Chapter III: Part 3: Guide and Adviser 110 (2)

Each annual and perennial species has its own preferred blooming season and favored locale. The long-legged Big Bend bluebonnet may start flowering in December and keep on blooming until June. Sometimes this rangy relative of the Texas bluebonnet will bloom in such masses that the lowlands look like they have been painted blue. The daisy-shaped nicollet also likes gravelly soils, while the desert verbena does best in disturbed areas. This lavender-pink sweet william, a spring bloomer in the lowlands, appears later at higher elevations as springtime ascends the mountains. As a rule the spring bloom peaks in the lowlands in April, and species that prefer higher elevations flower a little later. Thus the bracted paintbrush begins to flaunt its red flags in June grasslands, and beautiful, deep blue tube-flowers may be seen from May to July on snapdragon vines in the Chisos woodlands. Usually the luxuriance of the spring bloom will depend on the amount of rain that fell during the preceding fall and winter, and the months of June and July are apt to show few flowers at lower, drier elevations. But with summer rains in August and September, many springtime flowers bloom again, sometimes more spectacularly. These rains also produce a bright first flowering from such summer and fall species as the low-lying, sweet-smelling limoncillo, and the broomweed that gold-plates Basin hillsides right through October and November.

Flowers

Many insects pass the dry months as the seeds do, lying dormant in eggs or cocoons. The same life-giving rains that waken the seeds quicken the insects. And as the flowers come into their own there is a mass emergence of flying, crawling, and creeping creatures. The timing of this double emergence is no accident. While the plant-eating insects feed, they also pollinate the flowers.

So beautifully coordinated are these adaptations that specialized flowers attract the very insects that do them the most good. Bees perceive color in the range of the spectrum from yellow through ultraviolet, and you will find them on the many yellow flowers of the pea family, blue larkspur, and lavender ruellias. Bees don’t distinguish red and orange, so they pass up the brilliant paintbrush which does attract hosts of butterflies. Flies, beetles, and other insects pollinate relatively unspecialized plants like the sunflowers. And night-flying moths respond to the whites and yellows that almost glow in the dark. In its caterpillar stage, the sphinx moth eats the leaves of the night-blooming evening primrose. When it matures the sphinx moth returns to the primrose and, hovering like a hummingbird, unrolls its retractable tongue and takes up nectar, thus paying its debt to the primrose by pollinating the flowers.

Insect-eating and seed-eating birds capitalize on each rain-induced harvest. The mourning dove, a common park resident, usually nests in the spring, but it may also nest again later in wet years. The scaled quail may produce as many as four broods in wet years, and you may see little brown chicks in mid-October. You may even happen on a young brown towhee high in the Chisos as late as November. Barn swallows and cliff swallows, both summer residents, nest as soon as they arrive in the spring, and breed again in wet years during August. The blackthroated sparrow may nest in both spring and summer if rains have produced a good crop of seeds, while the rufous crowned sparrow is actually busier nesting in wet summers than in dry springs. The black-chinned sparrow apparently waits for summer’s rainy season to nest.

Some mammal populations also rise and fall with the rains. Ord kangaroo rats may not breed at all during long periods of drought, but when a good rainy season produces an abundance of seed, most females soon become pregnant and produce two litters. Females of the first litter may even bear young of their own in the same breeding season.

As the Wild River Runs

At 3,000 meters (10,000 feet) the golden eagle glides on outspread wings, his head cocked down so he can watch for signs of life upon that motionless desert rolled out like a relief map below him. Largest of Big Bend’s airborne predators, the eagle needs an enormous hunting range, and riding the warm air currents high above the border, he can see it all: the flattopped and arched mountains, the sun-bleached lowland, and the silver Rio Grande disappearing and reappearing as it runs downstairs through steep canyons and open valleys. Tilting his two-meter (7-foot) wings, the eagle slipslides for a closer look into a canyon, spots the wake of a surface-swimming snake, folds his wings, and dives like a fighter jet. Before the snake even senses its peril, it is snatched aloft and hangs wriggling in the eagle’s talons as the great bird, feathered to the toes, lifts and flies up the canyon with mighty, measured wingbeats.

The waters dripping from the hapless snake’s body come from mountains far to the south and north. The Rio Grande begins in springs and snows high in Colorado’s Rockies, but backed into reservoirs and doled out to irrigate New Mexico and Texas farmlands, it may hardly even flow below El Paso. What gives the river a new lease on life is the Rio Conchos. This beautiful stream rises in the western Sierra Madres and flows northeastward across Mexico, cutting canyons of its own and joining the Rio Grande at Presidio, 160 river-kilometers (100 river-miles) above the park. Some geologists say it was the Rio Conchos, and not the Rio Grande, that cut those gorgeous canyons in the park. No one knows for sure. But once the river trapped itself, all it could do was dig deeper and deeper by processes that are still at work today.

A walk along a sandbar will show you that the river functions as a practical sorting machine. The water rolling by is so laden with sediment that you cannot even see rocks 13 centimeters (5 inches) below the surface. On the bar itself a layer of curling and flaking mud lies on top of the larger stones and gravel, which have fine sand deposited between them. The heaviest rocks settle out first, then the sand, and finally the finest particles. Water is a powerful lifting and pushing tool, but these water-borne abrasives do much of the river’s work, wearing out the rock, undercutting cliffs, deepening and widening the canyons. It goes on at normal stages of water where the river runs less than a meter (2-3 feet) deep, during floods when it crests at more than 6 meters (20 feet), and even during droughts when in many places the river is too shallow to float a boat. So in the slow course of geologic time the mountains are worn away, spread across the valleys, and carried out to sea.

