 A presentation of the United States Fish and Wildlife Service. In Southern Arizona, along the Mexican border, is one of the most inhospitable and desolate places in North America. Here on close to a million acres of Sonoran desert lies Cabesa Prieta National Wildlife Refuge, a place as wild and grand as any in North America. Bill Broils, a high school teacher in Tucson and a refuge volunteer, has been exploring the Sonoran desert for more than 25 years. Bill has written extensively about the history of the region and devoted much of his life to learning about this fascinating ecosystem. The geology of the Cabesa Prieta is so spectacular because it is so young. Most of it began within the last 70 million years. This is the base in a range province, which means that most of the mountains are quite linear. And if you look at your map, you'll see them stretching from southeast to northwest. The mountains are of two different types. The granite mountains, which rise abruptly out of the desert floor, and also the basalt mountains, such as you will see over in the Growler Range and also the top of Cabesa Prieta Peak, which is the black lava cap on the blonde granite beneath. These mountains are separated by wide valleys, which are filled in with sediment from the eroded mountains. But the mountains themselves, because there's so little rainfall here, are very steep and very jagged and rugged coming directly out of the valley floor. As desolate and harsh as these bare mountains and valleys appear, people have hunted and gathered food here for thousands of years. There are places on the refuge that are sacred to the Native Americans who descended from these ancient people, many who still live in the surrounding area. Trails that were used for hundreds of years are still visible on the valley floors. Visitors to the refuge can travel on one of the more famous of these ancient rooms. We're walking the El Camino del Diablo, the infamous Devil's Highway. It is a segment of an old network of trails that prehistoric peoples used in this area to crisscross their way between waterholes, hunting grounds, campsites. You still see some of their trails out here, potchards, stone tools, and even seashells that they brought back from the Gulf of California. They are long gone, but when the first European explorers came through this area, in 1540, Melchior Diaz, for example, he followed their trails. And Father Quino in 1698 and several trips thereafter, he too took these same trails guided by the Indians living here at the time. The road has always been very adventurous, severe, and risky. It took a lot of courage to come through the heat. For example, here's one grave of a passerby who did not survive the trip. And a number of them did not survive the trip. The Cry of Gold in 1848 brought a number of people to California by this route. They came unprepared. They came in summer to be the first ones at the gold strike. And one observer reported as many as 400 graves along the stretch between Senoida in Sonora and Yuma in Arizona along the Colorado River. Another observer reported a string of mummified livestock, broken wagons, bleached bones. The first motorized car to come through here was Rafael Pompelli in 1915. And if Rafael or even some of the 49ers or prehistoric people were to drive with you out here on this road, they would recognize the same landmarks, the same terrain, and they would be quite comfortable with you. You also would have the same problems that Rafael had. You would have broken radiators, punctured tires, bulky engines. And so he, like you, would have come prepared to drive this treacherous road. Being prepared means not only having the right equipment, but carrying at least a gallon of water per person per day while traveling on Cabeza. For early travelers knowing the location of the desert water holes, or tinajas, Spanish for tank, was a matter of life or dying of thirst. This cryptic arrangement of stones estimated to be more than a century old points west towards tinajas altas, one of the few places where water was usually assured. Closer by through this pass, a canyon leads to a tinaja that has seen much history. Several times a year the rains will come coursing down this canyon and fill the tank, but then the hot sun, thirsty tongues of animals may deplete it. If we were a prehistoric person or a historic traveler on the El Camino del Diablo, coming by foot or by horse, this is one of the few water holes on the entire route. And if water is here, we are saved. If not, we have to march 20 more miles to tinajas altas to find water. We, unlike some of the desert species, can't get along without water. So this place was a very important campsite for prehistoric people. Collectively, they were known as Amargossans, Patayans, Hoho-Coms, and most recently, Yacherotams, also known as San Papago. They lived in this stark country. They thrived in this country. There are always very few of them, and they relied upon these natural cups of water in the granite or in the basalt. These water holes all had names and histories and people would come into the canyon to camp, to gather food, to gather seeds from the mesquite beans, from the Palo Verde trees to use as their food. They were also, of course, hunt. Another important food source for early visitors to Cabesa Prieta were the desert bighorn sheep, who were hunted as they came down from their rocky crags to drink at the water holes. This noble animal, much admired for its desert savvy and magnificent horns, is today highly prized by big game trophy hunters. In fact, sportsmen were the prime movers behind early efforts to protect and preserve this region for the desert bighorn sheep. Another group who worked hard to preserve these natural resources were local boy scouts. In 1939, 860,000 acres of desert were set aside by presidential order as the Cabesa Prieta Game Range. Work was begun to develop water resources for bighorn sheep. Shortly thereafter, World War II broke out. This