People and Places

The Sonoran Desert is a place of great diversity, a theme that is described throughout this entire module.


Sonoran Desert Parks

Several parks exist in the Sonoran Desert to showcase the landscapes, plant and animal life, and cultural aspects of the Sonoran Desert life. Through this section, see where the parks are located, and delve into case studies of several parks and the issues that affect each in the Sonoran Desert.


Montezuma Castle National Monument - Established 1906

Montezuma Castle National Monument, located in the Verde Valley, preserves historical cliff dwellings of the Sinagua Indians, riparian habitat (near flowing or ground water), and Montezuma Well.   The five story cliff dwellings, which depict a castle, were believed to be associated with the Aztec emperor Montezuma. This historical site, however, was actually created by the Sinagua culture over six hundred years ago, which was far before Montezuma's time.   The great cliff dwellings are surrounded by limestone, which help to sustain their preservation. Montezuma Castle National Monument lies in an ecotone, where Sonoran Desert and chaparral vegetation types come together.

Visit the park online to learn more about Montezuma Castle National Monument.


Saguaro National Park - Established 1933 (East) and 1961 (West)

Saguaro National Park boasts a wide variety of plants and animals found in the Sonoran Desert, including the famous saguaro cactus.   The park is composed of two separate sections that are about 20 miles apart: Saguaro East or the Rincon Mountain District, and Saguaro West, the Tucson Mountain District.   The city of Tucson, Arizona lies between the two districts.   This park was the first national park to be set aside to protect a species of plant, namely, the saguaro cactus.  

To learn more about the park and its namesake cactus, visit Saguaro National Park online.


Tonto National Monument - Established 1907

Tonto National Monument sits on the northeastern boundary of the Sonoran Desert and is distinguished by its richly preserved cliff dwellings, which were home to the Salado culture and people.   The Salt River that runs nearby gave life to farming and tremendous plant and animal diversity; the interconnection of life that is the Sonoran Desert.

Continue to learn about Tonto in Views through the park's Virtual Experience or visit the park online at


Tuzigoot National Monument - Established 1939

Tuzigoot National Monument is an ancient village or pueblo built by the Sinagua culture.   The Sinaguas were characterized by their ability to trade products and farm the land.   Today people can visit the archeological site of the ancient pueblo and the museum with Sinagua artifacts on display. In addition, Tuzigoot includes the Tavaschi Marsh, one of the few freshwater marshes in Arizona.

Visit Tuzigoot National Monument online to learn more about this place.


Casa Grande Ruins National Monument - Established as a Federal Reserve 1892 and a National Monument in 1918

The Casa Grande Ruins National Monument was established as the nation's first archaeological reservation and is home to one of the largest prehistoric structures in North America.  The Casa Grande (or "Big House") was built approximately 700 years ago by the ancient Hohokam culture near the Gila River.  This monument is a testament to how the Sonoran Desert served as a home to ancient peoples.

Desert Sustenence

The prehistoric people we now know as the Hohokam used their environment in many ways to help them survive and flourish in the arid southwest. Unlike modern people, the Hohokam couldn’t go to the local store for supplies. Instead, they harvested what they found in the Sonoran Desert, gathering a wide variety of plants.

They gathered creosote bush and ocotillo for medicines. Cacti like the prickly pear, saguaro, cholla and hedgehog were excellent sources of food. Many parts of a cactus were eaten including the pads, flowers and fruit. Mesquite, ironwood, and paloverde trees produce edible seed pods that could be ground into flour. The Hohokam used agave plants, not only for food, but also for tools. The long strands of fibrous materials in the leaves were woven together to make twine.

The Hohokam were also hunters, using cottontails, jackrabbits, rodents, snakes, and birds as their main sources of animal protein, but larger animals such as mule deer were also eaten. The Hohokam also harvested reeds and grasses, which were plentiful along the river banks, for use in basket weaving and the construction of buildings.

As the Hohokam settled and continued to prosper in the Sonoran Desert, they built houses, towns and cities. The main component of their buildings was a caliche mud, a natural soil consisting of clay, sand, and calcium carbonate. When constructing pit houses, trees such as the mesquite were used to create a basic frame and then saguaro ribs, reeds, and grasses were added. This wood and fiber frame was covered with thick coatings of wet caliche mud, giving the Hohokam a dome shaped, thick walled structure which was well insulated from the heat of the summer.

