Shameless Promotion

Friday, February 24, the Big Bend Ranch State Park begins the first in a series of camping/photography tours that take you to some of the most rugged, remote, and scenic locations in the park. These locations are only accessible via primitive roads that are impassible to all but 4-wheel drive, high-clearance vehicles.

View from Guale Mesa Campsite

The tours are intended for photographers who would like to work in the park but who lack the proper vehicles for reaching the best sites. I will be available to answer technical questions and provide help where needed, but there are no classroom activities – just two days of uninterrupted photography.

This month’s tour is to Guale Mesa. You’ll camp atop a high bluff that overlooks Rancherias canyon on the east, La Guitarra Mountain to the south, and the Lower Guale Mesa to the southwest. A short side trip on Sunday morning will give you an opportunity to photograph scenic Tapado Canyon at sunrise. The view southwest from the canyon rim stretches all the way to the Sierra Ricca mountains in Mexico. Blue-green walls line the canyon walls to the northwest, and the rim itself is quintessential Chihuahuan Desert. Few people have even seen this magnificent sight, much less photographed it!

View of Tapado Canyon

Price for the tour is $350; it includes one night’s lodging at the Bunkhouse, one night’s camping “on location,” all meals and transportation. The tour is limited to 6 photographers – the perfect size for a campfire supper and friendly conversation. You can make reservations by calling 432-358-4444. This price will have to be pre-paid.

Note: you must bring your own camping supplies, i.e. tent, cot, sleeping bag, pillow. We are only providing the ride to the location, food, and the atmosphere.

Another Note: I’m not being paid for this; it’s all voluntary. I’m just trying to help the park. If you know anybody who might be interested, please let them know. Thank you!

Fluffgrass

One of the most common questions people ask me about plants in the Big Bend Ranch State Park regards a small grass known as Fluffgrass. Their curiosity is understandable; over 20 years ago, when I was hiking in the park for the first time, a cold front bringing freezing temperatures and on-and-off rain passed. I wasn’t well prepared for this kind of weather so I was pretty cold. When I passed Cerro La Guitarra, without my glasses, I honestly thought there were patches of snow on the ground! This image, taken from a badly faded and color-shifted negative, records the scene.

Fluffgrass on Guale Mesa

A closer inspection revealed that the white spots were a plant, but I had no idea what it was. Today I know it as Dasyochloa pulchella, the only species in the Dasyochloa genus. It is a perennial bunchgrass that forms small tufts just a few centimeters high with clumps of short, sharp-pointed leaves. Nobody seems to know much about it, or care much for it, but it is one of the most commonly occurring grasses in the Southwest.

This grass is readily noticeable, particularly when the sun is low and behind it, for it fairly glows, easily outshining everything else around. When fluffgrass drops its seeds, the translucent bracts remain on the plant, catching the light and giving the appearance of glowing.

Glowing Fluffgrass

The grass is regularly described as having “poor forage value.” When young and actively growing the plants are covered with a bluish-white down that may be objectionable to grazing animals. Later, when the plants mature, the leaves become harsh, wiry and sharp pointed. Livestock and wildlife generally avoid it; if you see it browsed, you know that times are hard.

What the animals don’t eat we can nonetheless enjoy, for this little grass is attractive at nearly every stage in its life cycle. It is particularly pretty when young for its bluish-green foliage is covered with a soft cottony down.

Young Fluffgrass Plant (Image ©Phillip Ruttenbur )

The nature of the down is not known – some experts claim it is composed of excreted mineral salts. Others say that it is made of carbohydrates. Whatever its composition, the “wool” is soluble in water and washes away with the first rain. Sometimes the down appears to be made of distinct fibers. At other times, the material looks much more amorphous.

Amorphous Looking Fluffgrass Fuzz

The nature of the wool is not known – some experts claim it is composed of excreted mineral salts. Others say that it is made of carbohydrates. Whatever its composition, the wool is soluble and washes away with the first rain.

As fluffgrass matures, it loses its bluish cast and becomes a bright green.

Maturing Fluffgrass Plant

The inflorescence is one or two centimeters long and bears spikelets which are pale in color, sometimes striped with red, purple, or green. They are rather flattened and look a bit like small fans.