The only streams that have a chance of leaving the desert alive are those whose water sources lie outside the desert. There are few such rivers in the world: the Nile, the Indus, the Tigris and Euphrates, the Colorado, and the Rio Grande. And what a wealth of water-loving life the wild river brings to the Big Bend desert. You can hang big catfish by the gills from your saddlehorn and have your horse walk off with fishtail dragging the ground. So the fishermen tell you.

Life in this watery world is sustained by a food pyramid based on a super-abundant supply of tiny bottom organisms. A third-meter (1-foot) square of riffle bottom has been found to contain more than 100 organisms. Most are larvae of flying insects: stoneflies, mayflies, dragonflies, damselflies, water and terrestrial bugs, various kinds of flies, midges, and dobsonflies. These curious little creatures have evolved ingenious ways of living, breathing, and eating underwater. Some worm-like caddisfly nymphs build protective cases around themselves, gluing pebbles, bits of shells, and plants together with saliva. They have three pairs of legs up front sticking out of the case and a pair of hooks holding on to it behind, so they can drag their houses with them as they feed. Damselfly larvae breathe through three leaflike gills that project from the hind end of the abdomen, and when warm weather comes they crawl ashore, split their skins, and emerge as gossamer-winged adults. The gills on stonefly larvae extend from the head and thorax, while mayfly nymphs have seven pairs of gills standing out like feathers along the sides of the abdomen. When oxygen is in short supply, mayfly larvae vibrate their gills rapidly so as to quicken the flow of water along their bodies. Some aquatic larvae build nets to catch dinner; a caddisfly nymph may spin a kind of silken windsock that he hangs underwater with the narrow end downstream, using the pressure of the current to keep his prey trapped. Some aquatic larvae eat microscopic plants, some eat insects, and some eat each other. Large dragonfly nymphs may even catch and eat small fish. Larvae are consumed by fishes, frogs, and turtles.

Probably the best way to get to know the river is to get out on it. An easy run is through Hot Springs Canyon, by 90-meter (300-foot) cliffs and over nice little rapids. You put in at the site of the old Hot Springs spa, and take out at Rio Grande Village, having to paddle only at riffles.

Suppose it’s early on a fine October morning and you’re floating along with the current, watching the sky, clouds, cliffs, and river cane reflecting blue, white, tan, and green on the glossy brown surface of the water. The river is too muddy for you to see what lives in it, but you can see the signs: a spreading circle where a fish has snatched an insect from the surface; mysterious little dimples that look like miniature whirlpools; the beaked head and long neck of a Texas softshell poked up like a periscope. This big turtle’s shell is really hard except along the edges, but it is smooth and doesn’t have the plates you see on other Rio Grande turtles. The Big Bend slider feeds primarily on plants, while the yellow mud turtle enjoys water insect larvae. And ready to oblige is a cloud of mayflies whirling in mad nuptial flight a meter or two (3-7 feet) above the water. They only live one day and exist as adults simply to mate, but they will sow the river with numberless eggs.

As you round a bend, a pair of great blue herons lifts from the shallows where they’ve been standing stilt-legged. Now with necks folded and long legs dangling they flap across to the farther shore. Ahead of you a blue-winged teal keeps lifting and settling further downstream. Ducks are seldom seen on the river in summer, but a dozen different species put down as migrants, and some even winter on the river. Now a slim pair of inca doves crosses overhead; you see the flash of rufous wings and white tail feathers. On a sandbar stands a spotted sandpiper, head low and tail high. He takes a step, stops, teeters up and down, and then flies.

The sandbar itself snugs in against the cliffside with greenery growing in three distinct tiers. River cane and mature salt cedar stand 4.5 meters (15 feet) tall against the flagstones. And stairstepped in front of these are seepwillows—not a willow at all, but a kind of sunflower that pioneers sandbars—and a younger, shorter stand of salt cedar. The canebrakes fairly crackle with wintering birds: black phoebes, cardinals, brown-headed cowbirds, and a migrating yellow warbler, perhaps. There is plenty for them to eat in that thicket. You yourself discover a nursery of orange true bugs beautifully crossed with olive green, all crowded together in every stage of development on two or three willow leaves. But the most intriguing thing about that sandbar is the record left by its visitors: a lizard’s five-toed track with the long unbroken mark made by its tail, and the great blue heron’s left-and-right footprints striding along almost in a straight line. You find the cat-like tracks of the ringtail, the dog-like tracks of the gray fox, and the flat-footed print of the hog-nosed skunk, pear-shaped as a bear’s. At the water’s edge honey bees are collecting moisture to water-cool their hive. One by one they sip and lift off, making a beeline for a cliff.

In the canyons where water flows from wall to wall, you find shore life restricted to those few plants and animals that can make a home on a cliff face. A spindly tamarisk has established a roothold in a thimble-sized deposit of soil just above waterline, and in cracks and crevices higher up, ocotillo and pricklypear are working down from the desert that tops the wall. Empty cliff swallow nests cluster on the undersides of overhangs. In spring you might see baby birds poking their heads from the colony’s doorways.

Along the border, people call the Rio Grande by its Mexican name, _Rio Bravo del Norte_. Nowhere does the river seem more wild, more powerful than inside Santa Elena, Mariscal, and Boquillas Canyons. To enter one of these mighty limestone vaults is to understand why mankind has always had to skirt canyon country, and why to this day, except for its historic fords, the river is all but impassable. If you go in by boat the only way out is through. The adventure calls for preparation, knowledge, hardiness, and considerable skill.

But even a landlubber can stand in the canyon’s primeval presence. All you must do is make it up the ramps and steps that climb the cliff face at the mouth of Santa Elena, then follow the foot trail down again into the canyon. Looking up from the base of these 450-meter (1,500-foot) walls, you see a vulture and a raven soaring side by side along the canyon’s rim. To them you must seem small and as foolishly occupied as the ants drawn up in opposing lines across the sandy path. One step and you could crush the horde. One rock fallen from that height and you are gone. One wild storm upstream and you, the ants, and the sandbar are all washed away forever. Yet you are somehow drawn farther and deeper into the canyon, into this jungle of dark green tamarisk and emerald bermuda grass, through this labyrinth of water-polished boulders, to land’s end and water’s edge, to the very Beginning that laid these fossil oyster shells in this fierce rock.