Construction at Casa Grande Ruins was completed in a single episode around AD 1350. The Hohokam obtained approximately 600 roof beams of juniper, pine, and fir from at least 60 miles away. They laid locally available saguaro ribs and reeds perpendicular to the main beams and covered the lattice with wet mud or bundles of reeds. Still standing today, the walls of the Big House are almost four feet thick at the base and are made entirely of caliche mud, hand formed in two or three foot courses, without a wood frame. Ponderosa pine, white fir and mesquite were added for the floors and door frames. The Big House contained eleven rooms above a raised foundation constructed much like a platform mound. Its highest section, the central tier, is four stories high.

As the population grew and natural resources began to diminish, the early people had to adapt the desert to meet their growing needs. The Hohokam mastered three agricultural technologies, each used in a different environmental setting. Ak-chin farming was practiced on the alluvial fans using rainfall runoff. The term is derived from an O'odham word, ak chin, which refers to the “mouth of a wash.” Dry farming , practiced on rocky bajadas, peaked during the Classic period. Farmers used rock piles, terraces, bordered gardens, and check dams to capture rainfall runoff. But the hallmark of these agricultural technologies was canal irrigation on the rich flood plains along rivers.

The Mystery of the Big House

The Casa Grande could have been used for many things, and most likely was a central part of the Hohokam community. Modifications to the Big House suggest changes in function during approximately fifty years of use. Surplus crops may have been stored in the lower rooms, while the upper rooms may have been used for making predictions of astronomical events. They may have used this knowledge to manage the irrigation system and schedule ceremonies.

As we study these ancient people, we are reminded how critical water, food and shelter are for survival in the desert, and we begin to understand the delicate balance between consuming and protecting our natural resources.

Astronomy at the Big House

Carefully sized and placed openings in several upper-story rooms provided an unobstructed view of the horizon and sky. Compass readings from the openings indicate that the Great House occupants also could have viewed or predicted astronomical events, including solstices, equinoxes, eclipses and lunar alignments.

Some suggest that the Hohokam used the openings in the Big House walls as a calendar, which they may have used to manage their irrigation system and schedule ceremonies.

The equinox, which occurs twice a year, is a day with exactly 12 hours of light and 12 hours of dark. Alignment holes in the upper story of the Big House mark these two days of equal sunlight and darkness. As the sun is rising, the light goes through the hole in the east wall and projects a light circle on the west wall. As the sun continues to rise, the light slowly moves down the wall, eventually lining up perfectly with the hole in the west wall. Although the alignment at the Big House doesn’t always occur exactly on the days we call the equinox, it is usually within a couple of days. In 2004, the alignment in the Casa Grande occurred on March 15th, and the actual equinox was on March 20th.

Natural Resource Concerns and Research

Building a roof shelter over the Casa Grande (Big House) itself was one of the first major efforts implemented to protect the prehistoric structure from soaking rains and standing water. While providing greater protection from the elements, the roof also created a few new challenges for park resource managers.

Large populations of birds, including pigeons and house finches, use the roof shelter as protection from the direct sun and rain, as well as predatory raptors. The birds enlarge existing holes and cracks in the walls of the Big House to make nests and find shelter. They are often found pecking at the caliche, apparently attracted to the alkaline minerals it contains. The resulting bird debris attracts other pests and may cause increased erosion as it reacts with the alkali in the caliche mud walls.

The impacts of the birds and other animals on the Big House are being monitored and studied carefully. The abundant round tailed ground squirrels have been the subject of recent biological studies by University of Arizona researcher Karen Munroe. Other University of Arizona researchers, under the direction of Courtney Conway, are conducting studies of burrowing owls at the monument, another species showing increased numbers in the park.

Visitors to Casa Garnde National Monument will see a landscape that is greatly different from that which existed when the Big House was likely built. At that time, when the Hohokam lived in the area, the water table was higher, meaning there was more water available for plants and animals. As a result of development, the water table has gone down, and the trees which were once supported here have died. The landscape, which used to be a mesquite bosque, is now a creosote flat. The change in vegetation has also lead to a change in wildlife.

Learn more about Casa Grande National Monument by visiting the park's website.


Organ Pipe Cactus National Monument - Established 1937

Organ Pipe Cactus National Monument showcases the landscape and biodiversity of the Sonoran Desert.   The monument exhibits an extraordinary collection of plants of the Sonoran Desert, including the organ pipe cactus, a large cactus found only in the vicinity of the monument. in the United States. Recognizing the area as a significant portion of the Sonoran Desert ecosystem, the United Nations designated the monument as an International Biosphere Reserve in 1976, making conservation and scientific research one of its top priorities.


