Category Archives: Texas

Ghosts of the Past: Stromatolites

The 1.25 billion year old Castner Formation is exposed in the Franklin Mountains near El Paso.

I believe in ghosts. They hide in plain sight, urging us to listen to the stories they have to tell.

It was my birthday and, feeling just a wee bit sorry for myself (I’m of that age), I decided to go in search of something older than I was—the stromatolites of the Castner Marble in the Franklin Mountains near El Paso. Now, these stromatolites aren’t just a little older than I am, they’re way older than I am. About 1.25 billion years older. Yes, that’s right: 1.25 billion.

Math isn’t the strongest of my academic skills, but let’s work our way through this. Let’s say you wanted to count to 1.25 billion—just to get a sense of how colossal that number is. If you keep up a steady rhythm of a number per second (and absolutely no stopping for dinner, a potty break, or Facebook), it will take you 40 years to reach 1.25 billion. If you wanted to restrict your counting to a mere 8 hour day, buckle down for 120 years. Hopefully, you don’t get confused, skip a number, and have to start all over. That would be depressing.

Tiny, single-celled cyanobacteria create layered sedimentary rocks.

So I’m in search of 1.25 billion-year-old stromatolites. In case you’re wondering, stromatolites are a type of sedimentary rock created by single-celled photosynthetic cyanobacteria (that’s blue-green algae). These microorganisms like to congregate in large groups, forming sticky mats in shallow water along a shoreline. I don’t think anyone knows why the stickiness is necessary, but the result is that the bacterial mats accumulate sediment that clogs the system up. The bacteria, being photosynthetic, need the sun’s energy to produce food, so they move upwards, forming another mat on top of the sediment. And so it goes. Layer after layer, eventually forming a cauliflower-shaped lump of rock in shallow water.

Now the amazing thing is that these single-celled cyanobacteria have been carrying on like this for over 3.2 billion years. In fact, stromatolites are some of the oldest fossils in the world. They reached their peak diversity just about the time the Castner Marble stromatolites formed. After that, they’re harder to find. The theory is that grazers evolved that found a stromatolite mat downright tasty and pretty much ate them to near-extinction.

Arizona Barrel Cactus (Ferrocactus wislizeni) have hook-shaped spines that can grab an unsuspecting ankle.

I cajole a geologist friend into going with me, and we head westward, driving past yucca-studded grasslands and mesquite-topped sand dunes. We skirt El Paso and climb the Trans-Mountain Highway through the Franklin Mountains. I navigate, reading directions from the Geological Excursions to a Transmountain Precambrian Adventure field guide that I’d downloaded from the internet. We’re looking for Stop 2—the Castner Marble Stromatolites. A gust of wind shakes our vehicle as we round the corner.

We pull over onto a wide gravel patch (obviously not the first geologists to investigate this location) and begin walking back down the highway to the end of the guardrail. Another gust of wind nearly knocks me off the mountain.

The authors of the field guide suggest that we follow a small trail down into the valley, and up the other side. The stromatolites will be there.

The trail is, indeed, narrow, and very steep. I cautiously make my way down, trying to avoid the baseball-sized round rocks that ensure a quick—and most likely painful—descent down the slope. I skirt the lechuguilla, prickly pear cactus, and a barrel cactus or two to arrive at a 2 to 3 ft thick band of light-colored rock.

A layered band of stromatolites are exposed in the hillside.

“Are you sure these are stromatolites?” I ask Blaine. He’d gotten there before I had and was poking and prodding at the rock as geologists tend to do.

“Yeah, sure. Look.” He points to the thin, wavy layers in the rock. And there, right before me is evidence of the earliest life in the Chihuahuan Desert.

With just my naked eye I can distinguish layer after layer of sediments trapped by cyanobacteria over a billion years ago. To see the actual fossils, I’d need something slightly stronger, like a microscope. Most of the layers are flat-lying to slightly wavy—an indication that the mats collected sediments in relatively calm waters.

Stromatolites aren’t flashy like a trilobite fossil or spectacular like an ammonite. But all in all, they’re probably far more important. Stromatolites hint at the origin of life. When the cyanobacteria were trapping these sediments, the skies were pink—filled with methane and ammonia and other gasses that would kill us today. The land was barren. Not a single, living thing existed out of the water. But in the water, slimy mats of green bacteria clung together, creating their own little rock. The cyanobacteria were photosynthetic, and that nifty trick of converting the sun’s energy and some carbon dioxide into food while releasing oxygen as a byproduct was changing the world. A few billion years of lilliputian, single-celled bacteria releasing minute bubbles of oxygen created an oxygen-rich atmosphere necessary for complex life to evolve. Take a deep breath. That’s you I’m talking about.