Here in the canyon’s deep, vault-like isolation the sense of time, that ominous, inhuman distance of the Earth’s past, may come over you as the imagined shadow of the wings of a prehistoric reptile, the Pterosaur, perhaps, from 65 million years ago. This was the biggest flying animal ever known to have lived. Picture a 70-kilo (150-pound) flying reptile with a wing spread of up to 11 meters (36 feet), a foolishly long neck, and large head with a long, slender, toothless jaw. Add long legs, and short toes armed with sharp, hooked claws, and a body covered with fur-like material. And figure that each of those long, narrow, glider-type wings was a thin membrane supported by a single overgrown finger, and attached to the body, bat-style, right down to the knee. How could such a huge, ungainly thing ever lift off or fly?

A species does not survive unless it can compete for food and escape its predators, and Pterosaurs, both large and small, existed alongside aggressive, meat-eating dinosaurs for 140 million years. Unlike some smaller species found elsewhere, the Big Bend Pterosaur does not seem to have fished the ocean. At that time, Big Bend offered a river and floodplain environment far from the sea. No one knows how this giant Pterosaur made its living.

How the Canyons Were Formed

Some 200 million years ago this region lay under a sea whose sediments
formed the structural, limestone bedrock patterns of the Big Bend. The
basic landscape configurations of today’s park were set in motion 75
to 100 million years ago as the landscape emerged, folded, and
faulted. Then erosion set in.

The ancestral river that carved Santa Elena, Mariscal, and Boquillas
Canyons through bedrock was the Rio Conchos. (The present Rio Conchos
contributes most of the water flowing through today’s Big Bend. It
flows into the Rio Grande just upstream of the park.) When the
ancestral river hit the limestone mountain uplifts, it had no
alternative but to cut its way through. Steep-walled, narrow canyons
resulted. Santa Elena Canyon is cut through the Mesa de Anguila.
Mariscal Canyon severs its namesake mountains. Boquillas Canyon, the
longest, cuts through the massive limestone Sierra del Carmen. You can
see how steep these canyons are by taking a river trip (see page 122)
or hiking park trails (see page 119) to the river or to canyon rims.

The region was once much higher in elevation than it is today, but
erosion has taken its toll. Mountains and mesas are landscape
formations whose rock erodes more slowly than surrounding materials
do. Castle-like peaks and high, sharp-rimmed mesas stand as weathered
monuments to earlier times when elevations were higher. Such stranded
vestiges of geologic eras punctuate the stark Chihuahuan Desert
landscape with eerie architecture. Astronauts have used Big Bend
terrain to simulate moonscapes.

The sequence of geologic diagrams shows how the Big Bend canyons
formed and what their future would be if slow processes of erosion
continue.

When you think that the Earth is perhaps 4.5 billion years old, that complex organisms have existed for no more than about 700 million years, that the oldest rocks exposed in the park are 300 million years old, and that fossils of backboned animals in the park cover a time span of 70 million years, you can realize how fragmentary the fossil record really is. You get few glimpses of the relatively recent past, but these are astonishing.

For example, geologists know that back in the dim dark distances of Earth time, Big Bend lay repeatedly at the bottom of the sea. Convulsions within the Earth repeatedly raised these sea floors to the tops of mountains, and time after time these mountains wore away. One of the ancient ocean beds can be seen at Persimmon Gap where, in remnants of the park’s oldest mountains, fossil sponges, brachiopods, and other simple marine organisms lie exposed. For hundreds of millions of years the three-lobed trilobite was among the most prolific animals in the world, but it had long been extinct when the last great ocean, the so-called Cretaceous sea, washed across Big Bend. Most of Mexico lay submerged and a sort of mid-continent seaway cut North America in two about on the line of the Rocky Mountains. In its early stages this sea harbored ancestral clams, oysters, snails, corals, and a coiled shellfish called an ammonite. You can see these animals preserved in the limestone walls of Santa Elena Canyon. Giant clam shells a meter (3 feet) across and fossil fishes preserved in the round between Boquillas and Mariscal Mountain tell us what lived in later seas. Sea turtles, sharks, and a 9-meter (30-foot) marine lizard that swam in the open ocean have left their remains in the yellowish badlands near the park’s western entrance.

Late in this oceanic period the Rocky Mountains began to rise to the north of Big Bend, the Sierra Madre to the south. The park’s own Santiago, del Carmen, and Mariscal ranges, and the first upward thrust of the Chisos also occurred at this time. As the mountains rose and started to wear away, delta deposits began to build out farther and farther into the seaway, forming barrier bars and tidal shelves where turtles, snails, oysters, and sharks lived and died. Gradually the near-shore, subtidal environment changed to a tidal flat. This in turn changed to marsh, to beach, to brackish and freshwater lagoons, and finally to an estuary and river floodplain environment. Such was the Big Bend world to which the dinosaurs came. They had been ruling the Earth for eons, but they did not reach the park until the Cretaceous sea withdrew.

Sloshing about in the freshwater were amphibious and semi-aquatic species. Probably commonest was the duckbill dinosaur, an enormous reptile that walked on huge hind legs. It had as many as 2,000 teeth. Specially adapted for grubbing up and munching freshwater plants, these flat grinders occurred in batteries in the duckbill’s jaw. As a tooth wore out, another popped into place.