Organ Pipe Cactus National Monument celebrates the life and landscape of the Sonoran Desert. Here, in this desert wilderness of plants and animals and dramatic mountains and plains scenery, you can drive a lonely road, hike a backcountry trail, camp beneath a clear desert sky, or just soak in the warmth and beauty of the Southwest. The monument exhibits an extraordinary collection of Sonoran Desert plants, including the organ pipe cactus, a large cactus rarely found in the United States.

There are also many creatures that have been able to adapt themselves to extreme temperatures, intense sunlight, and little rainfall. Some of the animals found in the monument live on the edge of survival and are considered endangered. The monument shares one of the last populations of Sonoran pronghorn (Antelocapra americana sonoriensis) in the United States with the Cabeza Prieta National Wildlife Refuge and the Air Force'sBarry M. Goldwater Bombing Range. Another endangered species found in Organ Pipe is the cactus ferruginous pygmy owl (Glaucidium brasilianum cactorum) which is a tiny powerhouse of a bird, easily eating its own weight in one meal. The Quitobaquito pupfish (Cyprinodon eremus) is a shiny, blue fish that lives in one desert oasis near the Mexican border and nowhere else in the world. Organ Pipe Cactus National Monument is a haven for many migrating species including one very special species of endangered bat, the lesser long-nosed bat (Leptonycteris curasoae yerbabuenae).

The Hero of the Sonoran Desert

Although Organ Pipe Cactus National Monument has its share of insect-eating bats, our hero of the Sonoran Desert is the lesser long-nosed bat (Leptonycteris curasoae), a nectar feeding bat. Without this bat the Sonoran Desert would look much different.

The lesser long-nosed bat is found throughout southern Arizona and extreme southwestern New Mexico, through western Mexico, and south to El Salvador. With a wingspan of nearly 16 inches, this dark brown bat is one of the larger bats in North America. It has rather large eyes for its size, and small ears. This is an indication that the bat relies more upon eyesight than echolocation, although it uses both. Echolocation is a technique used by bats to navigate in the dark and find food. The bat sends out sound waves using their mouth or nose. When the sound hits an object, an echo comes back. The bat uses the echo to identify the size, shape, texture and distance of the object. Lesser long-nosed bats are nocturnal, which means they stay in caves or mines during the day and are active at night.

The lesser long-nosed bat colony in Organ Pipe is one of three large colonies in this area of the Sonoran Desert. Each is a maternity roost, occupied only by adult females. The males occupy different areas, thus minimizing competition with the pregnant females who give birth soon after their arrival. The roost itself requires complete darkness and a fairly constant, warm temperature, although the airflow requirements seem to be less stringent. For example, the roost at Organ Pipe Cactus National Monument has good airflow, but other roosts do not, which allows accumulation of gases such as ammonia. The roost is occupied only during the warmest months of the year, when warm temperatures in the mine shafts or caves keep the naked babies comfortable. The colonies range in size from 5,000 adult females in the Cabeza Prieta National Wildlife Refuge colony to 150,000 individuals in the Pinacate colony. The colony at Organ Pipe was around 10,000 individuals and has grown to around 25,000 individuals. Male bats roost in separate caves or mines, and usually in very small colonies. Each female gives birth to one baby per year, usually in late May or early June. One month after birth, the babies are ready to fly. They emerge from the roost within an hour after sunset to join the adults on a nightly journey to find food. The bats may travel as far as 40 miles to reach their feeding areas.

Lesser long-nosed bats are primarily nectar and fruit eaters, although they often supplement their diet with insects. The nectar they like best comes from columnar cacti such as saguaro and organ pipe. Both organ pipe and saguaro cactus bloom at night, perfuming the air with a heavy, sweet, musky scent. People might think the flowers stink, but it is this odor that attracts the bats. The bats are uniquely adapted to eat this nectar. They have very long noses and tongues and a wing structure that allows them to briefly hover like a hummingbird. While hovering above the blossom, the bats stick their long noses and tongues deep into the cactus flower, past the pollen and into the nectar. They take a lick, and then go on to another flower.

