The Blood and Bones of the Desert

The pothole-- Shallow depressions in rocks, they collect rainwater and provide short-lived sources of hydration and breeding grounds for animals as diverse as insects and frogs and predatory mammals. Pothole is a broad term; for example, some slot canyons have deep holes in their floors, and these floors are often referred to as potholes. Here, I refer to a pothole as a depression a few inches deep atop a rocky surface.

Tanks/Tinajas/Huecos-- Tinaja is Spanish for a small pool in a rocky hollow (source). Hueco is Spanish for "hole, hollow, gap."Larger and deeper than the typical pothole but still ephemeral and too small to be counted even as a small pond (though some can be the size of a small pond), these, like the oases, are true desert gems. Erosion, usually water-based, carves bowls into rock surfaces. Then rainfall and snowmelt fill them. Depending on the climate and the depth, these tanks can hold water anywhere from days to months; some almost never go dry.

Tanks are not scarce but are nevertheless uncommon enough to be a real treat for the unsuspecting hiker or climber. Some, like Ernst Tinaja in Texas's Big Bend National Park, or the Calico Tanks in Red Rock Canyon National Conservation Area just outside Las Vegas, Nevada, are well-known and have popular trails leading to them. But many more, really most, await those who are willing to do a little wandering. The second one I ever saw (the first was Ernst Tinaja) was one I found purely by accident; in Arizona's Superstition Mountains, I had hiked a trail to a viewpoint and decided to take a more direct but more rugged way back, and along the way I found a deep-looking tank filled with dark water (see below).

These basins all play a critical role in the survival of wildlife. Even brine shrimp, known to some as sea monkeys, can make a life in them. In Nevada's Red Rocks, the tinajas help sustain the population of bighorn sheep. Life from algae to cougars finds sustenance in these places.

But they can also be graves. Smoothed out as they are from running water, including flash floods (many tanks have been scooped out of the floors of slot canyons, though some are atop desert mountains), tanks can be death sentences for those careless or unlucky enough to fall into them. At Ernst Tinaja, even deer and mountain lions have drowned. Humans have died in tanks and deep potholes, too.

Protecting the Tanks

In many places where tanks are found, regulations prohibit swimming and wading. The oils from the body can upset the ecological balance of these small worlds. Plus, for reasons outlined in the previous paragraph, it's just safer to look and not touch. Bottom line, whether regulations exist or not: it is best to do nothing more with the tanks than sit by them and/or photograph them. Don't put your short-term thrills ahead of the long-term health of a delicate ecosystem.

Bones

The bones are the structure that supports the body. Without bones, the body collapses.

The desert has its bones, too, but they are far more delicate than those that support our bodies. In many deserts, and in many other places, too, including the tundra, the skeleton is an exposed layer atop the rocks and soils and sands.

If you have ever been to southern Utah, especially to Arches and Canyonlands National Parks or the San Rafael Swell, you have seen the dark soil that covers so much of the area. That dark soil, which is actually a crust atop the desert soil, may look like the remnants of a fire, but it is in fact an organic community that, after water, anchors the living ecosystem here. This crust is known by various names-- among them are cryptobiotic crust, cryptogamic crust, biological crust, organic crust and microbiotic crust. Here, I will refer to it as the cryptobiotic crust.

Cryptobiotic crusts are actually found in most of the world, and the colors vary by region, but it is in arid regions and places where the growing season is short (like on the tundra) that the crusts are the most fragile. They feature prominently in American landscapes such as the Columbia Basin, the Great Basin, and the Sonoran Desert, but they seem most on display (because of the intensely dark color and the large concentrations of them) on the Colorado Plateau, which covers most of southern Utah and parts of northern Arizona, western Colorado, and northeastern New Mexico. In fact, it is in many of the Utah parks that signs and park newspapers inform visitors of the crusts and ask them to avoid stepping on them.

The cryptobiotic crust is a collection of mostly algae (green and brown), cyanobacteria (formerly known as blue-green algae), lichens, and mosses, though other organisms can be there as well. As time passes, the crust grows both out and up; some mature crusts can reach "heights" of about four inches (app. 10 cm)-- this is only what is above-ground.