Tramping about on all fours and peaceably cropping land plants were bizarre looking horned dinosaurs with turtle-like beaks. For their weight they must have had the most powerful jaws of any backboned animal that ever lived. Armored species included one that looked like a horned toad the size of a dump truck. Another sported a huge lump of bone on the end of its tail, still another a thick lump of bone above a brain no bigger than the end of your little finger. The world’s largest crocodile, a 15-meter (50-foot) creature with 15-centimeter (6-inch) teeth, turned up in the park, but remarkably few bones of meat-eating dinosaurs have ever been found. One of the Earth’s great mysteries is why, at the top of their terrific form, the dominant dinosaurs died out? This happened in a geologically short time all around the globe. Perhaps it was because the highly specialized reptiles couldn’t cope with changes in their environment as the world climate grew cooler and more continental. No one really knows.

When the Age of Mammals began some 64 million years ago, Big Bend lay on an alluvial floodplain where summers were moist and winters were mild. Shallow rivers meandered between natural levees wooded with flowering plants, sycamore, stinking cedar, and tree ferns. Garfish swam in rivers and isolated ponds, while small lakes and swamps lingered on in meander cutoffs and abandoned river channels. It was a land where seasonal floods alternated with dry periods and where, during protracted dry spells, treeless areas invaded the forest.

The Fossil Record

Garfish and turtles in the Rio Grande give us a hint about life here
50 million years ago. Then they swam in waters haunted by crocodiles
and visited by the modern horse’s earliest ancestor, Hyracotherium;
the hippo-like Coryhodon; and Phenacodus, an early species of ungulate
related to both hoofed and clawed mammals.

Fossils of these and other animals belie dry and barren Tornillo
Flat’s earlier Eocene life as a lushly vegetated landscape, as
depicted in this reconstruction.

At the time of this scene the dinosaurs (“terrible lizards”) had been
extinct for 15 million years. Their fossils occur here too. Remains of
the giant Pterosaur have been found. These “winged lizards” were
flying reptiles whose 11-meter (36-foot) wingspan exceeded that of
small jet fighters. The wing was a featherless membrane stretched out
from the reptile’s body to the tip of its greatly enlarged fourth
digit. Fossil remains of Brontosaurus, Allosaurus, Icthyosaur, and
others have been found. Fossil Ammonites (see page 67), related to
today’s sea-dwelling chambered nautilus, represent the even earlier
period when today’s Big Bend was covered by a shallow inland sea.
Sample fossils are displayed in a shelter off the Marathon entrance
road near Tornillo Creek bridge.

With such a wealth of habitats a whole new host of animals took over Big Bend. Crocodiles and turtles hung on from the Age of Reptiles, but nature’s evolutionary torch passed to the warm-blooded mammals who increased rapidly in numbers, size, and diversity. Remains of 29 species of early, extinct forest-dwelling mammals have been discovered near the Fossil Bone Exhibit site on Tornillo Flat. This same floodplain later accommodated a hippo-like plant-eater, a browsing collie-sized mammal, a panther-like cat, and the little ancestral horse, Eohippus. No bigger than a fox terrier, Eohippus had not yet developed the typical horse hoof and still had four toes on his front feet and three on his hind. He browsed among low forest plants, because nature hadn’t yet invented grass.

Some 20 million years ago, when we get our next glimpse of the Big Bend, grasses were well established and the Earth began to witness the rapid rise of grazing animals. In the park, Castolon had a savanna-type environment, with a sub-humid to semi-arid climate. Rabbits and camel- and sheep-like mammals flourished. Plant eaters ranged in size from a tiny mouse to an enormous rhinoceros. This giant was about 3 meters (10 feet) long, stood 2 meters (7 feet) high at the shoulder, and had massive, bony horns on its head. There were also carnivores to fatten on the herbivores.

In the middle of the Age of Mammals, Big Bend country became the seat of widespread and repeated volcanic disturbances, with lava flows, ash falls, and mountains bulging up like blisters as they filled with molten rock. Here, most of these events centered on the Chisos, where the signs can be seen in mountain peaks to this day. Much of what happened since has not even left a shadow; the record and the rocks have both been erased by millions of years of weathering and erosion. But you can see “living fossils” in the high Chisos canyons. These are the ponderosa pines, Arizona cypress, and Douglas-fir trees descended from the moist woodland species that populated this region during the last Ice Age. Occasional remains of the great Ice Age mammoths have also come from gravels in deeply eroded ravines. And you can see all around you the evidence of two latecomers who seem to have reached Big Bend around the same time: Man and the Desert. But here, deep in the river’s canyon, both are apparently as remote from you as your own daily world.

Along the Greenbelt and Among the Grasses

Even in the dead of night it smells green beside the silt pond at Rio Grande Village. Well, _dusty_ green perhaps, but redolent with reeds and shrubs, trees and grass, with the very jungle breath of the floodplain. On the other side of the river a lone cock crows and close at hand there’s a rustling of leaves, a crackling of reeds, the lap-lap of some animal drinking. Leopard frogs croak on in unconcerned bass and baritone burps, sounding like someone’s stomach talking. But all at once something has a frog for dinner and the unwilling meal keeps pumping out shrieks, faster and faster and louder and shriller, to the last breath. Then silence. The frog chorus grumbles on.

In the morning you find the flat-footed tracks, long-fingered as a human hand, of that nocturnal hunter. The raccoon is an omnivore, an opportunist with a taste for whatever it can find: amphibians, shellfish, mesquite beans, acorns, cactus fruits, rodents, garbage. The little masked bandit can in fact make himself a campground pest. His dependence on water keeps him a prisoner of the floodplain, but the river, the springs, the sloughs, and the ponds provide abundance in a narrow green world unrolled like a ribbon across the desert. Sometimes this greenbelt, as it is called, is no wider than a bush; in places it may measure three-quarters of a kilometer (half a mile). And it keeps changing, widening with floods, narrowing in droughts, altering course with the river itself.