As they feed, the bats’ heads and shoulders become covered with pollen. When they travel from flower to flower, the bats transfer the pollen. In this manner the saguaro and organ pipe cactus are pollinated. Lesser long-nose bats are the major night pollinators of the saguaro cactus and the only pollinator of the organ pipe cactus. In mid- to late summer saguaro and organ pipe fruits begin to ripen and split open, exposing the bright red fruit. At this time, the bats then change their diet and become fruit eaters. Cactus fruit is very high in protein and carbohydrates, and provides plenty of energy for the bats.

After the bats have their first evening meal, they choose a “night roost”, a place where they feel safe from predators, where they can digest the meal, rest, and groom themselves. They will go out later and feed again near dawn, then return to the daytime roost. Night roosts are usually easy to see, as the walls of a building may be marked with yellow or red stains, direct evidence of what the bats ate for dinner!

Organ Pipe’s bats return every spring, but the population changes from year to year, and throughout the season. The numbers may be influenced by weather factors such as drought or unseasonable temperatures (either too high or too cool) or human disturbances.

Bat Research at Organ Pipe

Scientists of various disciplines use Organ Pipe Cactus National Monument to conduct important research for several reasons. The monument has long-term protection, is the geographic center of the Sonoran Desert, has valuable data that can be correlated with other research, has been free of disturbing land use such as grazing and mining for 30+ years, and has high biodiversity. Bat research has been conducted here off and on since the 1970’s and regularly since 1990. Several population monitoring programs are in place.

Some questions that researchers are trying to answer are: How many bats are found in Organ Pipe? Which species are most common, which are rare, and why? What habitats do each species use? Where do certain species roost and/or drink? What different kinds of bats are found in Organ Pipe?

The lesser long-nosed bat, in particular, is important to research because it is an endangered species, and it plays an important role in the ecosystems of southern Arizona, through interactions with saguaro and organ pipe cactus, and certain species of agave.

Continuing research will lead to better understanding of the general well-being of a species and how its habitat should be managed. Also, the research provides a more thorough understanding interactions between this bat and other species of plants and animals in the area.

One method researchers use to answer theses questions is mist netting. Mist nests look like a small volleyball or badminton net that is stretched across a water source or a roost entrance. As the bats take a drink or leave/enter the roost, they can get caught in the net. When this happens, researchers immediately go to the net and remove the bat to see what species it is.

They also record general measurements such as age, sex, general health condition. If the bat is female, they will determine whether or not she is pregnant, has recently given birth or is nursing young. In this way, researchers get a representative sampling of which bats and how many are in the area.

Another method of finding out how many bats are at Organ Pipe is video recording. While the bats emerge from the roost site at dusk to feed, a video camera, set up near the entrance to the cave or mine, records the evening outflight on infrared film. This film detects body heat and therefore does not use bright lights that could disturb the bats. The film crew also has to stay very quiet so that their presence does not disturb the bats.

Later, a researcher watches the tape in slow motion and laboriously counts the bats in each frame, adds up the numbers, and determines the population at that time. Bat colonies are usually videotaped at least twice during the summer at Organ Pipe.

The data collected gives researchers better understanding of the different species. This helps in making management decisions, such as which habitats need protection in order to preserve biodiversity.

Organ Pipe is an ideal place for lesser long-nosed bats. This is a very large protected area with suitable old mine shafts or caves for roosting. There is an abundance of columnar cacti to provide food. The area outside the monument is very sparsely populated. There are no population pressures from nearby cities. Most of the time, the only bat predators are owls or a late-flying hawk or falcon out to get an evening meal.

llegal immigration, so far, has had only a small impact on the bats, as one watering hole in the monument has become unusable due to illegal use. In one area outside the monument, illegal immigrants severely impacted a maternity colony by sheltering in the same cave where the maternity colony was located. The continuous presence of too many people, their fires, and their garbage disrupted the colony so much that the bats could no longer live in the cave and the site was then abandoned. Where the bats went is still a mystery to the scientists working in the area, but the cave was fenced to prevent human use, and the bat colony returned in 2004.

A personal account of Organn Pipe's bats from Vivian Sartori

"I waited one night to watch a bat colony emerge from an old mine tunnel.   I could hear them milling around, and, when I cautiously peeked in the tunnel I could see some of them fluttering around. Then thousands of bats came out, one after the other in a steady stream that became a torrent for the next hour. As they flew, their large, wide wings made a swooshing sound with each downbeat. The bats made their own wind, stirring the branches on a nearby tree. I watched them disappear from the twilight into the night."

