and gas we use comes from vegetative deposits made during the Permian and Pennsylvanian (late Carboniferous) ages. A lot of the coal we use (with its accompanying methane gas) comes from the great jungles and forests of the Mississippian and Pennsylvanian (early and late Carboniferous) ages in the Paleozoic era. Big reptiles and dinosaurs lived out their lives during the Triassic, Jurassic and Cretaceous Periods of the Mesozoic Era.

It was at the end of the Cretaceous Age that the Laramide Orogeny was set in motion, the Colorado Plateau uplifted and the Ancestral Rocky Mountains built. That was also during the time when an asteroid impacted near the Yucatan Peninsula and tipped the environmental scale in a direction that wiped virtually all the dinosaurs from the face of the planet. The K-T Boundary is a thin layer of iridium that filled the atmosphere during that explosion, then fell back to Earth during the global fires and the atmospheric upheaval afterward. While there have been plenty of marine, insect, reptile, amphibian, plant and mammal fossils found from times since, there has never been a dinosaur fossil found from the years after that impact. The K-T boundary is accepted as the definitive marker between the Cretaceous and Tertiary Ages, the marker of the Jurassic extinction event.

The Permian-Triassic extinction event seems to have happened in two major pulses about 9 million years apart. During the Permian age many insect orders had grown huge. A rise in CO2 in the atmosphere led to a rise in temperature and to acidification of the oceans. Marine invertebrates with carbon-based skeletons suffered worst but this was also the only mass extinction that affected insects: eight or nine insect orders became extinct and ten more suffered greatly reduced diversity. Insects, however, had generally recovered by the late Triassic, everything but that giant size anyway. The second pulse seems to have occurred around the time of the Araguainha impact, an asteroidal impact in Brazil that was not large enough to set off catastrophic extinction by itself but it occurred in an area filled with oil shale and the resulting sudden rise in global warming from the fires that ignited may have begun the atmospheric cascade that led to ocean surface temperatures around 104°F (40°C). That high an ocean temperature meant it was too hot for many marine species to survive. When it was over, more than 70% of terrestrial species and almost 90% of marine species had died out. Some land ecosystems took 30 million years to recover.

Photo of the K-T Boundary courtesy of TheArmchairExplorer, CCA-by-SA 4.0 License