Fluffgrass Inflorescence

For me, fluffgrass has become one of the Chihuahuan Desert’s many little pleasures. The plant’s constantly varying appearance, bright glow in the winter, and preference for open areas where nothing else grows, makes it a welcome sight. Its ubiquitous presence is a constant reminder of life’s resilience, even in the most difficult of environments. Look for it the next time you hike in the Trans-Pecos. It’s worth your attention.

The Beautiful Texas Madrone

Madrone on the Pinnacle Trail. Big Bend National Park

With Fall approaching, one of Texas’ most beautiful trees, the Texas Madrone reaches the height of its beauty as it puts forth its crop of beautiful red berries, often growing in hand-sized bunches and completely covering the tree. These lovely berries give the tree it’s first scientific name, “Arbutus,” which is a Latin word meaning “Strawberry Tree.” The name Madrone comes from the Spanish word madroño which means the same thing. In the winter, the combination of green, white, and red wood, bright green leaves, and large red berries makes this tree a joy to behold.

In the spring, the tree is covered with large bunches of urn-shaped, cream-colored flowers which fill the air with an exquisite fragrance.

Bunches of Tiny Urn-Shaped Blossoms

Small groups and individual trees can be found in many places. For West Texans, the best place to see them is in the Chisos Mountains and the Guadalupe Mountains.

You can see many Madrones along the road to the Basin, but without doubt, the best place to find them is in the Guadalupe’s. There are surviving Madrones on the trail leading almost due north from the Pine Springs campground. These Madrones are atypical in that they grow mostly in isolation, giving this trail a distinctly “savannah” look and feel.

The Devil’s Den trail passes through stands of this tree, and is a beautiful visit any time of the year. But the very “best of the best” location is McKitrick Canyon.

Madrones Line the Trail in McKittrick's Canyon

In the shelter of this canyon, starting in early fall, the Maples begin to change color and Madrones line the trail with their fruit-laden branches. A fall hike through this canyon is an experience you will never forget. Trust me on this.

Madrone Growing in McKittrick Canyon

The Texas Madrone is not normally a large tree – it reaches 20 to 30 feet at the most. Madrones are usually multi-trunked with tortuously-shaped limbs that are smooth to the touch. The limbs spread out to give the tree a canopy of dark, leathery leaves that stay green year round. In the spring to mid-summer blooming season, the tree produces large clusters of creamy white, bell-shaped blossoms that fill the area with a delicious fragrance.

Madrone in Bloom

The velvety-smooth wood changes appearance throughout the year. In the spring it usually runs from white to a pale green though it may sometimes be a light burgundy.

The bark often feels like skin -- soft and smooth to the touch

As the year progresses, the old bark darkens into shades of brown and red and begins to peel off. As it falls away, it reveals the younger wood underneath which may be any color between white and bright red.

The Peeling Bark is Often a Brilliant Red

In fall, the tree puts out its crop of berries.

The Sweet Red Berries Look Like Small Strawberries

In the winter, the combination of green, white, and red wood, bright green leaves, and large red berries makes this tree a joy to behold.

Mature Madrone With Fruit

Despite the Madrone’s great beauty, it is seldom seen by the general public. There are several reasons for this.

• The Madrone is a fairly rare tree in North America, growing only on the Edwards Plateau, in far West Texas, and in southeastern New Mexico.
• Its’ preference for montane habitats keeps it out of the view of the general public though hikers and backpackers are usually familiar with it.
• It is not very good at reproduction. The seedlings are palatable to deer so few seedlings survive to grow to maturity.
• It is extremely slow growing – it can take over a century for a Madrone to fully attain an adult height of 20 to 30 feet.

These factors, combined with declining habitat, rising temperatures, and decreasing rainfall are causing Madrone populations to decline.

It is fortunate that this tree is little used for utilitarian purposes. Native Americans considered the tree sacred and refused to burn it despite the excellent fire it provides. The wood is reddish-brown, hard, heavy, and close-grained. It is dimensionally stable, easily worked and it takes a fine polish; however, it is brittle and not very durable. In most of its historical applications, Madrone wood has been replaced by cheaper synthetic materials.

Madrones are more plentiful in Mexico than here, and they are used somewhat more. Leaves and bark are used as astringents and diuretics, bark and roots are used to make organic dyes, and the wood is sometimes used to make stirrups.