Want to learn more about the bats of Organ Pipe or about the special place and it's issues? Visit Organ Pipe Cactus National Monument online.


Tumacácori National Historic Park - Established 1908

Tumacácori National Historic Park is characterized by its three ancient Spanish missions. Two of them date back to 1691, making them the oldest missions in Arizona.   Tumacácori is rich in cultural history and biological diversity partly due to its location along the upper Santa Cruz River of southern Arizona. Tumacácori National Historic Park is considered to be in an ecotone, the transition from typical desert vegetation of the Sonoran Desert region into a more mesquite scrub zone. Link to Case Study

Riparian Habitat

A riparian area is an area along a river or stream with water-loving vegetation.   Water is the key factor that influences the amount of diversity of plants and animals found there.   Riparian areas are distinctly different from the surrounding area because of available water, unique soil, and vegetation.   Riparian areas are very important because they help to naturally purify the water (filtering out pollutants in runoff) and provide food, cover, and travel corridors for wildlife in the area.

Tumacácori National Historical Park is located in the upper Santa Cruz Valley of southeastern Arizona.   It is home to three abandoned ruins of ancient Spanish colonial missions: Tumacácori, Guevavi, and Calabazas.   The Santa Cruz River flows past all three mission sites and has produced over one mile of lush riparian habitat within the Tumacácori site.

The headwaters of the Santa Cruz River are located in the San Rafael Valley in southeastern Arizona.   From there, the river heads south on a 32 mile loop through Mexico where it then begins to flow north.   The river re-enters the U.S. five miles east of Nogales, Arizona and continues to flow north-northwest until it meets up with the Gila River near Phoenix.   Many sections of the Santa Cruz River are intermittent, but the part that flows through the Tumacácori site is perennial mostly due to effluent from the Nogales International Wastewater Treatment Plant with a minor contribution from natural springs.   This ensures a year-round supply of water in the park.  

The result of this year-round supply of water is an amazingly lush and beautiful riparian habitat that contrasts greatly with the surrounding desert landscape.   Because of the rich, wet soil, tall trees grow in abundance along the river.   The Fremont cottonwood ( Populus fremontii var. wizlizenii ) and Gooding willow ( Salix gooddingii ) are two trees that grow in the gallery forest (or stream-side forest) in Tumacácori.  

Fremont Cottonwood
The Fremont cottonwood grows about 50-60 feet in height with a deep furrowed trunk about 3 feet in diameter.   The medium sized, heart-shaped leaves have flattened stems that allow them to twist in a breeze producing a soft fluttering sound.   This tree depends heavily upon a reliable water supply and has been nicknamed the "water tree."

Gooding Willow
The Gooding willow is a fast-growing, deciduous tree that attains a height of 20 to 60 feet, making it an excellent provider of browse and cover for wildlife. The bark of this tree is thick, rough, and deeply furrowed while the leaves are long slender and tapered with a length of 2 to 4 inches. It has both abundant small surface roots and a deeper main root that can reach up to 7 feet in depth. Willow shoots and bark were used by early Americans to make baskets and fish traps, and for fence posts, shelters, and firewood. Willow and cottonwood trees differ from some of the trees that grow in the more arid parts of the Sonoran Desert.   In the arid areas, trees have developed special ways to store and conserve water: very small leaves to reduce transpiration; smooth and sometimes green bark on the trunk to produce food and seal in moisture; long tap roots to reach deep water.   In riparian areas, trees are not as concerned with conserving water. Therefore, trees like cottonwood and willow, have broader leaves, rougher bark, and shallow, spreading roots.

The riparian area at Tumacácori serves as the primary water source for most of the area's wildlife species.   Many animals are drawn to this area for food and water, shade, shelter, homes, hiding places, and even to prey on the other animals that are drawn here as well.   Coyotes ( Canis latrans) , javelina ( Peccary angulatus) , zebratail lizards ( Callisaurus draconides) , roadrunners ( Geococcyx californianus) , antelope jackrabbits ( Lepus alleni) , western diamondback rattlesnakes ( Crotalus atrox) , and gray hawks ( Buteo nitidus ) are just a few of the species that are found here.

