The Door Trail

Accessible to people in wheelchairs.

Length of trail: Three-quarters mile (1.2 km) roundtrip

Location: Off Loop road 2 miles (3 km) east of Cedar Pass Visitor's Center.

Leisurely walking time: 45 minutes

Accessibility:About 100 yards of the trail is paved, providing wheelchair access to a badlands overlook beyond the Door. The remainder is too rough for wheelchairs, but it is relatively level, and careful hikers should have no difficulty. However, those who leave the trail will encounter steep-walled gullies and loose surface rock which makes footing treacherous..

Guide to the Door Trail

Stripes on the trail markers correspond to stripes opposite paragraphs in this booklet.
  1. A geological recipe for badlands includes easily eroded rocks, a climate too dry for heavy plant cover, extreme temperatures, and heavy rains once in a while. These ingredients are present here and have produced cliffs, jagged spires, and narrow cracks, which flare into gullies slashed deep into the surface.
  2. And yet one may look beyond this tumult to a flat and tranquil landscape of the past. About 27 million years ago the red clay-rich layer at eye level was a soil covered with plants. Many animals roamed a fertile plain, feeding, breeding, and ultimately dying. After being buried by sediment-loaded floods which swept in from mountains to the west, the red soil was fossilized. Geologists call a fossil soil a paleosol.

    How flat was the ancient plain?

    Focus your attention on the red layer in front of you, to the right, to the left, and exposed along the Badlands Wall through which you came via the Door. Everywhere, it lies at the same level relative to the other layers.

    We will encounter this fossil soil throughout our walk. It will serve as a reference point as we build up the story of how the material of the Badlands came to be here and how it is eroding away.

  3. The red paleosol (87 fossil soils have been identified in the park) is at eye-level but we walk upon a volcanic ash containing a small percentage of sand and clay mixed in. This mixture, after burial by sediments of later floods, formed rocks much harder than those made of clay. That is why the ash layer resists erosion while claystone layers above it have mostly vanished. The original sediment forming claystone was clay, and exposure to the weather turns it back into clay.

    Ash occurs throughout the Badlands formations. An ash layer, thinner than the one beneath our feet, caps the red fossil soil. Near the top of the Badlands Wall lies the greatest of all these ash deposits (look south and you can pick it out capping the higher buttes). Geologists have named it the Rockyford Ash; in places its depth is more than 30 feet. Only mamouth volcanic eruptions could have produced so much material.

    The ash in the Badlands was spewed into the atmosphere by distant volcanic eruptions west or southwest of the Badlands, and was transported here by the wind. Rainwater concentrated the fallen ash in low places where it lay even thicker than where it first fell.

  4. The ash is composed mostly of fine particles of glass. Slowly circulating ground water dissolved some of the quartz and also other minerals. In the vicinity of organic matter, or certain chemicals, the dissolved minerals came out of solution and cemented the ash into nodules ranging in size from small lemons to large melons. Occasionally, fossil bones are found partly or completely enclosed in a nodule.

    Many nodules are riddled by tiny holes about the diameter of a pencil. They have been called "worm holes," in the belief that they are trace fossils of creatures who burrows in streambed sediments. Others who study rocks suspect that they are trace fossils of plant roots.

    The iron mineral Hematite (Fe2O3) comprises slightly more than 3% of the Badlands ash deposits. In the presence of water, the hematite rusts and migrates to the surface of the nodules, staining them red.

  5. Erosion has removed almost all of the claystone and other layers that had been deposited above the ash layer we walk on. Surviving low mounds stand here and there, and around them are almost flat aprons of white clay. Flowing fast down the slopes, the rainwater transported the clay to the base of the mounds. On reaching the ash layer, which is almost level, the water slowed and the clay dropped out.

    These aprons of fine sediment are called miniature pediments. In some places in the Badlands, pediments are so nearly level and so white that they look like moats guarding the castle-like buttes they encircle.

  6. The ash layers resist erosion, but they are not immortal. At this level, erosion has had longer to work than at the freshly uncovered surfaces nearer the Wall. Claystone beneath the ash has caved in. The gullies have widened and cut deeper.

    Don't stand on the edge of the gullies. A misstep or a cave-in could send you tumbling, with painful consequences.

  7. Several gullies merged into a canyon which in form, if not in size and age, resembles the Grand Canyon of the Colorado. The Badlands change with every rain. The stream which snakes through the canyon may be dry today; only yesterday it was a raging torrent; tomorrow it will rage again.

    If you approach the edge for a better look, take care.

  8. The ash layer we have walked across is narrow here. Canyons squeeze in from either side. Cracks caused by earth movements make the surface look as though it were paved with carefully cut rectangular rock slabs. The cracks provide rainwater with openings through which to attack the claystone underneath.

    We face a surviving island of the red paleosol noted at the beginning of the trail. It is capped by a remnant of the same protecting ash layer we discussed earlier. Notice that here the ash consists of beds that slant from the top to bottom of each layer . This cross bedding indicates that a swift stream deposited the ash.

  9. We have reached Trail's End where two canyons merged and pinched off our peninsula of ash. But for the water that falls on the Badlands, and for the sediment it transports to the White River in the valley below, then on to the Missouri, and ultimately into the Gulf of Mexico, this spot is only a way station on a circle unbroken. As it circulates, the water evaporates, diffuses into the air, forms clouds, and presently falls again somewhere on the earth as rain or snow. Most of the water recycles within a few weeks, a few months, or a few years.

    The sediments take longer to recycle - millions, even billions of years. But eventually they are deposited, turned into rock, uplifted, eroded, and swept downstream again.

At Trail's End, we contemplate a landscape that tells us of the past, displays the present, and promises an ever changing future.

From the brochure published by the Badlands Natural History Society.

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© 1995 Karen M. Strom