The berries are used most. Birds such as trogons, jays, and band-tailed pigeons eat them – Black Bears are quite fond of them.

The Main Trunk Shows the Scars Left by Foraging Bears

If you hike in the Chisos you will see many madrones that carry deep scratch marks from the claws of bears climbing to get the fruit. Though the fruit tastes rather bland to modern palettes, it can be made into jellies and jams. The Tarahumara Indians of northern Mexico make an alcoholic beverage from fermented Madrone berries and flavor tortillas with the tree’s flowers.

One would think that any tree this beautiful would be avidly cultivated, but that is not the case. Texas Madrones are notoriously difficult to plant and grow. Twenty years ago it was widely believed that it was impossible to grow one from seed, or to transplant one from the wild. In 1975, the Texas Horticulturalist magazine reported on an experiment that was conducted to try to germinate madrone seeds. Of the 10,000 seeds planted, researchers succeeded in germinating only 2 seeds.

In the past 20 to 30 years, growers have gotten better, and today a handful of nurseries, mostly in the Kerrville area, have mastered the business; fair-sized Madrones may now be purchased for home gardens.

We now know enough about this tree’s needs that amateur gardeners can reasonably expect to be able to grow them. Should you decide to try, here are a few facts you should keep in mind.

Seeds need to be planted shortly after harvesting. If they remain moist, germination can begin within 7 to 14 days. Once dried they rapidly lose fertility. After only 6 months of cold dry storage you can expect fewer than 40% of seeds to be fertile. After 2 years fertility drops to around 4%.

Seedlings grow best with a 12-hour photoperiod at daytime temperatures of 81 degrees and nighttime temperatures of 64 degrees. The soil should be well drained and run close to a neutral pH (6.8 to 7.2).

Good growth occurs at 60 to 70 percent relative humidity at a light intensity of 6,500 to 10,000 lux.  At higher light intensities, growth may be reduced by photo-bleaching of chlorophyll, though high soil moisture may ameliorate this problem. Under ideal conditions you can expect germination rates of from 20% to 90%.

Madrones have a poorly developed fine root system and what they have is easily damaged. Worse, even slight damage to the root system is usually fatal to the tree. Growers should take every precaution to avoid root stress – this is not one of those trees you can take home, rip off the plastic bag, fluff up the roots and toss into a nice-sized hole. Rather, bags should be removed with the utmost care, the tree lowered into a hole of exactly the size of the root ball, and additional soil gently sifted over to fill the hole (no tamping please). Home growers may benefit from starting young trees in biodegradable containers that can be lowered into planting position without disturbing the tree’s roots.

Much remains to be learned about this fascinating tree, but its best hope for survival probably now lies with home horticulturalists who take the time to learn how to grow it, and who share their knowledge with others – without our help it is unlikely that this tree will continue to do well here in the northern Chihuahuan desert.

Plant Adaptations to Desert Conditions

The Chihuahuan Desert is the most thickly vegetated desert in North America. Indeed, if you visit in during the rainy season you might wonder why it is called a desert at all.

It hardly looks like a desert at all during the rainy season.

Though for the most of the year the Chihuahuan Desert is not green, even in the most arid, empty spaces hikers must watch their footing carefully for most desert vegetation is well armed and intimate encounters are best avoided.

In dry periods the land is brown and most of the plants look dead. But these plants aren’t suffering. They’re not “struggling to survive.” They’re just doing what desert plants do – quietly waiting for the next rain.

The vegetation here is dried out, but still quite alive

Desert plants have developed a number of strategies for living with the protracted dry periods and seasonally high temperatures that characterize the Chihuahuan Desert. Some approaches are shared by most desert plants – others are more specialized. Among specialized adaptations, most plants have followed one of three different paths to success: succulence, tolerance, and evasion.

Cacti swell almost to bursting when water is abundant

Succulent plants are water hoarders. They store water in stems, roots, or fleshy leaves in special structures that are good at retaining moisture. All cacti are succulents, but many non-cacti desert plants use the same adaptation. Succulents include agaves, aloes, and many euphorbias. Aside from storing water in their tissues, succulents have use other specializations to succeed.