Living stromatolites are pretty rare now, but they’re still around. In Cuatro Ciénegas, a desert wetland in the Chihuahuan Desert of northeastern Mexico, stromatolites can be found in the pozas or spring-fed pools of the marsh.

Scientists working at Cuatro Ciénegas cored one of the active stromatolites. The mat consisted of a complex community of microorganisms—not just cyanobacteria. The top layer was composed of diatoms (distinctive algae with transparent cell walls), below that was photosynthetic cyanobacteria. A third layer consisted of purple sulfur bacteria. These bacteria photosynthesize using hydrogen sulfide rather than water and produce elemental sulfur as their byproduct. Below that was a sulfur-reducing bacteria that takes the elemental sulfur and reduces it to hydrogen sulfide. “Each layer obtains and processes energy in a different way and produces different waste products, and yet it is an interactive community where each layer contributes to the survival of the mat as a whole,” the scientists concluded. Stromatolites are all about being good neighbors.

Stromatolite band exposed in the Franklin Mountains near El Paso.

I poke around the rocks, distracted by rainbow cactus with fat buds, and a lizard warming itself in the sun. None of this would be possible without those little cyanobacteria that lived in an ancient sea long, long ago. I wave at Blaine, who’s wandered off to look at a contact or something geological and we head back to the car. Finding rocks that are billions of years older than I am, makes me happy—all in all, a pretty spectacular birthday.

Also posted in Chihuahuan Desert, Fossils, Geology

Places: West Texas Rest Stops

"Watch for Snakes" Warning Sign at a rest stop in west Texas

Watch for Snakes!

I’ve always thought of roadside rest stops as a necessity. You’re in, you’re out, you’re on your way. But I’m working on a photography project about the history of automobile tourism in West Texas, and I’ve started looking at rest stops in a slightly different way.

I grabbed my camera at this rest stop on I-10 between Balmorhea and Fort Stockton when I saw the “WATCH FOR SNAKES” sign. I’ve noticed warnings like this before, but they’re usually on a path leading to the picnic tables. This prominent sign made me think. Should I watch for snakes in the restroom? Given the fact that the rest stop is in the Chihuahuan Desert of West Texas, and that the restrooms have cool, tile floors, it wouldn’t surprise me at all if I found a rattlesnake curled up next to the toilet.

So I was on the lookout for snakes.


Buffalo Soldier with his horse

Buffalo Soldier Tile Mural

But I found something even more wonderful. Across the bathroom wall was this tile mural of a 19th century Buffalo Soldier and his horse. The Buffalo Soldiers were African-American infantry and cavalry troops stationed at Fort Stockton (1867-1886) and Fort Davis (1867-1885) after the Civil War. The soldiers were responsible for protecting travelers on the San Antonio-El Paso road, constructing telegraph lines, guarding watering holes, and conducting campaigns against raiding Apache and Comanche warriors.

This mural made me think. Were all of these mid-1960s rest stops decorated with murals depicting local history? I grabbed my map, checked for the next rest stop, and headed east.


A theropod dinosaur stomps across the landscape

Acrocanthosaurus Stomps Across a Cretaceous Swamp in Pecos County

The next stop was just past SH 190 (the Iraan turnoff).

Here, a salmon-pink dinosaur stomps across the wall, glittering white teeth bared. This one puzzled me at first. A dinosaur? Out here? But then I remembered a roadside park near Girvin (a few miles northwest of the rest stop) where, 120 million years ago, a theropod dinosaur squelched through the mud.  In 1965, highway workers uncovered its three-toed tracks preserved in the limestone of a creek-bed. Paleontologists decided that an Acrocanthosaurus—a genus of dinosaurs that existed in the early Cretaceous (125 mya to 110 mya) and had a distinctive short ridge along its spine—left the tracks as it foraged along the shore of an ancient sea.

Eureka! I was on to something. Like a bloodhound hot on the trail, I started looking for rest stops. The 1960s-era rest stops were not only examples of quirky, fun public art, but also related to the history of the region. I love this kind of thing.

Brands and an oil rig are depicted in the Nolan County rest stop.