Just such a change of channels apparently created the bench of bottomland where Rio Grande Village lies today. People have been camping here for thousands of years, as shown by the many deep mortar holes where meal was ground in the limestone ledges near the pumping station. Certainly the place had much to recommend it: wood and water, abundant game, rich soils, an agreeable winter climate, and beautiful views of river and mountains. After the white man came to stay in the early 1900s most of the native flora changed. Farmers cleared the bottomland to plant cotton and grains, cut down the lanceleaf cottonwoods for roofbeams, dredged ponds and ditches, and enclosed springs. Nowadays, the plants you see are often exotics brought in from outside to create shade and lawns.

Such are the eastern cottonwoods with their heart-shaped leaves, the evergreen live oaks and smooth sycamores, the sweet-smelling honey locust and eucalyptus trees, and that fine green carpet of Bermuda grass. Like the farmers’ field crops, these interlopers cannot flourish without irrigation and sometimes even that is not enough. Dozens of eastern cottonwoods have died in recent years.

A good place to see native plants and animals is along the Rio Grande Village Nature Trail, which starts at the campground and leads to a hill above the river. A walk along this trail is doubly interesting because it shows greenbelt and shrub desert side by side, the two habitats often separated by less than a vertical or horizontal meter. The jungle starts at the edge of the clearing and almost at once you come upon a warm spring run. This may be where the rare little Big Bend mosquitofish, _Gambusia gaigei_, originated, but all you see today is a larger relative, _Gambusia affinis_. These five-centimeter (two-inch) predators, little as they are, soon take over. They apparently are invaders from the Rio Grande.

In wet weather this whole spring area becomes a swamp and even in dry times moisture-loving plants crowd the trail. You pick your way beneath black willow trees and grapevines festooned with wild grapes, stop to admire the yellow tube-flowers on the tree tobacco, stoop to avoid a spear slanting from the solid wall of common and giant cane. These two tall woody grasses stand 4.5 meters (15 feet) high and put out great, plume-like flowering heads that shine silver in the sun. Indians used the stems for arrow shafts and ate the roots raw, roasted, or boiled. Many an early settler roofed and even walled his house with cane. Today the reeds supply deer and cattle with attractive browse, and the thickets serve both as home and hunting ground for birds, small mammals, and reptiles.

Here is the cleverly constructed nest of a gray wood rat. And there, crouched beneath a bush like some storybook monster is an enormous spiny lizard. Rosy and gray, he peers back unblinking, still as a stone, then melts away so quickly he is gone before you see him move.

A little further on the trail climbs a short rise, topping out on Chihuahuan Desert complete with creosotebush, dog cholla, ocotillo, and the standard collection of cactuses. If you take the trail in spring or summer, the mound-building strawberry cactus will be covered with hot pink blossoms and delicious fruit. By fall the fiercely barbed blades of the false-agave, or hechtia, will have taken on a reddish tinge. In wintertime the tasajillo cactus will be dressed like a tiny Christmas tree in long green spines and bright red fruits. But at any season this water-starved scene stands in sharp contrast to the marsh, rank with reeds and bulrushes, that lies just below.

Unlikely as it may seem you are looking at a beaver pond backed up behind an actual beaver dam hidden in the reeds. The wary, nocturnal beaver is seldom seen and you will look in vain for the familiar beaver lodge, because Big Bend beavers make do with what the floodplain has to offer. Instead of building wooden houses, these rodents dig burrows in the river bank, foraying from there to feed on willow, cottonwood, seepwillow, and river cane. Around the turn of the century the Rio Grande and its main tributaries abounded with beaver, but fur traders trapped them to the brink of extinction, woodcutters and farmers destroyed their food supply, and cattle feeding in the canebrakes trampled their burrows.

It is hard to imagine just what destroying the trees and ground cover can do to fertile land and to a living stream, but a visit to Terlingua Abaja shows you. James B. Gillett, foreman of the famous G-4 Ranch, recalled that in 1885 “the Terlingua was a bold running stream, studded with cottonwood timber and was alive with beaver.” There was one grove of trees where he had seen at least 1,000 head of cattle enjoying the shade. But after the Terlingua mines opened, Mexican farmers established a community at Terlingua Abaja, a few kilometers up the creek from its junction with the Rio Grande. All the cottonwoods up and down the creek fell to construction and hungry mine furnaces and the virgin earth turned bottom up beneath the plow and grubbing hoe. Today this once fertile valley is a wasteland.

The Rare Big Bend Mosquitofish

The Big Bend mosquitofish (_Gambusia gaigei_) has a miniscule
geographic range. Not only is it restricted to the park, as some other
species are, but it is also restricted to one pond. The fish was first
identified in 1928 in Boquillas Spring. Unfortunately, the spring soon
dried up and for some 20 years the fish was thought extinct. In 1954
more were found near Rio Grande Village. This group was later
threatened, and a pond was built especially for the fish. But people
dumped into the pond other fish that ate this tiny mosquitofish. At
one point the world’s only survivors were two males and a female, Rio
Grande Villagers that biologists had removed to a laboratory aquarium
at the University of Texas at Austin. A cold winter again killed
nearly the whole park population, and again the Austin-raised stock
replenished it. _Gambusia gaigei_ gives birth to live offspring and
has been around as a species since mastodons. They feed largely on
mosquito larvae.

Since the coming of the park, cottonwoods have returned to the floodplain, especially at Castolon. A stately colonnade of eastern cottonwoods lures ladderback woodpeckers and yellow-bellied sapsuckers to Cottonwood Campground. More than 100 lanceleaf cottonwoods may be seen along the road that leads to Santa Elena, Mexico. Standing as much as 30-meters (100-feet) tall, refreshingly green in summer and gorgeous gold in fall, cottonwoods seek water by spreading horizontal roots far and wide, and by sending taproots deep down to the water table. They propagate in early summer by shaking millions of cottony seeds upon the wind. These fuzzy white parachutes may lie in windrows or cover the ground downwind like new fallen snow.