Succulents must absorb large quantities of water in short periods of time, but they cannot absorb water from soil that is not wetter than their own interiors. Since desert soils are rarely and only briefly wetter than the interiors of any plant, nearly all succulents have extensive, shallow root systems. These shallow roots come to life quickly at the slightest sign of rain, and they harvest water from the soil rapidly and efficiently. Most succulents have roots less than 4 inches below the surface with feeder roots that lie within half an inch of the surface. They spread out far from the mother plant – for example a two-foot-tall cholla may have roots over thirty feet long!

A succulent such as a cactus looks very much like a bag of water to most thirsty animals, so succulents guard their water fiercely. Most are spiny, bitter, or toxic, and often all three. A few unarmed, non-toxic species exist, but they are usually confined to extremely inaccessible locations such as vertical cliffs or within the canopies of other spiny plants. The plant’s water is usually bound in extracellular musilages and inulins (soluable fibers) that release water only reluctantly, so even if part of the plant breaks off, it stays moist inside for a long time. Waxy cuticles make them practically waterproof when their stomata are closed; those that have leaves shed them quickly when the soil dries out.

Many succulents also employ a special type of photosynthesis known as CAM for Crassulacean Acid Metabolism. Instead of synthesizing carbohydrates, they synthesize Crassulacean acid during the day while their stomata are closed and store it in their tissues. At night, when temperatures are lower and humidity higher, they open their stomata and break down the acids into carbohydrates using carbon dioxide from the air. CAM is extremely efficient at using water. Plants that use it consume only about 10% of the water other plants consume to synthesize the same amount of carbohydrates. The overall rate of photosynthesis is slower however, so CAM succulents are usually slow-growing.

CAM photosynthesis often gives the plant a reddish color

CAM plants are able to “hybernate” during dry times, recycling oxygen and carbon dioxide to conduct very low-level photosynthesis. Since they have not gone completely dormant, CAM plants can resume growth within 24 to 48 hours after a rain. An agave can sprout new roots within 5 hours of a rain, whereas dormant shrubs usually take two weeks or more to revive.

Just after a rain, this fern is partly hydrated, partly dormant

Instead of storing water, some plants simply dry out, lose their leaves, and appear to be dead. In this condition, drought-tolerant plants reduce their metabolisms to near zero when it is dry, but they are ready to resume growth as soon as the rains arrive. Some shrubs can become dry enough to use for kindling, yet they are alive. They often shed leaves during dry spells, and those that keep them usually have resinous or waxy coatings that retard water loss. Desert ferns can become completely dehydrated without dying.

Drought-tolerant plants usually have more extensive root systems than their water-loving relatives, with roots extending to 2 or 3 times the size of the canopy. In addition to breadth, many grow very deep roots to reach moister levels of soil. These deeper roots can sustain growth for many weeks after a rain.

Because drought-tolerant plants rely more on deeply buried moisture, they take longer to revive than succulents. In creosote bushes, traces of green may appear early after a rain but fully active new root systems and new leaves usually take 2 or more weeks to develop.

Desert Marigolds may wait out a drought as seeds

Some plants simply evade drought. These plants die during dry periods, and rely on seeds germinating during future rains to preserve the species. In terms of species count, drought-evasive plants are the most successful adapters to desert climates. Seeds have almost no metabolism and possess great resistance to environmental extremes. Seeds appear to be remarkably “intelligent.” Most will only sprout under very specific circumstances such as a minimum amount of rain, a particular season, a temperature window, specific soil types and conditions and frequently some combination of the above. Even under the best of circumstances, not all seeds will germinate, for some remain dormant. Some bluebonnet seeds, for example, will not sprout until they have been in the ground 10 years. How seeds manage these remarkable feats is not clearly understood.

Some plants are adapted in several ways. Ocotillo, for example, uses CAM metabolism and a broad, shallow root system like succulents. But it drops its leaves and dries out like a drought-tolerant deciduous shrub. Semi-succulent yuccas store some water in their leaves but also put down deep roots to obtain most of their water.

Aridity affects many conditions important for plant survival. The clear dry air allows unfiltered sunshine from dawn to dusk. The solar radiation produces very high temperatures which are lethal to non-adapted plants. On the other hand, the dry air loses heat quickly at night allowing the temperature to drop dramatically.