Brands and Oil in Nolan County off Interstate 20

Over the next couple of days, I went on a rest-stop treasure hunt. Even my mom got involved. I’d promised her a Grand Adventure for Mother’s Day and suggested we drive the backroads of Central Texas looking at wildflowers. Instead, she remembered an old rest stop up near Fort Worth. Could we go check it out? You’ve just got to adore mothers like that. The old rest stop near Fort Worth was gone, but we discovered some other treasures.

The Nolan County rest stop (on I-20 between Sweetwater and Trent) was the most complex one that I visited on my three-day trip. Tile-work murals cover the entire bathroom. A frieze of historic brands circle the walls and against the back wall is an oil rig, quail, deer, and a variety of other wildlife.


Standoff between a cowboy and his Hereford.

Cowboy and Herefords, Nolan County

On the side wall of the Nolan County rest area the mural continues, depicting a cowboy with his Herefords. As with the other murals, there’s a story to tell. Nolan County was founded in 1876 and by 1880, there were 52 ranches in the area. Herefords, a British breed that was exceptionally suited to the Texas environment, gradually replaced Longhorns as the cattle of choice on the ranches. I wondered if the brands shown on the walls were those of the first 52 ranches, so I gave Melonnie Hicks, the Executive Director of the Pioneer City-County Museum in Sweetwater, a call. I caught her at a bad time, and she wasn’t sure about the brands. But, she told me, the museum has actual brands from those historic ranches, and anyone that’s curious can drop by the museum and take a look.

The oil rig is a nod to the discovery of oil in Nolan County in 1939 and an oil and gas industry that boomed in the 1950s.


Exhibits in rest stop on Interstate 20

The History of Auto Tourism Exhibit in Eastland County

I have to admit that I have a fondness for the old-style rest stops and their art, but I can see why the Texas Department of Transportation is replacing some of them with new, mega-safety rest areas. The old ones are small. Some are dark. People complain that there aren’t doors on them, making them potentially unsafe.

In 2001, TxDot began building a different style of rest stop. These are big, open, airy buildings with lots of parking, playgrounds, and even WIFI. But they’re more than that. To reduce the number of fatigue-caused accidents, TXDot engineers wanted people to stay longer. They worked with county historical commissions, schools, and other local groups to create rest areas that portrayed the local community. In a sense, they’re small museums, complete with interpretive panels, artifacts, and hands-on, computer-based interactive exhibits. They’re a destination on their own.

So next time you’re out for a long drive, pull off and enjoy the art and history of Texas rest stops. Which are your favorites?

Also posted in Chihuahuan Desert, Places, Travel Tagged , , , , , , |

Places: Big Bend Ranch State Park’s Arroyo Mexicano

Big Bend Ranch State Park covers 311,000 acres of the Chihuahuan Desert.

Big Bend Ranch State Park: The Other Side of Nowhere

Big Bend Ranch State Park hugs the Mexican border and sprawls over 311,000 acres of the Chihuahuan Desert in West Texas. State park staff affectionately call it “The Other Side of Nowhere.” To the casual visitor, the park appears to be all rugged mountains, deep canyons, and miles and miles of rough roads designed to destroy your vehicle and shake the fillings loose from your teeth.

But those rugged mountains and deep canyons hold treasures if you’re a naturalist. The rough roads? They’re just a necessary evil if you want to experience the park.

Groves of cottonwood and ash trees line the bottom of Charro Canyon.

Cottonwood, Ash, and Oak Trees Line the Bottom of Chorro Canyon

I spend two days with Blaine Hall and Roy Morey exploring sites for a Native Plant Society of Texas field trip. Blaine aka “Big Foot” wears one shoe 3 sizes larger than normal to accommodate the brace and bandages that stabilize an ankle broken during a hike two weeks ago. Recently retired from his position as the interpretive ranger for Big Bend Ranch State Park, Blaine chatters away, teasing Roy and me, and pointing out geologic features as he skillfully guides the truck up rock-covered slopes, across ridges of limestone, and down sandy washes. He pulls over frequently so that we can enjoy the view.

Roy is quiet, not letting Blaine’s teasing phase him. Roy is a plant person. After retirement, he moved to Terlingua and began compiling photographs of the plants of Big Bend National Park. His hobby became a full-time pursuit, ultimately resulting in Little Big Bend: Common, Uncommon, and Rare Plants of Big Bend National Park. Once he completed that book, Roy shifted west and began working on a companion volume that will describe the plants of Big Bend Ranch State Park.

“I need to get up there someday,” says Roy, looking up at the sheer cliffs of a mountain. I’m surprised. Between Roy and Blaine, I would have sworn that they’ve walked every inch of the park’s 311,000 acres.