Along the River Road from Castolon to Santa Elena Canyon, you get another glimpse of what water means in the desert. The road winds along the edge of an alluvial bench from 15 to 30 meters (50-100 feet) high. Atop this terrace you have the widely spaced shrubs of the Chihuahuan Desert, but peer over the edge and you find a dense green wilderness crowded between the benchface and the river. All that separates lifeless sand from green jungle is the vertical distance that stops the water. Down there salt cedars have packed themselves thickly into the narrow space.

Another water-loving plant prevalent along the river and dry washes is honey mesquite, a feathery, thorned shrub- or tree-sized member of the pea family. Its root system, with a deep tap root, is so extensive that more wood lies underground than shows above ground, and natives say you must “dig for wood” here. Mesquite trees multiply as persistently as salt cedar, but are highly useful to man and to wildlife. Honey bees and butterflies visit the yellow mesquite flowers, quail roost in the branches, and wood rats collect mesquite beans in tremendous numbers. Deer, horses, and cattle also relish the beans, while Indians and early settlers made a nutritious bread from mesquite bean flour. Honey mesquite carries the standard Kentucky-wonder type of bean. But the screwbean mesquite or _tornillo_—for which Tornillo Creek was named—puts out a curious cluster of corkscrew-shaped fruit pods. Mesquites often mass together in thickets, and they do very well in the drier soils of arroyos, often rubbing thorns with acacias, a family of sweet-smelling, flowering trees and shrubs attractive to honey bees and hummingbirds. The roots of these thickets provide apartments for scores of floodplain pocket gophers, kangaroo rats, and hispid cotton rats.

Despite the luxuriance and rapid growth of floodplain flora, life along the greenbelt rests in precarious balance. The floodplain is the one place in the park from which domestic cattle have never been successfully removed. The problem is that Mexican cows, horses, and burros do not recognize international boundaries.

There was a day when cows grazed grasslands at higher elevations, and before the cows could be seen herds of pronghorns, golden, graceful, large-eyed, with black horns and white rump patches. Imagine if you can how Tornillo Flat must have looked at the turn of the century with fine grasses bending under the wind and the pronghorns flashing their rump patches in sudden semaphore. Depending on speedy flight for protection, pronghorns seek wide-open places where they can see a long way off. Today, Tornillo Flat is a bald shrub desert. The pronghorns vanished long ago. The small band sometimes seen north of Tornillo Creek is the remnant of a herd reintroduced in the 1940s.

The grass that flourished on Tornillo Flat in its heyday was a very good clump-forming grass called tobosa. To the first settlers it looked as though there was more grass along Tornillo Creek than could ever be eaten off. Yet the tobosa soon disappeared, falling first to mowing machines and finally to the domestic herds that cropped it out of existence. Hay balers plied Tornillo Flat into the 1930s.

Grasses spread through seed germination, and in some cases by underground and aboveground stems. As a general rule, root depth equals the height of the grass, but half of the root system dies back each year. This is natural and even desirable since the dead roots create new soil and you still have a sound root system if the grass isn’t topped too much. But heavy overgrazing causes grass roots to die back even more and creates an abnormally shallow root system. This is doubly dangerous in desert country where heat and the need to search out water pose crucial problems for all plants. Nor is this all, because other good things come—and other good things go—with a healthy ground cover. As each year’s grasses die back they fertilize the soil and insulate seedlings and roots from the sun’s killing heat, but when this cover is reduced, good grasses disappear and poorer grasses take over. Surface conditions are finally so changed that neither grasses nor grassland forbs and shrubs can grow. Seedlings may burst into brief life with a rain but when the sun bears down again day after day the unprotected plants perish. With nothing to hold it the soft topsoil blows and washes away. Desert downpours soon gully the ground, changing drainage patterns and lowering the water table beyond the reach of short grass roots. Longer rooted desert shrubs move in, first the shortlived tarbush, and finally creosotebush. The result is seen on Tornillo Flat today: typical Chihuahuan shrub desert with sparsely scattered creosotebush and cactuses.

What happened at Tornillo Flat also happened to other park grasslands. Chino grama, ignored by cattle and goats, but relished by sheep and horses, is and was the dominant grass of the Big Bend foothills. By 1944, overuse had so stripped the grasslands near Government Spring that you could hardly find a bunch of chino on the bare beige hills. Even in the mountains proper the grasses had all but disappeared, and biologists conducting an ecological survey found that the South Rim looked and smelled like a goat paddock.

Once the park was established and domestic animals were removed, native grasses got the chance to reestablish themselves. At first nature itself blocked recovery. For seven long years drought ruled all life in Texas. When the rains finally did come, grasses improved at different rates in different places. They had the most difficult time at lower elevations where heat and aridity are greatest. Several attempts to seed Tornillo Flat have been made, but it may take decades for these once bountiful bottomlands to green again. Grasses in the grassland belt surrounding the Chisos have made a remarkable comeback, however. In ten short years ground cover increased 30 percent. Grasses at the higher elevations are now probably as rich as ever.