Schott's Acacia has very small leaves

Nearly all leafy desert plants sport small leaves. At first it would seem that small leaves would not be useful. After all, they have a much higher surface-to-volume ratio than bigger leaves and so should lose water more rapidly. But this adaptation avoids overheating, and thus, water loss. Large leaves require transpiration through open stomata to keep cool – this is not an option during the hot months in the desert. Gardeners know that tomatoes must be shaded in desert environments or they will burn. They cannot evaporate water fast enough to keep cool. But small leaves can stay below lethal tissue temperatures of about 115 degrees on a calm day with stomata closed.

Honey Mesquite remaining green during a dry period

Finally, there are some desert plants that are not really adapted to dryness at all. They survive by growing long roots that remain in the water table at all times. The mesquite is an example of such a plant. Some sources say that Mesquite roots can descend to 200 feet, others say not so deep. The average is close to 40 feet – mesquites will die if the soil dries to this depth.

The Chihuahuan Desert is uniquely endowed with a rich variety of plant life, and the phases of their lives are easily observed. Watching plant life adjust to the seasons here can be one of the unique pleasures of living here in West Texas.

A Natural Garden of Desert Plants

Lichen

Lichens must surely be one of the most unusual organisms on the planet for they are not really a true species but a community of two or three completely unrelated organisms living in the same skin. The organisms living together are symbiotic with one another – that is, none can live without the other.

The dominant partner is a fungus. Because fungi cannot make their own food, they usually live as decomposers or parasites. But in lichens, fungi maintain symbiotic relationships with other species that can make food. The symbiont partners make food by photosynthesis; they are usually an algae, a cyanobacteria, or both. Up to 18,000 species of fungi have been “lichenized” and about 40 genera of algae and cyanobacteria are found in lichen partnerships.

Several different-colored species of lichen living as neighbors

Lichen primarily reproduce vegetatively, so most lichens start life complete with all their parts. Any lichenized fungus born without its symbionts will die unless it can acquire them in some other way. Not just any symbiont will do – a lichenized fungus can live with only one species of algae or bacteria; the reverse is also true.

Fungal partners tend their symbionts by providing them with a protected environment, organizing them into patterns that permit optimum photosynthesis, and exchanging metabolites with them to improve their nutrition. They harvest their crops by secreting chemicals that cause the algae to “leak” nutrients to the surrounding tissue or grow minute tendrils that pierce the symbionts’ walls to extract food. The harvest is pretty good. Up to 80% of the photosynthesized carbohydrates go to the fungus. If cyanobacteria are present, the fungus extracts nitrogen and other biologically useful compounds it could obtain in no other way.

Lichens have been around for at least 600 million years. Their hardiness is legendary. They can live in the Arctic tundra and in the intense heat of Death Valley. They can dry out completely without being harmed, and are practically immune to ultraviolet radiation. In 2005 the European Space Agency carried lichen into outer space and left them outside the spacecraft for over two weeks. When returned to earth and watered, the lichen resumed photo­synthesis as if nothing had ever happened.

Lichen colonies can be quite large and can quite literally change the appearance of the landscape. In this photo, lichen have almost completely masked the red color of the rocks with their own bluish-grey tint.

Lichen have almost completely obscured the rock's red color with their own blue-grey tint

Both wildlife and people eat lichen. Mule deer have a taste for them; their foraging often creates a visible browse line on tree trunks. The Japanese use lichen in many traditional foods, and hikers sometimes eat them as survival food. Many lichen turn up in commercial products such as ointments, deodorants, tonics, and expectorants. One chemical which is derived from lichen, is the active ingredient in litmus paper. It changes color according to pH. Home swimming pool owners around the world use litmus paper, made with lichen extracts, to monitor the condition of their pool water.

Over 50 species of birds, including many hummingbirds, use lichen in their nest building. The female Anna’s Hummingbird covers the outside of her nest with lichen to camouflage its presence. A few insects also use lichen for camouflage. And, of course, moths and butterflies have evolved to mimic the colors and patterns of lichen to camouflage themselves. The military has noticed the patterns and colors and realized that the appearance of lichen changes very little through the seasons. A new, patented, camouflage pattern is now being used. It is claimed that this camouflage is exceptionally difficult to detect.