River systems in the Sonoran Desert are very important areas for migrating birds, and the riparian area at Tumacácori is no exception!   Over two hundred species of birds are estimated to live permanently in the area or use it as a migration corridor.   The riparian corridor at Tumacácori is located almost at the halfway point for birds migrating between Argentina and the Arctic, which makes it an excellent resting point.   Migratory species include black vultures ( Cathartes atratus) , summer tanager ( Piranga rubra) , and yellow-billed cuckoos ( Coccyzus americanus) , which have one of the highest nesting densities in the state.   Gila woodpeckers ( Melanerpes uropygialis ) , vermillion flycatchers ( Pyrocephalus rubinus) , curve-billed thrashers ( Toxostoma curvirostre) , red-tailed hawks ( Buteo jamaicensis) , and turkey vultures ( Cathartes aura) are just a few of the permanent dwellers in the area.  

This riparian area is also of special interest due to the large numbers of hummingbirds that migrate through the area. It is the perfect stopover place for hummingbirds to refuel in late fall when they are migrating south and in the spring when they are migrating north.   A visit to Tumacácori during one of these times is likely to be rewarded with the sight of a broad billed hummingbird ( Cynanthus latirostris ), or even one of the less common species such as the violet crowned hummingbird ( Amazilia violiceps ), the calliope hummingbird ( Stellula calliope ), blue-throated hummingbird ( Lampornis clemenciae ), or the rufous hummingbird ( Selasphorus rufus ) .  

Cultural Exchange Timeline




Pre- 1690s

Indians along the river are floodplain farming, gathering and hunting.

Late 1680s

A few Spanish ranchers and prospectors begin to move into the area.

January 1691

Indians living near present day Tumacácori invite Jesuit priest Father Kino to start a mission. He brings wheat (a year round crop), livestock, metal farming implements, and new farming techniques ( acéquia to divert water instead of relying on floodplains).

The Jesuit Order is an education order, knowledgeable in business, law, and science. Jesuit policy is to learn the native language to be able to teach their neophytes in their own tongue. They tolerate native customs that are not in conflict with Jesuit interpretation of Christian doctrine.


Spanish cattle ranchers and miners continue to move into the area. Many Indians go to work for the Spanish. The Jesuits maintain strict watch over whether or not the Spanish businessmen are treating the Indians fairly.

December 1751

After more than sixty years of living together, a relatively small number of O'odham Indians under the leadership of Luis of Saric, kill 120 Spanish and Yaqui Indians in what is known today as the Pima Revolt. One battle was fought in early January 1752 in which 43 O'odham Indians were killed. By March of that year everyone was back to living together in the missions and communities.


As a result of the Pima Revolt, the Jesuits initiate a new policy that attempts to entice the O'odham Indians to come live in the missions. New churches are built at Tumacácori, Sonoitac, and Calabazas with housing, classrooms, kitchens and other buildings for people to live in.


King of Spain expels Jesuits from all his dominions throughout the world. The Jesuits' high level of education and shrewd business abilities had gained them political enemies who convinced the king that they were going to overthrow him.


The Franciscan Order takes over in place of the Jesuits at Tumacácori. Being a "Mendicant" order and unable to own property either individually or collectively, they are less of a threat to the Spanish government. They insist that the natives learn to speak Spanish and change the Mission Indian names from their original O'odham to Spanish.


Franciscans build a new church at Tumacácori, the one that still stands today.


Spanish criollos (individuals of Spanish descent born in New Spain), unhappy with the Spanish caste system and harboring other grievances start a war for independence from Spain.


Mexico gains independence from Spain and begins expelling officials and other political office holders born in Spain from the country, including all Spanish-born priests at the missions.


Last resident Spanish priest at Tumacácori is ordered out of the country by the Mexican government.


Indians maintain the mission at Tumacácori for twenty years without a resident priest, relying on infrequent visits from priests of other areas.


Church abandoned due to Apache attacks, bad weather, war between U.S. and Mexico, and other hardships.

The River Today

The riparian area at Tumacácori National Historical Park has sustained many plant, wildlife, and human populations over the centuries and continues to be a shining example of the diversity of the Sonoran Desert. However, humans have made an interesting change.  

In 1952 the Nogales International Wastewater Treatment Plant (NIWTP) was built approximately 2 miles north of the U.S.-Mexico border in Arizona. This plant treated about 1.6 million gallons per day (MGD) of influent (wastewater flowing into the plant). The effluent (treated water flowing out of the plant) was released into Nogales Wash (a tributary of the Santa Cruz River ). In 1972, the plant was upgraded and moved to Rio Rico, Arizona, about 9 miles north of the U.S.-Mexico border, and treated 8.2 MGD of influent. By 2003 the plant was treating about 14 MGD, about 70% from Sonora, Mexico and 30% from Arizona, U.S. The effluent from this new location flows directly into the Santa Cruz River. The water is treated to the secondary level, which means that 75% of organic materials (plants, algae, and bacteria) and floating debris are removed. The plant does not remove gasoline products (fuel), metals, or ammonia and much is still unknown about how the water quality effects the natural environment.

