White Ridge Bike Trails
A view from the top at White Mesa Bike Trails
The White Ridge Bike Trails are in the scenic and rugged countryside just southwest of the village of San Ysidro. The mountain bike trails here cross State land, Pueblo of Zia land and mostly BLM land. The BLM has obtained rights-of-way from the State and the Pueblo to provide these routes. Hikers are allowed to use the entire trail system, too, and horseback riders are allowed to use one designated segment.
White Mesa (Mesa Blanco) gets its name from the gypsum that most of the mesa is composed of. The gypsum was left over after the evaporation of an ancient sea that covered this area. On the western edge of the mesa are high, narrow mesa ridges, part of the plunging Tierra Amarilla Anticline. Geologically speaking, this is a very interesting area. Also exposed here is the Morrison Formation, a layer of rock laid down about 150 million years ago. The Morrison is filled with dinosaur fossils and large pieces of petrified wood, indicating that at one time, this area was covered with a forest frequented by dinosaurs. The fossilized skeleton of a Seismosaurus (the longest dinosaur skeleton ever recovered) was found just west of here in the Ojito Wilderness.
The nearest facilities and services are in the village of San Ysidro, about 6 miles northeast.
To get to the White Ridge Bike Trails: About 20 miles northwest of Bernalillo on US 550 (and about 2 miles south of San Ysidro), turn west on County Road 906 (Cabezon Road). Follow the left fork and go about 4.4 miles to the gravel parking area.
Maps: BLM - Albuquerque, Los Alamos
Another view at White Ridge Bike Trails area
Map of the White Ridge Bike Trails area
Geologic Time Scale
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)|
|Cretaceous-Tertiary Extinction Event||65|
|Permian-Triassic extinction event||251-260|
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.