Lichen even play a significant role in geological processes. They produce acids which dissolve rock and help break it down. Some lichen attach themselves to rock by sinking root-like tendrils into the rock. These tendrils regularly grow as much as 8 inches beneath the surface. As they swell and contract, they create fissures in the stone. Water flows into these fissures, hastening the erosional process.

Lichens grow in roughly four shapes –

Folios Lichen

Folios lichens are flat, leaf-like organisms. You are most likely to notice them growing on tree limbs or trunks after a rain because the edges tend to curl up then and reveal the “leafy” structure.

Crustose lichens grow like crusts on the surface or between the crystals of volcanic rocks, or buried in tree bark. The brilliant red, yellow, and orange lichen you see growing in the Davis Mountains are mostly crustose lichens.

These crustos lichens grow in mineral-rich cracks on the rock's surface

These fruticose lichens look like a miniature rain forest

Fruticose lichens look like miniature shrubs. They often resemble masses of string hanging from trees or other plants.

This Squamulose lichen grows on the ground

Squamulose lichens are scaly and are usually comprised of numerous small rounded circles. Our “ground lichens” are of this type. On loose soil they sometimes appear to be growing on tiny mesas or pedestals. These elevated patches result when rain washes soil away everywhere except under the lichen.

Some lichen have such pronounced antibiotic properties that they are commercially valuable. Lichens from the genus Usnea are used in ointments and other products sold as aids to healing wounds. Lichens may be found in deodorants, laxatives, and expectorants. Ongoing research is beginning to indicate that some lichens may be useful against certain cancers and viral infections.

Lichens are one of the many “little things” that make exploring the Chihuahuan Desert interesting and rewarding.

A Small Patch of Color in the Chihuahuan Desert

The Beauty of the Chihuahuan Desert

This week I celebrated my first anniversary as a volunteer at the Big Bend Ranch State Park. I’ve never done anything more satisfying or lived anywhere I liked better. I’ve found everything I expected to find here and have harvested more than I could ever have imagined.

Tapado Canyon in the Early 90s

I’ve loved this park since the first time I saw it over 20 years ago. I came to hike the Rancheria trail. I left determined to come back and spend some serious time here. In my naieveté I believed that I could see most of the park in a year. Now I know that even a casual viewing will take much longer than that.

People sometimes ask me “why here?” In West Texas we have nothing like a Grand Canyon, no forests of giant cacti like the Saguaros, no massive snow-capped mountains, no limitless dunes, no vast areas of red rock, or wind-carved canyons – none of the icons that form the average American’s mental images of deserts.

My answer is that our desert is unique and that loving it is not difficult. The traditionally compelling attractions of space, silence, and solitude are here in abundance. Wearied spirits and frazzled nerves are quickly healed in the silence of this place. I have spent days simply listening to the sounds of wind as it rushes through draws, ravines and canyons; the rumbles, howls and whistles of the wind intermingle in a constantly-shifting tapestry of desert music. If you sit very still on a hot windless day, the silence is absolute; soon the sounds of blood flowing through your veins, air traveling in and out of your lungs, and joints and bones shifting as your body maintains its balance become the loudest noises in your universe.

Fresno Canyon is Pure Gold at Sunset

You can travel for weeks here and never see a comtrail. The absence of this industrial graffiti makes the sky, once again, a joy to photograph. Gentle pastel sunrises, blazing sunsets, or clear twilights still carry their full visual force in the Big Bend region, and our photographs are the better for it. Smoke and haze are often present, but even they can exhibit a strange beauty that somehow doesn’t seem “civilized.”

Smoke from Nearby Wildfires Make Colorful Skies

Sleeping in the open here is an incomparable joy – our clear air reveals the sky as a black velvet sphere thick with glittering stars. Though it is no longer possible to see the Milky Way in most parts of the country, here it is thick and creamy and spreads across the sky from horizon to horizon. As the heavens wheel about the North Star, outdoor sleepers become aware of the turning from brief glimpses seen during moments of wakefulness. The sky’s changing composition becomes solidly linked with the seasons in the outdoor sleeper’s experience.

During our cold clear winters and extended dry periods creosote withdraws nutrients and protective chemicals from its leaves and turns to a coppery orange color. Many bluestem grasses do the same. Other grasses assume golden straw colors; fluff grass grows in white balls that glow in the backlit sun; the Chihuahuan Desert’s dry-weather palette is the perfect complement for the warm light of sunrises and sunsets.