Historically, the section of the Santa Cruz River near Tumacácori flowed much of the time, with periods of little or no flow. Early settlers at Tumacácori built acéquias , or irrigation ditches, to bring the water closer to the mission, while later settlers dug wells. Before the NIWTP expanded, the Santa Cruz River went dry around 1970 due to heavy agricultural use, stream diversions and especially groundwater pumping. Tumacácori National Historical Park includes about one mile of the Santa Cruz River, which is located approximately 1/3 mile from the cultural site. The year-round flows through the Tumacácori riparian area (about 7 MGD) are nearly 100% effluent water from the NIWTP. Without the effluent from the plant, the riparian area in the park would not continue to survive as it exists today.

Learn more about Tumacácori by visiting the park online.


El Pinacate y Gran Desierto de Altar Biosphere Reserve - Established 1993

The Pinacate Biosphere Reserve, located in the Sonoran province of Mexico near the Arizona border, was established because of its unique and diverse landscape and wildlife within the heart of the Sonoran Desert.   This reserve features a volcanic shield that includes craters, lava tubes, black pumice soil, cinder cones, and maar craters.   The Pinacate Biosphere Reserve is also home to the largest active dune field in North America.   Although areas of this reserve are extremely barren, many places support an abundant amount of plant and animal life.

The setting

The Pinacate y Gran Desierto de Altar Biosphere Reserve is located in the Sonoran province of Mexico near the Arizona border.   This area became a reserve in 1993 because of its important local biodiversity. The Pinacate Reserve is over 600 square miles and is home to 560 different plant species, 56 mammal species, 43 reptile species, 222 bird species, and 4 fish species.   It is named after the Pinacate beetle which lives in the area.   When threatened, this beetle stands on its head and emits a foul odor.   But don't let that mislead you! The Pinacate Reserve is an area of striking beauty.

Lava fields

El Pinacate is known for its one of a kind lava field.   It was created three to four million years ago by volcanic activity.   The lava field contains black pumice soil, about 400 cinder cones, and 10 massive volcanic craters called maar craters.   Maar eruptions are a rare, and occur when rising magma meets underground water.   When the magma and water meet, a chamber of highly pressurized steam is produced.   The pressure of the steam is so great that it blows an almost circular hole in the crust above.   The maar craters that remain in El Pinacate are evidence of these maar eruptions.   The largest of these craters is Cerro Elegante, which is 4,600 feet wide and 460 feet deep!

Some parts of the lava fields are very barren and moon-like, so much so that the area was used as a training ground for astronauts heading to the moon during the Apollo Space Program in the late 1960s and early 1970s. In contrast, there are many areas of El Pinacate that support a wide variety of plants and animals including creosote bush , saguaro , cholla cactus, pronghorn antelope, Gila monsters , and hummingbirds, just to name a few.   If you are lucky enough to visit in February or March, you will be rewarded with an amazing show of blooming wildflowers that contrast greatly to the black pumice soil.

A unique partnership

Organ Pipe Cactus National Monument is located in Southern Arizona just across the border from El Pinacate.   Because these protected areas are so close to each other, the staff are working together to help conserve the area.   They have developed Inventory and Monitoring programs that help identify and count different kinds of wildlife in the two areas.   This program also helps them determine if and when any animals move through wildlife corridors between the two protected areas.  

Organ Pipe Cactus National Monument and El Pinacate also collaborate to run a weather station that sits in El Pinacate. The weather station records hourly readings on rainfall, temperature, relative humidity, windspeed, wind direction, and insolation (sunlight intensity). The staffs of these two protected areas use this data to determine if the climate or weather of the area has changed over the years and how it has changed.   This data are also helpful for the Inventory and Monitoring Program of the National Park Service because it is a factor in the growth or decrease of a population of species.


Sonoran Desert Perspectives

The story is not complete, however, without the people that live here and the cultures that contribute to the Sonoran Desert's history.





Sonoran Desert

People and Places (current location)




The Sonoran Desert Index (multimedia version)

Views of the National Parks Visitor Center