Bureau of Land Management
The country in northwestern New Mexico between Cuba and Farmington is a land of contrast. Flat grassy plains are cut by valleys that expose the multi-colored moonscapes that we call badlands. The largest area of badlands in the region that is readily accessible to the public is the Bisti/De-Na-Zin Wilderness, popularly known as the Bisti Badlands. The badlands are generally exposed in a series of east to west-trending valleys formed by the tributaries that feed to the south to the north-flowing Chaco River.
The many fossils preserved in this region make this one of the best places on Earth to study the fascinating story of the end of the age of dinosaurs and the beginning of the age of mammals. These fossils will not be obvious to casual visitors, but visitors will be instantly struck by the spectacular scenery of this area, which has been featured in books, magazines, calendars, and websites.
(WGS 84 or NAD 83)
The main access to the Bisti/De-Na-Zin Wilderness is 40 miles south of Farmington on NM 371. The turnoff is to the east on CR 7297 and is marked. Follow the gravel road for 2 miles to reach the dirt parking lot. You will intersect with a north-south dirt road (CR 7000). Cross this road and follow a track to the boundary fence. The most scenic area is now about a mile southeast. The most interesting geological features are the eroded white sandstones. There are many hoodoos or mushroom rocks where resistant rocks are preserved on pinnacles of softer rock that have been eroded back to form the “mushroom stalks.” The very hard, brown sandstones of the Bisti Member of the Kirtland Formation often cap very high pinnacles and sharp ridges in this area. Some of the highest brown peaks are used for nesting areas by ferruginous hawks.
Alternatively, turn west off US 550 at Huerfano Trading Post. This route is entirely on dirt roads (CR 7500 and CR 7023), which can be hard to follow and are impassable in wet weather. There are many unmarked turnoffs; the best advice is to follow the most heavily traveled dirt road
Northwestern New Mexico is on the edge of the Colorado Plateau, which includes most of northeastern Arizona, most of eastern Utah, and western Colorado. The Colorado Plateau is a part of North America that has stayed relatively rigid while the areas around it (such as the Rocky Mountains) have crumpled as the continent has collided with other parts of the Earth’s crust. In general the Colorado Plateau is characterized by high plateaus of flat-lying rocks that are spectacularly dissected by enormous canyons such as at Grand Canyon National Park or Canyonlands National Park. The edges of the Colorado Plateau are characterized by a series of saucer- shaped geological basins where the rocks slant towards the center of a depression. The San Juan Basin is one such saucer; it includes most of northwestern New Mexico and a portion of southwestern Colorado that extends nearly to Durango. The rocks of the Bisti area are on the western side of the basin, so they are tilted to the northeast at about 5 degrees.
The current San Juan Basin formed during the Laramide orogeny, the mountain-building event that formed the Rocky Mountains. A geologic basin looks like a bull’s eye from above, with concentric rings of rocks that are younger toward the center. The older rocks on the edges of the San Juan Basin are from the beginning of the age of dinosaurs (Triassic) and are about 220 million years old. Going toward the center we find rocks from the middle of dinosaur time (Jurassic) and the end of dinosaur time (Cretaceous). Finally, at the center of the bull’s eye we have rocks from the two time intervals that followed the extinction of the dinosaurs (Paleocene and Eocene). The Bisti Badlands expose rocks from the end of the Cretaceous and the Paleocene—from just before to just after the great dying that occurred at the Cretaceous/ Tertiary boundary.
The San Juan Basin also includes younger volcanic rocks, and it has a rich archeological record, particularly of the prehistoric Puebloans (the people we have for years referred to as the Anasazi), who built large stone complexes, including those at Chaco Canyon National Historical Park and Aztec Ruins National Monument.
The Rock Record
Geologists divide the thick sequence of rocks exposed in the Bisti Badlands into four main intervals or formations, which, starting from the oldest, are: (1) Fruitland Formation; (2) Kirtland Formation; (3) Ojo Alamo Formation; and (4) Nacimiento Formation. The oldest rocks occur in the southwest part of the Bisti Badlands and the layers become progressively younger to the northeast.