The Fur Trade

Furs were an active commodity in the Big Bend until about 1940. Beaver
once abounded along the river and its tributaries. Both fur bearers
and predators were taken. The bighorn sheep was largely extirpated,
selling for a time as “Mexican goat.” Wolves were extirpated before
the park could provide refuge. Not all species were trapped. The
javelina was hunted during World War I, for use in gloves, coats, and
suitcases. The bristles went into brushes. Elmo Johnson (photo) bought
furs from trappers at his trading post. Good profits required a good
eye for raw furs, which Johnson possessed. Furs not trapped during the
animal’s winter prime were nearly worthless, and values depended on
their condition generally. No fur market existed in Mexico, so furs
trapped there were sold at Texas trading posts, destined for the fur
houses in St. Louis, Missouri. Only a portion of Johnson’s fur stocks
shows in this 1929 photograph. Furs were a good business for him,
because trappers took their value in goods, his first profit in the
transaction. He then sold the furs for his second profit. Later,
salaried government trappers worked this area to control predators.
Today, all wildlife in the park is protected.

Different kinds of grasses have adapted themselves to different soils and altitudes and grow in company with different co-dominant plants. In colorful sequence the grasses create a three-dimensional mosaic that begins on the edges of the shrub desert, covering the foothills and running up through the woodlands out onto mountaintop meadows. You can see these differences quite easily.

Let’s say it’s ten o’clock on a fine fall morning, and you are driving from Rio Grande Village up to the Basin. You find shrub desert all around you at first, with the usual creosotebush, ocotillo, and pricklypear. The only grass you see grows in a buff-colored strip on either side of the road, where runoff from infrequent rains creates a habitat moist enough for grasses to germinate and reach maturity. But after you pass 900 meters (3,000 feet) of elevation you begin to see the first sparse bunches of chino grama spotted here and there across the desert. Somewhere just below the Dugout Wells turnoff you find quite a bit of bunch grass among the bushes. Almost imperceptibly the chino thickens until at 1,000 meters (3,500 feet) the hillsides appear cobbled over with lumps the color of gray rock. It appears that you couldn’t step down without stubbing your toe against a clump of gray-green grass or lechuguilla. Soon all the slopes are patterned yellow and gray-green as solid stands of lechuguilla crowd into the chino grama. The grass is so thick now that scaled quail hunt seeds along the roadside and cottontail rabbits bounce jauntily across in the mid-morning sunlight.

The colors you see owe much to the angle of the sun, but at about 1,200 meters (4,000 feet), near Panther Junction, the plants themselves add a soft new hue, the beautiful silver-blue of ceniza shrubs. Bunches of vivid green grass crop up amid the tawny three-awns by the roadside, and the tops of the tarbush are brushed with yellow. Rock, gravel, grass, and shrub blend together in shades of tan, gray, green, and blue pinpointed by Christmas-red fruits on the guayacan, with once again vast gardens of chartreuse lechuguilla and skeleton-leaf goldeneye shrubs. These rolling grasslands have much less pricklypear and creosotebush, and they have a lower profile than the shrub desert. Here and there the Torrey yucca lifts its shaggy head high, but the whole land surface looks somehow smoother, less hob-nailed than before.

When you start the 11-kilometer (7-mile) climb toward the Basin, chino grama gives way to a variety of grasses, blue, black, hairy, and side oats grama, and the straw-colored grass aptly named tanglehead. The whole color scheme changes with the grass from shades of gray to reddish brown and yellow, and the tops of these good grasses have the heavy headed look of grain. The lechuguilla becomes less obvious. Gradually the moisture-loving mountain shrubs push the grasses back from the roadside, but the golden gramas grow with wonderful abundance on the drier slopes beyond. Still higher, the still good grasslands are studded now with century plant, basket grass, and sotol.

Earlier in this century sotol abounded between Green Gulch and Government Spring, but in the severe drought during World War I, ranchers chopped it out for cattle feed. Today you will find a perfect forest of sotol growing at Sotol Vista on the western flank of the Chisos. As you can see from the overlook, this narrow-bladed plant favors the cooler north-facing exposures. Sotol leaves grow at ground level from a short trunk, and nearly every spring the plant thrusts up a brush-like bloomstalk, 4 to 6 meters (15-20 feet) tall, covered half its length by greenish-white flowers. Prehistoric Indians had many uses for sotol, and later the Chisos Apaches often located their rancherias at solid stands of “desert candle.” They used the fibrous leaves in making mats and ropes, fermented a potent drink from the pineapple-like heart, or roasted it in rock-lined pits as we roast beef. Several crumbling sotol pits are found throughout the Chisos, and sotol still serves as an all-purpose plant along the border.

Sotol is one of those Big Bend plants that has its very own grasshopper. If you look closely, you may find a little fellow feeding high on the bloomstalk and looking for all the world like a bud. He lives his whole life on the sotol plant and knows just how to use it to advantage. If you annoy him he will probably play possum, drawing in his legs and dropping like a stone right down into the thick of the sotol leaves. Few predators come away unscathed from a close encounter with those saw-edged blades.

Indians of the Big Bend

Evidence of Paleo-Indian culture dates back to about 9000 B.C. here.
The Archaic and Neo-American culture sites date from about 6000 B.C.
These occur near today’s water sources, so climate conditions then
were probably similar to now. The Archaic people used the atl-atl, a
dart-pointed throwing stick, to hunt game animals. The Neo-Americans
used the bow and arrow. Spaniard Cabeza de Vaca encountered their
descendants in his 1535 expedition through the area. In the 1640s the
major Indians here were the Tobosas, Salineros, Chisos, and
Tepehuanes, who fought Spanish encroachment and enslavement. Spanish
horses enabled the Mescalero Apaches to expand their range and
dominate the area by the 1740s. They became the Chisos Apaches. By the
1840s, the Comanches, also with Spanish horses, dominated an enormous
range focused on the Big Bend. When Texas was annexed by the United
States in 1845, the U.S. military became the Indians’ antagonist.
Forts strung along the route to California goldfields after 1849
sliced the Indian territory in half.