All the organisms play a role, but the chief actors seem to be the cyanobacteria. More on their roles is detailed below, but here's some food for thought: these microscopic organisms are believed to be deserving of much of the credit for life on earth. Scientists believe that "thick mats" (from the Canyonlands page linked to in the lasts section) of cyanobacteria converted the planet's atmosphere to an oxygen-rich one from one rich in carbon dioxide. Now that's a little humbling, isn't it?

Value

So who cares? What's the big deal?

There are two main functions the cryptobiotic crust fulfills:

Stabilizing the soil-- Many of the organisms comprising the crust work on their own and together to cement the soil to themselves, making it more resistant to erosion by wind and water. That, in turn, provides a better foundation for plants to grow. Furthermore, plants growing from the crust do better than the same species growing in "regular" soil nearby; the "crust plants" tend to have more nutrients in them, grow stronger, and live longer.

It would become an exercise in plagiarism or clever paraphrasing to attempt to explain the intricate workings of the crust that make it a boon to plant life, but here is a quick account: when wet, the cyanobacteria move around and create a web-like array of fibers, which join loose bits of soil together and make it remarkably resistant to wind and water erosion. The cyanobacteria also aid in nitrogen fixation, providing a crucial crutch to plants growing in an environment that otherwise has low levels of nitrogen.

Retaining Water-- Scientists have found that the healthier, more jagged crusts allow better infiltration and retention of water than do crusts that are less pristine or less developed.

Damage and Its Effects

Aside from long-term changes in climate, the greatest threats and damage to the cryptobiotic crust come from-- this will surely be shocking-- humans or human-related activities: stepping on the crust, ORV use, and cattle grazing. It is easy to find damaged or destroyed crusts close to popular hiking trails in national parks and on public lands open to "mixed usage," a term that often means grazing, mineral extraction, and/or motorized vehicles are allowed.

Another threat is fire. Severe fires can cause significant damage to the crust. At the same time, though, soils protected by cryptobiotic crusts recover from fire more quickly than those not so protected do.

Fire is part of the natural cycle. It can be argued both strongly and well that fire should be allowed to take its course in the wilderness. Indeed, fire suppression has played a major role in some of the catastrophic wildfires of recent years.

It is harder to argue, though it can be done, that trampling by tires and feet, both human and bovine, are part of the natural cycle in the desert. The problem with the trampling is this: the crust can take decades to develop to maturity but is so fragile that it can take seconds to destroy it; some organisms can recover quickly, but others can take over a century to do so. And while it can be said that the grazing is necessary because of our food needs, it really cannot be said that the other forms of human-caused damage occur solely for the sake of a better picture or a little fun.

When the crust dies, the soil is vulnerable to invasive species and being washed away. And so can die the ecological integrity of the ecosystem. Anyone who passed basic Life Science in high school should be able to understand this. Will the whole ecosystem collapse if one patch is disturbed? No. But every little bit helps, or hurts.

Caring for the Crust

Wilderness conservation will help, of course, but since humans pose the greatest short-term threats (geologically speaking) to the crusts, it is humans that must individually choose how to act. Stay on established trails. When that is not an option, make an effort to hike through washes and on rock slabs as much as possible. My steps across the crust back in 1997 are steps I wish I could take back, but I can't do that. However, that was the last time I stepped on the crust except when I had no other choice, and those times when there was no other choice have been very few and brief; I can count them on one hand. It's understandable that a yearning for wilderness and splendor will take you from the established trails, but out in these fragile parts of the desert, it's not like bushwhacking through briars and deadfall, and we can all take a little extra care. If your route finds you having to engage in extensive crust-crunching, you might consider the bigger picture and look for a friendlier way or another destination entirely. We shouldn't pursue our fun when that means we harm what we love.

Final Words

As you can (hopefully) see, what can kill you so easily, you can kill easily as well. The difference is that nature is what it is-- sublime yet subtle, lovely yet deadly, simple yet complex, and always indifferent-- and therefore cannot be called to account for the harm it does, while we, through ignorance or malice or deed, do destroy what we cannot replace.

So breathe in the wonders and the secrets of the desert. But tread lightly. Just one step-- and that one step is never the only one since everyone taking it thinks the same thing: "What's one step, one wildflower picked, one rock collected...?"-- can have consequences. That "one little thing" may affect the fate of a world.

External Links

For more information--

Wikipedia page
Article about crusts in the Sonoran Desert
Information on crusts from Canyonlands National Park site