Today, we’re looking for unusual plants, so we head for Arroyo Mexicano, a box canyon that ends at Mexicano Falls. Canyons often harbor botanical treasures such as groves of cottonwood and ash trees and tiny plants that cling to the rock walls. Canyon walls protect plants from the harsh sun and fierce winds of the desert and often have seeps and springs that provide extra moisture. “One of the only mountain laurels in the park is up Arroyo Mexicano,” says Roy. “I hope it’s still alive.” It was.

An ammonite impression in limestone.

A Dinner-Plate Sized Ammonite Fossil in the Limestone

“Want to see an ammonite?” Blaine asks as we drive down Fresno Canyon. The creek has eroded deeply into the rock, exposing the flat-lying, flaggy Cretaceous limestone of the Boquillas Formation and the nobby, white limestone of the Buda Formation.

We pile out of the truck to admire the dinner plate-sized ammonite lying exposed on an upturned piece of Boquillas limestone. The thick limestones and this ammonite fossil are evidence of a time when a shallow sea covered part of Texas. You won’t see ammonites swimming around today. The last of them went extinct when a giant meteorite struck the earth about 66 million years ago. The short and long-term effects of the meteorite impact—wildfires, tsunamis, and clouds of debris that blackened the skies and blocked the sun for years—killed about ¾ of Earth’s plants and animals.

A Mexican Buckeye Provides Nectar for Pollinators

Mexican Buckeye Tree on the Edge of the Arroyo

We eventually arrive at the mouth of Arroyo Mexicano, shoulder our packs, and trudge our way up the canyon. I’d like to say that we hiked briskly, but I have to admit that I’m a trudger in soft sand. Fairly quickly, we see pools of water and a shallow stream meandering its way across the sand bottom. Groves of cottonwoods, their new leaves a beautiful, fresh spring green, provide shade along the way.

Occasionally a spot of pink reveals the location of a Mexican buckeye tree. These early-blooming shrubby trees are an important source of nectar for bees and butterflies. A Mournful Duskywing flits between flowers, ignored by a nectaring Grey Hairstreak. I search unsuccessfully for a Henry’s Elfin—a small brown and silver butterfly that uses Mexican buckeyes as a host plant. Henry’s Elfins are more common in the eastern United States, so seeing one in West Texas is pretty special. Roy and Blaine have moved on, so I quit looking for butterflies and hurry to catch up.

Huge velvet ash trees with their gnarly roots exposed.

Velvet Ash Trees in the Arroyo

As we move up the canyon, we walk under large velvet ash (Fraxinus velutina) trees. I am fascinated by the texture of the bark and the thick, gnarly roots wrapped around giant boulders. Of course, the exposed roots are also a warning sign. This canyon carries water—often with enough force to roll boulders and wash away enough sediment to expose the roots of trees. I check out the sky (gray clouds gathering) and look for high ground. The vertical walls of the canyon look back. I’m doomed.

Conglomerate boulder made of smaller, rounded, igneous rocks.

Volkswagen-sized Conglomerate Boulder in the Arroyo

In places, we skirt boulders the size of Volkswagon Beetles or larger. I envy Blaine his ability to read these rocks. “See,” he says, “this rock is made up of older rocks that have been cemented together to form a conglomerate.” This particular conglomerate is just a baby rock if you can wrap your mind around geologic time.

All of the “clasts” or smaller rocks that make up the conglomerate are volcanic in origin which means they were deposited about 27 million years ago. Over time, they broke away from their parent rock, were tumbled and smoothed, and came to rest in one place long enough for the white matrix rock to cement them all together again. The conglomerate eventually broke up, and Volkswagon-sized boulders tumbled down the slope, coming to rest in the stream bed.

Fern-covered walls and plunge pool of Mexicano Falls

Mexicano Falls at the End of the Arroyo

After about 3.5 hours of walking and stopping to admire rocks, plants, and scenic views we reach the end of the canyon. At this time of year, Mexicano Falls is more of a drip than a fall. Maidenhair ferns, yellow-flowered columbines, and thick carpets of moss fill the cracks where water seeps from the rocks. The plunge pool is thick with green algae.

Blaine points to a gap in the canyon rim where water funnels through to create a waterfall during the summer rainy season. I’d love to be there to see the waterfall, but then I remember those exposed roots and the flood debris wrapped three to four feet high up the trunks of the trees that we were walking through earlier. Flash floods are real and dangerous in this canyon.

The tiny, yellow, fringed monkeyflower hangs from the wet walls of the canyon.