The Fruitland Formation is the most easily visible and forms arguably the most scenic, and certainly the most photographed, badlands close to NM 371. The Fruitland represents swamps and rivers that formed close to the Cretaceous shoreline about 74 million years ago. The rocks that formed in swamps and other poorly-drained areas are black coals and gray shales. The river channels are represented by white sandstones that provide a stark contrast to the drab colors of the other rocks. The sandstones are more resistant to erosion than the soft coals and shales, so they form resistant cliffs and ridges that are often sculpted by erosion into exotic shapes including those mushroom-shaped rocks commonly referred to as hoodoos. Other very hard rocks in the Fruitland are layers or concretions of iron minerals (mainly siderite) that vary in color from brown to purple.
Coal burns not only in fireplaces but also naturally. Whole seams of coal may catch fire and burn, baking the surrounding shales into a hard, red rock. Stripes of this “clinker” or “red dog” provide the only bright colors in the Fruitland Formation.
The overlying Kirtland Formation is also Cretaceous in age, although it is a little younger than the Fruitland. The Kirtland is easy to spot because it consists of thick sequences of shales and siltstones that are primarily shades of green in contrast to the grays of the Fruitland. The Kirtland only has a few very thin coals, less than a foot thick. The Kirtland does have a few white sandstones, but they are thinner than those in the Fruitland.
The Kirtland can be divided into three sequences: (1) a lower Hunter Wash Member that has a basal sandstone layer with a white base and a brown top (Bisti Bed) and consists mainly of drab green siltstones; (2) a middle Farmington Sandstone Member that includes sheet-like sandstones, many of which have brown tops; and (3) an upper De-na-zin Member that is similar to the Hunter Wash Member but includes purple beds near its top. Dinosaur and other fossil bones are scattered through the Kirtland.
The Ojo Alamo Sandstone is on top of the Kirtland and is mostly Cretaceous in age, although it extends into the lowest part of the Paleocene. The Ojo Alamo includes two starkly contrasting layers. The lower Naashoibito Member is a colorful interplay of purple mudstones and white sandstones, whereas the upper Kimbeto Member is a massive, cliff-forming brown sandstone. Fossils are abundant in the Ojo Alamo. The Naashoibito includes many bones of dinosaurs and other land animals (including turtles and crocodiles), whereas the Kimbeto contains only a few recycled dinosaur bones but spectacular fossil logs.
It is probable that the end of the Cretaceous and the extinction of the dinosaurs occurred somewhere near the Naashoibito/Kimbeto contact, at what we call “the K/T Boundary” (or the Cretaceous/Tertiary Boundary). The upper part of the Kimbeto Member is inter-layered with the Paleocene Nacimiento Formation, which contains remains of mammals who survived the great dying.
The Nacimiento Formation is a candy-striped unit of rock with whites, blacks, and red. These rocks are mainly shales and sandstones with some thin coaly beds. The rocks in the Bisti Badlands represent the lower Kutz Member. The Nacimiento has yielded the youngest animals in the Paleocene, which are globally important. The two earliest ages in the Paleocene are based on these mammals and are named the Puercan and Torrejonian for the Rio Puerco and Torrejon Wash in the San Juan Basin.
The rocks of the Bisti Badlands tell two dramatic and parallel stories: the final retreat of the ocean from New Mexico, and the extinction of the dinosaurs at the end of the Mesozoic. During much of the Cretaceous a narrow strip of sea split North America into two land masses. The western shoreline moved backward and forward through what are now the western states of New Mexico, Colorado, Wyoming, Arizona, Utah, and Montana. As the shoreline shifted, parts of New Mexico were (alternately) underwater, beach front properties, or dry land. Finally, as the Cretaceous drew to a close, the sea retreated northeastward out of New Mexico, leaving the northeastern corner last.