remote corner of Arizona that included the Cabesa Prieta Game Range became one of the nation's most important training grounds for combat pilots. Because this training required pilots to shoot at targets on the ground and those towed behind other planes, extensive sections of the refuge were closed to the public and staff much of the time. In 1976, Congress transferred jurisdiction of the Game Range to the U.S. Fish and Wildlife Service, and the name was changed to the Cabesa Prieta National Wildlife Refuge. While the Air Force has retained the right to fly training missions over most of the refuge, the U.S. Fish and Wildlife Service manages the resources on the ground. In 1990, close to 95% of the refuge was officially designated a national wilderness. The largest wilderness area on any national wildlife refuge in the lower 48 states. As part of the National Wilderness Preservation System, the American people are guaranteed that this remote and beautiful place will remain forever wild. I was a kid. I imagined deserts to be parched, bleached, broken ground, solid rock, billowing clouds of dust, but the Sonoran Desert has taught me better than that. The soil out here is almost as precious as the rainfall that falls on it, but you'll notice that the soil is nailed down. Here we have a desert pavement, which acts as a crushed gravel mulch to hold in the soil and the moisture of the soil. And you'll notice that over here we have a cryptobiotic crust, which is actually a living organism like a skin on the desert. Cryptobiotic means hidden life, and much of the desert life is hidden, such as this soil itself. If we take a look at this piece here, this is actually a living organism. It's an alliance of algae, bacteria, and lichen, and it is alive. It's like the skin of the desert. It helps keep the dust down, keeps the soil in, retains the moisture, and if you pour water on this within an hour or so, it'll turn green. It has very few growing seasons, but it uses the most of the time it has. It is much like a skin. It's easily wounded, and it's also incredibly important for the desert. The weight of a tire will easily crush it, the turn of a tire will easily rip it, and the scars will remain for many, many lifetimes. The soil itself depends upon a number of things such as decaying leaf matter off of the creosote. When the drought comes, it drops its leaves on the ground. Also this down saguro, which is now acting as a home for lizards, for bugs, and you've got to remember, bugs fuel birds. It'll eventually decay, and this will be a very rich spot of soil here, so that eventually you'll have some other plant, hopefully another saguro, grow here someday. The Sonoran Desert is a complex ecosystem with an extraordinary diversity of plant and animal species. More species live here than any other arid region on the globe. Many have evolved ingenious strategies to survive and reproduce, despite the extremes of heat and dryness. The Cofacea Prieta refuge is at the heart of the Sonoran Desert, but this desert, our desert, is a pretty tough neighborhood. Temperature extremes running from below freezing to 130 degrees, ground temperatures 180 degrees, rainfall and very, very erratic. May range from two inches one year to ten inches the next year. And this makes for a difficult place for a plant to survive, let alone to start growth. Many of the plants have adopted forms that allow them to evade animals, which eat plants, such as the spines on this cholla. And all plants have defense mechanisms. They either taste bad or they defend themselves. Or against the weather itself, they have devices. If you come back in the summertime, this creosote bush will have dropped its green leaves, will have gone through its flowering cycle, beautiful yellow flowers and white cottony fruits. And it will be virtually brown. The creosote is very, very adept at drawing water in through its root system. And you'll notice that other plants don't grow close to creosote because this creosote is able to pull water from very, very dry soil. So it outcompetes most other plants and makes it very effective. This Akatio, for example, with its red flame-like flowers, is about to set seed, but you'll notice that it's already dropped its leaves, which were green and are now brown, and it's getting ready for the onslaught of summer. The bark is able to maintain some photosynthesis. It's a little bit green, but basically a plant goes into hibernation during the summertime. We have a nurse paloverty tree back here, which acts as the shading umbrella for saguaro seedlings, birds roost in the limbs of the paloverty, and their droppings after they've been out feasting a day on saguaro fruit, they'll drop the saguaro seeds. And because the ground is richer, the soil is more nutritious around the base of the paloverty, those seedlings have a chance. But to have that chance, they need to get the right amount of rain, that summer that they are sprouted. They need to have a good winter rain and they need to have a very good rain the following summer. You'll notice that many of the saguaroes in a certain group are about the same height, and that means that they sprouted and survived about the same time period. It may only be two, three, or four times a century that you get a good year which will sustain the saguaro crop. You seldom see an entire age echelon of saguaroes for that reason. The paloverty will eventually die before the saguaroes, partly because paloverties are shorter lived than saguaroes, but also because the saguaroes with their very, very shallow root system, anywhere from an inch to three inches below the surface, they draw in the water before the rainfall, before the paloverty has a chance to tap into it. So the saguaro receives this gift from the paloverty, but the paloverty may pay the price and they die before the saguaroes. Imagine this kind of a slope in a bumper crop year, a banner year of rainfall, and if it did, we would have lupin, a carpet of purple on this