Fringed Monkeyflower Hangs from the Wet Walls of the Canyon

While Blaine and I photograph the ferns and columbines, Roy walks the face, scouring the seeps for fringed monkeyflower (Mimulus dentilobus). “Found it!” he calls. Fringed monkeyflower is a rare plant in Texas, found only in places where water drips from the West Texas mountains. I’m surprised by how tiny it is. The bright yellow flower with its fringed petals and red spots in its throat rises above a mat of small leaves hugging the wet rock face. We’re lucky to find these in bloom. It’s only March and according to the field guides, fringed monkeyflower blooms from June to August.

Blaine and Roy fix a flat tire.

Flat Tire

The wind begins to blow, and the clouds build, getting thicker and grayer. We decide to return to the truck before a storm drenches us. The hike back takes about 2.5 hours. We quickly pack up and drive off, but Blaine stops almost immediately. He walks around the truck and discovers a flat tire. “That’s two this week,” he mutters. Razor-sharp rocks can slice through the sidewalls of a tire and mesquite thorns pierce treads easily. We unload all the gear to access the spare, and Blaine and Roy begin the laborious task of changing the tire. Fortunately, nothing goes wrong and within 30 minutes we’re back on the road. We eliminate a couple of side trips and head straight back to the park headquarters at Sauceda. Driving any further than necessary without a spare is foolish.

The flatirons of the Solitario provide a perfect backdrop for a patch of Big Bend Bluebonnets.

Big Bend Bluebonnets and the Solitario

Since Blaine and Roy have the flat-tire situation in control (and they’re a bit annoyed with my photographic documentation of the event), I wander off a few feet to photograph a patch of Big Bend bluebonnets with the flatirons of the Solitario in the background. The Solitario is a massive igneous dome created when molten rock pushed up the flat-lying rocks above it creating a circular feature 10 miles in diameter. The dome attracts geologists, botanists, and naturalists from around the world and is probably the most famous feature in Big Bend Ranch State Park.

I love going to the Solitario, but this opportunity to explore Arroyo Mexicano with Blaine and Roy was as close to perfect as a day could be.

Also posted in Chihuahuan Desert, Geology, Plants Tagged , , , |

Ghosts of the Past: Mexican Grey Wolf

Mexican Grey Wolf in the El Paso Zoo, Texas.


I believe in ghosts. They hide in plain sight, urging us to listen to the stories they have to tell.

Ash, a Mexican Grey Wolf paces in her enclosure at the El Paso Zoo. She circles through the shrubs, down a slope and back around the rock-lined pond. She pauses for a few seconds to stare at me and then continues her pacing. Ash may not know it, but she’s one of the last of her kind.

Mexican grey wolves such as Ash and her companion, Ivy, were once common throughout the mountain woodlands of central Mexico,  Arizona, southern New Mexico, and southwestern Texas. Vernon Bailey, in his Biological Survey of Texas (1905) describes the grey wolf as “still common over most of the plains and mountain country of western Texas.” But even in the early 1900s, grey wolves were being hunted by ranchers and professional wolf hunters. Bounties were high and wolf hunting was a profitable business. “There is a strong temptation,” says Bailey, “for the hunters to save the breeding females and dig out the young each year for the bounty, thus making their business not only profitable but permanent.”

Not quite permanent, though. In 1972, Dr. James Scudday published a brief report in the Journal of Mammalogy about two young wolves that were trapped in Brewster County in December, 1970. These were the last grey wolves seen in west Texas and pretty much the last seen in the southwest north of the border.

The Mexican grey wolf was put on the endangered species list in 1976 and captive-bred wolves—descendants of breeding stock captured in Mexico—were used to reintroduce the species to the wild in the Blue Range Wolf Recovery Area of New Mexico in 1998. The recovery program has proceeded in fits and starts. Reintroduction of a predator such as the grey wolf has not been enthusiastically embraced by rural and ranching communities, making it an often contentious political, rather than ecological, issue.

Jason Mark, takes a look at both sides of the issue in his fascinating essay Can Wolves Bring Back Wilderness (Scientific American, Oct. 9, 2015).

“Can we find a way to live with the wolf’s wildness and share space together?” questions Mark. “Can we coexist, and come to see another carnivore as something of an equal, and not just an enemy? Or do we have to control it, and in that control limit its wildness, the very thing that draws us to it?”

Will the Mexican grey wolf always be shimmering and barely visible–a ghost from our ecological past?



Also posted in Animals, Chihuahuan Desert Tagged , , , |