The Winter Palette is Warm and Inviting

Blooming Shrubs Make a Colorful Display During the Rainy Season

The Chihuahuan Desert has the most abundant plant life of any desert on the continent. The timing of our rains keeps the average soil temperature down and allows many species to survive here that otherwise could not. During the rainy season the Chihuahuan Desert gets greener than any other. Shrubs cover themselves with flowers, Ocotillos become wrapped in leaves, and wildflowers rush to grow, flower, and seed before the moisture disappears. The transformation is all the more remarkable for the speed with which it is accomplished. An Ocotillo can become fully leaved in a few days. In a week the world can be transformed.

The Desert Sparkles After a Rain

The climate’s harshness is legendary and the possibility of death is never far removed. Here you learn to watch where you put your feet and hands, observe the ground carefully when walking, and obey all the rules of heat and water. You learn to let other people know where you’re going and when you’re returning. You carry equipment for emergencies and you do all you can to make yourself visible and easy to find. And after awhile none of this is disturbing – it all becomes part of the pattern of desert living, like rising early to work in the morning’s cool air, napping through hot afternoons, and returning to activity in the evenings.

When I came here I thought I was the luckiest man alive. I still do.

Sunrise Over Leyva Creek

Desert Varnish

You see Desert Varnish almost anywhere you go in the deserts of the Southwest. But its development is not limited to the our region. It is found in El Azizia, the hottest desert on earth, where temperatures reach as high as 136 degrees and in the dry valleys of Antarctica, the coldest desert, where temperatures hover as low as -128. In the American Southwest it is a major component of paleolithic rock-art.

Desert varnish forms in arid and semi-arid regions as a film coating made of alternating layers of materials, each with different compositions. Some of these layers are rich in windblown clays and dust-sized particles, while others are rich in iron and manganese oxides and hydroxides. Usually we find smaller amounts of various metals, organic molecules, and bacteria.

The “varnish” grows, or is deposited, as a sort of patina on the surface of the rock. It’s growth is unimaginably slow – from 1 to 40 millionths of a millimeter for every thousand years. It is the slowest known accumulating, sedimentary deposit on earth.

Despite its widespread presence, and over a century of scientific investigation, we know little more than what’s in it, but we don’t really know how it happens. Mineralogists and other rock-types tend to favor the idea that desert varnish is an accumulation of dust and other materials held together by compounds that readily form on rocks as a result of weathering and other forces. But the fact that desert varnish always contains microbes, or their remains, encourages biologists to believe that the microbes create the coating from dust and minerals they capture from the atmosphere.

Desert Varnish is Usually Black and Shiny, like this patch

All of the single-agent theories have significant problems. The abiotic theories cannot account for the consistent element content of desert varnishes regardless of location. The biotic theorists, on the other hand, cannot prove a causal connection between the bacteria and the coating.

Lately we are considering the possibility that both biological and chemical processes are at work. In this hypothesis bacteria sequesters the manganese, iron, phosphate, carbonates and other materials that seem always to be present. The dust and clay form an adhesive layer which sticks everything to the underlying rock. And the layers themselves may be held together with silica and byproducts of dead bacteria. It’s an attractive idea, but we’re still not sure.

Regardless of how it is formed, desert varnish is extremely durable and fade resistant which makes it an ideal material on which to create rock-art. And our ancient ancestors did just that. Their work can be found throughout the Trans-Pecos. Many painted on rocks using natural pigments. Others scraped or chipped the desert varnish off, leaving the lighter underlying color to form the drawing.

Typical Rock Shelter Containing Prehistoric Art

Here in the Trans-Pecos we have a rock-art tradition that represents the work of a single cultural group of Indians over an extended period of time. The paintings show the beginning, a slow refining of style, and the dying of a tradition that was completely isolated from outside artistic influences.

Though it is durable, Desert Varnish is not indestructible. Vandalism and natural weathering of the rock are the most common causes of rock-art deterioration. Weathering can loosen the underlying rock and dislodge the varnish. Many sites have been destroyed in natural landslides. Graffiti obscures the underlying figures and unfortunately, the materials used by vandals often damage the underlying art beyond repair.

Weathering Loosened Some of the Underlying Rock Leaving Patches of Desert Varnish