slope. We would have little onions, desert onions, bulbs below the surface that would send their flowers. The seeds could actually survive and remain viable in the soil for decades, requiring just the right amount of rainfall. There are so many unanswered questions about life in the desert. How fast do different species of plants grow? How do neighboring plants affect growth rates? How do animals and plants interact? What impact do human visitors have on wildlife and plants? As part of a long-term study to find answers to these and many more questions, permanent research plots have been established on the refuge. At regular intervals, a refuge ecologist measures the plants in the plot, notes any wildlife activities and records all observations. Photographs are also taken of the site. There are also selected monitoring areas where the long-term impact of recreational use is studied. Using GPS technology, which is based on signals from satellites, the location of plants, wildlife sightings, campsites are precisely recorded by longitude and latitude, eliminating the need for fences or markers or memory. Years from now, researchers will be able to return to the exact spot, confident that they are measuring the same plant. Another challenge is understanding how rainfall patterns influence life in the desert. What effect does a prolonged drought have? Do some areas of the refuge consistently receive less rainfall? Is there less or more rain now than 20 years ago? Since the 1960s, volunteers have provided invaluable assistance monitoring the amount and distribution of rainfall by regularly checking and recording information from as many as 50 rain gauges set up around the refuge. At a few of the more remote areas, the information on water levels is now automatically relayed by radio to headquarters. When levels are low, the refuge hauls water to fill some of the basins located strategically throughout the refuge. Many scientists believe bringing water to these basins may be critical for many mammal, bird and bat species on Cavesa. Other scientists, though, are concerned that increasing the availability of water in the desert helps support species not native to Cavesa, perhaps upsetting the natural balance. Research is underway to better understand what effect these water systems have on native species. Every few years, the refuge's bighorn sheep population is assessed by aerial surveys. The number of rams observed is used to determine bighorn sheep hunting quotas. Usually five to seven sheep hunting permits are awarded each year by lottery. Aerial surveys are also used to monitor the refuge's sonoran pronghorn antelope population, an endangered species. The U.S. Fish and Wildlife Service, as the lead agency in the recovery of endangered species, is interested in learning how much area the pronghorn use and the kinds of habitat they prefer. A number of pronghorn have been radio collared and their weekly movements tracked. Scientists are also doing research on the refuge to learn more about bats, their longevity, their migration, population trends. As the bats swoop down for insects, they are harmlessly caught in a fine mesh net. Very small identification tags are then attached to the wing. When a bat is recaptured, valuable information about its life history is revealed. Wildlife has also been studied by remote camera and by observation from blinds. Cabeza is ideal as a laboratory for those studying arid regions. Cabeza Prieta National Wildlife Refuge, managed by the U.S. Fish and Wildlife Service, is one of more than 500 refuges that make up the National Wildlife Refuge System. The mission of this incredibly diverse network of lands and waters is to conserve fish, wildlife and plant resources and the habitats they depend on for the benefit of the American people. As the 100th anniversary approaches of when the first refuge was established by President Teddy Roosevelt in 1903, we should take a moment and reflect on what a wonderful gift we have given ourselves in preserving places such as Cabeza Prieta. If we hold a globe of our planet in our hands and turn it slowly, we'll see what a special place the Cabeza Prieta National Wildlife Refuge truly is. There's no other place like it on the entire face of the earth. It is desert, sonoran desert, pristine, wild, wonderful, grand, glorious, but you probably knew that and that's the reason you're here. We have here an opportunity to take care of this desert so that it's as we saw it 100 years ago. This is a wilderness out here. Most of the Cabeza is set aside to be roadless, vehicleless, fence-less and that preserves the habitat for the wildlife itself that keeps them from being fragmented. Wilderness is much like Humpty Dumpty and once broken, difficult, impossible to ever repair to replace. We're constantly reminded out here how well nature does her job when we do not interfere. We also are able out here to study some of the great problems of our environment. We're able to ask questions and take a look at what the answers might be in a truly pristine environment, one which has not been turned over, turned upside down by our own hands. This refuge is truly our refuge, yours, mine and we can be very proud to have it, proud that we're taking such good care of it. Hundreds of generations of people have passed through this area. As it is, loved it for itself and left it in a natural way. Now it's our turn to take care of it. Taking care means be careful and be responsible. As rugged as the desert may appear, it is very fragile and easily scarred, scars which can remain a century or more. The restrictions that the refuge imposes and the advice it offers are to protect both you and the refuge. The wilderness that is Cabesa Prieta can be very dangerous, even life-threatening for the unprepared. Help can be far away if you get in trouble. So please take time to study the safety brochures and talk with refuge staff before you go out. And remember the wilderness ethic. Leave no trace of your visit.