Perea Nature Trail

A view in the beginning of the Perea Nature Trail
A view at the beginning of the Perea Nature Trail
Sign marking the Perea Nature Trail

The Perea Nature Trail is an easy one-mile loop trail along a mountain stream just outside the village of San Ysidro. During the walk you'll get some great views of the Jemez Mountains to the northeast and the Nacimiento Mountains to the north. The Nacimiento's are old mountains, while the Jemez are relatively new.

The Nacimiento's are formed of precambrian granite with a schist and gneiss core. That core is some of the oldest rock in New Mexico. The western slopes of the Jemez are composed of a white-to-tan sandstone, the Agua Sarca formation, laid down in the Triassic Age. Below the Agua Sarca is the Glorieta formation, grey sandstone laid down during the Permian Age. That sandstone has been compressed enough to now form cliffs where it is exposed. At the San Ysidro Fault, the slope turns into a brilliant red vertical face, striped with shades of red differentiating outcrops of the Abo and Yeso formations. The Abo formation indicates deposition along floodplains and river channels while the Yeso formation indicates shallow marine environments with deposits of local wind-blown sands.

To the southwest is Blanco Mesa, best known as a creative backdrop in photographs and motion pictures (although today it sees a lot of use as the White Mesa Bike Trails Area). In between Perea and Blanco Mesa is the Rio Salado riverbed with more than 100 million years of geology exposed. The upper layer is the Todilto formation, about 100 feet of white gypsum laid down over a brown limestone during the Jurassic Age. Below that is a layer of light tan-to-yellowish sandstone cliffs of the Entrada formation, hard sandstone laid down as ancient wind-blown sand dunes. The lowest formation exposed is the Chinle formation, a layer of mud-and-siltstones laid down in the Triassic Age.

Perea Nature Trail is also a walk through a riparian-wetland ecosystem. These ecosystems are important islands of environmental diversity, used by significantly more numbers of wildlife and livestock than their small sizes would suggest. Wetlands have a water table that is at or above the level of the surrounding land surface and provide sufficient water to grow plants that reduce the effects of flooding, remove pollutants and are especially good at processing carbon dioxide to produce oxygen.

The nearest facilities for modern humans are in the village of San Ysidro.

Along the Perea Nture Trail

To get to the Perea Nature Trail: About 20 miles northwest of Bernalillo on US 550 there's a brown state highway recreation sign posted at the turnoff. The access road is paved. The property is open year round and there are no fees involved.

Update 2015: I happened to be driving by one day and stopped to take a hike along the Perea Nature Trail. Whatever info I had gleaned from wherever about the place didn't do it justice: it was a very nice walk in an area that most likely sees a lot of birds passing through in season. But without stopping and enjoying that walk, I'd never have gotten these pictures either...

Maps: BLM - Los Alamos

Dropping down to cross a bridge
Dropping down to cross a bridge
A view of the riparian area
A view of the riparian area along the streambed
A view about one mile from the parking area
About one mile in from the parking area
Photos courtesy of TheArmchairExplorer, CCA-by-SA 4.0 License

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