Retreating far into the mountains, the last Apaches, under Chief
Victorio, were defeated by Col. Benjamin H. Grierson and scattered
into Mexico. There Victorio was soon killed by Mexican troops. Col.
William H. Shafter continued the Army’s Indian pacification after
March 1881. Not all Indians were hostile. The painting, by Capt.
Arthur Lee, shows West Texas Indians trading at Fort Davis.

Another lily of the desert is the yucca. Overabundance of this perennial often indicates abuse of a grassland, and yucca gradually thins out again once a good grass cover is reestablished. Several species of yucca flourish in Big Bend. Most widely scattered is the Torrey yucca or Spanish dagger. Seen from desert lowland to mountain top, it thrives at Persimmon Gap near the park’s north entrance.

Yucca grows like sotol from a central trunk, but it adds new growth at the top and lets its dead leaves drop down in a palm-like grass skirt. The yucca also puts up a bloomstalk year after year, and the creamy flowers are a favorite browse of deer and cattle. Yuccas may live from 50 to 75 years, reaching tree-like proportions. The giant dagger that gives Dagger Flat its name may grow more than 6 meters (20 feet) tall. In good years it blooms around Easter-time, and a single bloomstalk may have more than 1,000 flowers and weigh as much as 30 kilos (70 pounds). Indians used nearly every part of the yucca in countless ways. They ate the flowers and fruit, wove baskets and made brushes from leaf fibers, and made soap from the roots. Along the border, natives still harvest the great yucca flower-heads and feed them to livestock.

The Mescalero Apaches roasted the mescal or century plant using the same technique they used for sotol. The mescal was as central to the Apache way of life as the bison was to the plains Indians. They made food, drink, medicine, mats, ropes, bags, and even needles and twine from the great, gray-green agave.

It is not true that the century plant takes a hundred years to bloom; it’s more like 25 to 50 years. Once started the bloomstalk shoots up at the rate of nearly 2.5 centimeters (an inch) in an hour, or up to 41 centimeters (16 inches) in 24 hours. Soon platters of golden flowers float on the air, and bees, flies, and ants come to the feast. The violet-throated Lucifer hummingbird may sometimes be found at a mescal in blooming season. At night the Mexican long tongued bat leaves its cave on Emory Peak and comes to feed on the nectar and ample pollen.

Like all agaves, the mescal expends its strength on this onetime burst of blooming. Once the seed pods form, the plant dies and young plants arise near its base. But that is not the end of its beauty or its usefulness. If you climb the foot trail to Juniper Flat through the thickly grassed woodlands above the Basin, you will pass more than one dead mescal with its towering bloomstalk supported by the limbs of some pinyon pine. Year by year, in graceful and gradual decay, the agave leans in its neighbor’s embrace. As it slowly splits up, it dresses the pine in a flowing drape of fiber fragments. You can see little wormholes here and there, and larger holes where woodpeckers have taken a meal. This life-supporting return to dust goes on all over these mountains.

Many of the park’s finest grasses may be found in the mountains, for while the grasslands blend into the woodlands somewhere around 1,700 meters (5,500 feet), the grasses continue all the way up to the mountaintops. Again, the species change with climate, altitude, and ground cover conditions. The beautiful bull muhly favors north-facing slopes, and, growing in clumps up to just over a meter (4 feet) high, it helps hold soil on the hillsides. With its large purple flowering heads, it makes a good bedding grass for deer. So does the golden thread-leaf stipa that likes to grow under juniper trees, spilling its long blades in rounded clumps.

Since the return of the grasses the mountains and foothills both support a fascinating host of grassland animals. Some, like the yellownosed cotton rat, have come back with the grass. Many of these grassland creatures are abroad at night and are best seen at dawn and dusk. Even after dark you may see a great deal of life along the highway. The 16-kilometer (10-mile) stretch between park headquarters and the Basin may bring startling glimpses of grassland activity within reach of your headlights: a great horned owl with its catlike face and “ears,” sitting still as a sphinx in the middle of the road; a coyote pair gamboling like shepherd pups, their paired eyes flashing white and bright as automobile headlights. These carnivores have come to hunt the rats and rabbits making a mad dash across the road. Arthropods and snakes come to the pavement to warm themselves. The diamond sparkles that litter the blacktop may be reflections from spiders’ eyes. You see a blood-red coal of fire spring to one side at the edge of the road and then as abruptly as a UFO leap 3 meters (10 feet) straight-up into the air. A ringtail climbing a tree perhaps? Or a poor-will taking flight? A flash of pink lights at elbow and shoulder height turns out to be a mule deer and fawn. Stop, turn off your own lights, and look and listen and you will behold a world as it must have been a long time ago, singing in the silence underneath the stars.

Bandits and Revolutionaries

When the deepest channel of the Rio Grande became the boundary between
the United States and Mexico in 1848, the Army assumed a thankless
task: To enforce an invisible boundary in impossible terrain
populated—if at all—by people traditionally disposed to crossing the
river freely. At times the Army depended on the Texas Rangers. During
the Civil War era troops were withdrawn from the Big Bend, and border
incidents surged. After the Mexican revolution of 1910 that government
lost control of its northern provinces. Bandit gangs plagued both
Texas and California. Pancho Villa used border forays to create
tension between Mexico and the United States. In 1913, raiding bandit
Chico Cano was captured and freed by his gang in an ambush; the next
year he killed his Customs Service captor. Cano was photographed with
8th Cavalry Major Roy J. Considine in 1918. Three soldiers and a small
boy were killed in a 1916 raid on Glenn Springs led by Navidad
Alvarez, a lieutenant of Pancho Villa. The store was looted and houses
burned. Livestock raids on ranches sometimes left entire families
murdered. Many Texas Rangers were killed in ambush over the years.
Smuggling activities abounded. Arms and ammunitions passed into
Mexico, and liquor (during prohibition) and silver bullion passed into
the United States.

Where Mountains Float in the Air