Coal forms from peat, which forms in swamps. Therefore, the coal-rich Fruitland Formation obviously represents an environment close to the shore, much like areas in the modern southeastern United States—the Mississippi delta and the Okefenokee Swamp, for example. As you go upward through the layers of Cretaceous rock there is less and less coal. This reflects the fact that the sea was retreating and that the Bisti area was getting farther and farther from the swampy coast. The Kirtland Formation represents flat river plains. The white and brown sandstones formed in the rivers and streams, and the green shales represent floods that dumped mud between them.
There are two intervals in the rock sequence that contain very high percentages of sandstone: the middle Farmington Member of the Kirtland Formation and the upper Kimbeto Member of the Ojo Alamo Sandstone. There are several ways that rivers can produce thick layers of sandstone with very little shale. The easiest explanation is that mountains were being pushed up and heavily eroded, which produced lots of sand. This may be the explanation for the Kimbeto Member; there was mountain building and volcanism occurring in southwest Colorado at the time it was deposited. The Farmington Member contains a lot more shale than the Kimbeto Member, but it has the same general origin.
At the end of the Cretaceous, a major catastrophe struck the Earth. A large meteorite several miles in diameter crashed into the sea near what is now the Yucatan Peninsula of Mexico, resulting in the Chicxulub Crater. Enormous quantities of dust were thrown into the air, and the surface of the Earth was covered by huge fires. The meteoritic dust eventually settled and created a thin (2–4 inch) layer of fine, whitish clay that is rich in elements that are common in meteorites but rare on the surface of the Earth, such as iridium. In the San Juan Basin, this clay layer has not been found, probably because of contemporaneous erosion. In northeast New Mexico the dust settled in quiet swamps and the iridium-rich layer can be found in several places around Raton including Sugarite Canyon State Park. The dust may not be preserved in the Bisti area, but the devastation of life that resulted in the extinction of the dinosaurs affected this area.
The dinosaurs that inhabited this area were dominated by two groups of herbivores. The most common animals were duckbilled dinosaurs or hadrosaurs, the most famous of which was Parasaurolophus. This bizarre animal looked as though it had a boomerang protruding from the back of its head. The other main group of herbivores was the horned dinosaurs. The most famous dinosaur of this type is the three-horned Triceratops, but it doesn’t occur any further south than Denver. In New Mexico we have a unique relative called Pentaceratops that has five horns. Other plant-eating dinosaurs include the armored dinosaurs or ankylosaurs, which include Nodocephalosaurus and bone-headed or pachycephalosaur dinosaurs such as Prenocephale. Meat-eating dinosaurs include Tyrannosaurus, Daspletosaurus, and Ornithomimus. The Cretaceous fauna also includes a variety of turtles, crocodiles, lizards, and mammals.
After the extinction of the dinosaurs the landscape was dominated by a variety of small mammals. Mammals had evolved at about the same time as dinosaurs during the Late Triassic (about 225 million years ago). Mammals living at the end of the Cretaceous included an extinct group of rodent-like animals called multituberculates, pouchedmarsupials, and a lesser number of placental mammals including our ancestors. Mammals did not suffer a major extinction at the end of the Cretaceous, but the relative numbers of groups changed. Paleocene faunas were dominated by placental mammals and marsupials, and multituberculates were much less common. Turtles, crocodiles, and lizards continued through the great dying with little change. The Nacimiento Formation that contains these Paleocene faunas represents river plains that formed when the climate was cooler and drier than during the Cretaceous.
The Bisti/De-na-zin Wilderness originally consisted of two separate wildernesses. The former Bisti Wilderness at the western end near NM 371 includes the strangely sculpted landscapes that are the favorites of both photographers and hikers. The Bisti/De-Na-Zin Wilderness includes 45,000 acres managed by the U.S. Bureau of Land Management. The Wilderness boundaries enclose three parcels of private Navajo land.
For more information, contact:
Bureau of Land Management
Farmington Field Office
6251 College Blvd., Suite A
Farmington, NM 87402