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Somewhere in the distance a coyote howled . . . .
Deserts don't settle down for the night, they perk up. Critters hunt in the cool evening air. Bats take flight hunting insects, and in the process, pollinate saguaro cacti. A gray fox prowls. A pack rat (also known as a wood rat) scurries about with its shiny treasure, an old Spanish gold piece perhaps dropped by Conquistadors in search of the Seven Cities of Gold. Just to the left, a rock with petroglyphs of a quadruped, snake, and lizard bears silent testimony to the long-gone Hohokam civilization. A Gila monster, one of the world's two species of poisonous lizards, lumbers about. It may be poisonous but it's hardly aggressive. Nearby, a tarantula emerges from its den--not pleasant to look upon, but also not poisonous as widely believed.
Ants leave their nest as a team to forage for themselves and their queen at an amazing rate of speed. Also depending on its speed, a kangaroo rat evades a western diamondback rattlesnake out looking for dinner. Collared peccaries (javelina) stand nearby. A black-tailed jackrabbit speeds along, zigzagging to confuse potential predators, while an elf owl watches from its nest in a saguaro cactus. And then there's that coyote.
If the Sonoran Desert is the stage, these wild critters are the cast, and the desert flora are the scenery. The arms of the saguaro (pronounced "soo-r-o") cactus stretch upward toward the sky. Its flowers stay open at night and its skin swells or contracts depending on the availability of water. Other important flora include the barrel cactus, shown in the illustration tilting toward the moon, and Englemann's prickly pear cactus, with its flat, pan-shaped leaves supporting edible, tasty red fruit that are a sign of the early summer.
Another cactus is the teddy bear cholla - interesting to look at, but don't get too close, for its spines are barbed and difficult to remove from skin or flesh. Other flora include the ocotillo, a cactuslike tree waving its red-tipped whips in the night air, as well as mesquite and Palo Verde trees situated along the arroyo. Some grasses can be found as well, the bush muhly near the fox in the illustration and prairie threeawn a little farther back.
The Sonoran ecosystem can be tough and often unforgiving. The city in the distance attests to the fact that people can and do live here. But the grave of the Buffalo Soldier shows that people can succumb to the harsh climate. Rocky soils reflect the lack of organic material. The sharp edges of the rocks confirm that erosion is often the result of the freeze/thaw cycle, which cracks rocks rather than rolling them around and smoothing their edges (as in a stream bed). And while water isn't plentiful in this environment, it does make appearances in the form of quick, violent storms that turn the normally quiet and dry arroyos into raging, torrent-filled channels.
A land that is starkly beautiful, dangerous, tempting, and fascinating - the Sonoran ecosystem.

Activity 1
The Question in Brookdale
Using this role-playing activity, students become acquainted with some of the processes used by resource agencies in making land use decisions. They consider whether a parcel of land currently managed by a natural resource agency should be made available to a local community for development purposes. The activity introduces students to the challenges resource managers face in attempting to accommodate competing demands for uses of the land while maintaining its ecological integrity.
The activity will take several days for students - preparation and two or three hours for each "public meeting."

Photo of Sonoran Desert landscape

Begin by printing the "position cards" below (one for each group of three to five students) and the background passage (one per student). Have the class read the background passage and then form small groups. Give each group a position card.
Instruct members of each group to prepare an argument for the point of view represented on their position card and consider how to present their case to the resource managers. Over the next several days, the students should conduct library research to learn how communities might have handled similar situations. For example, depending on the group they are representing, students might search for information on off-highway vehicles, personal watercraft, speedboats, or other recreational subjects, or on endangered or threatened species such as the desert tortoise or fringe-toed lizard. Students could also look for examples that specifically involve areas within or bordering the Sonoran Desert, such as the Algodones Dunes (also referred to as the Imperial Dunes) or the Colorado River.
To prepare their arguments, students may also interview city planners, staff from natural resource agencies, or other professionals engaged in resource management or land use planning to explore how they might approach the question of land use. Each group might also want to designate a spokesperson.
At the "public meeting," have the resource agency group sit in front of the class. Members of this group could be students invited from another class or representatives from each of the interest groups. Give each group five minutes in which to state its position. Students representing the resource agency can question each of the spokespersons from the interest groups.
After all groups have presented their positions, lead students in a general discussion. Make sure students see that each group does have a valid concern and that there is no "right" or "wrong" in this situation. The resource agency should decide whether or not to amend the land use plan and identify the parcel as suitable for sale to the community of Brookdale. If the students representing the resource agency determine that the parcel is not suitable for sale, ask them to propose one or more alternatives to address the community's need to expand.
After the resource agency makes its decision and/or offers its alternative(s), have students reassemble in groups made up of one person from each of the interest groups, with the exception of the resource agency. These new groups should consider the agency's alternative(s), or come up with their own alternative, and prepare to make another public presentation. In their presentations they should address how the agency's concerns, as well as those of the other various interest groups, will be addressed. Challenge each group to suggest an alternative that addresses human needs as well as the long-term health of the ecosystem.
During their discussion, encourage students to consider the following questions:

  • What else would you like to know about this ecosystem? Would it be helpful, for example, to have an inventory of the area's threatened and endangered plants and animals?
  • What are some things about the citizens and their community that would be useful to know?
  • How do the values of the various interest groups differ?
  • Does the community of Brookdale have a long-range plan that will ensure that future development is, in fact, limited to low-density development?
  • Does the availability of similar recreational and long-term visitor areas nearby affect your recommendation?
  • What is the best use of the general area in regard to human interests? What about in regard to protecting biodiversity? Are there solutions that can satisfy both?
  • What can you give up or alter about your position?
  • How would the knowledge that Indian tribes consider the Tipaza Hills significant in its entirety, and that no mitigation of the adverse impacts of development is possible, affect your recommendation?

The community of Brookdale, located along the lower Colorado River, in the Arizona portion of the Sonoran Desert, has approached the local land managing agency about acquiring a parcel of public land adjoining its town to the north. The community is interested in attracting some of the "snowbirds" - Visitors from the Northern United States and Canada - who annually migrate to Arizona and California during the winter months. The community would also like to take advantage of some of the expanding activities that are focused around the Colorado River.
The parcel that Brookdale wishes to acquire includes mostly level terrain overlooking the Colorado River, but also includes a small range of mountains that may eventually figure into the town's development plans.
Brookdale has limited opportunities for town expansion because it is surrounded along the west side by the Colorado River and on the north, east, and south by public land. As opposed to the public lands to the north of Brookdale, the lands on the east and south do not offer vistas of the Colorado River. The town's river-oriented recreational opportunities (predominately personal watercraft and speedboats) would directly compete with several other private and public facilities located on the California side of the Colorado River, as well as a long-term visitor area located on public lands approximately 32 kilometers east of the river.
The land use plan prepared many years ago, the parcel that brookdale wants to acquire was not identified as available for sale. The community of Brookdale would like the resource agency to amend the original land use plan to designate the parcel as suitable for sale. The agency will conduct a public meeting to solicit input from the various interest group who may be affected by the land use decision.
The resource agency already has on file certain information related to the parcel. Specifically, the agency has received information from numerous Indian tribes that the parcel includes an area that is of traditional cultural importance to Indian tribes in Arizona, California and Mexico. The area, known as Tipaza Hills, is valued by these groups as a spiritual retreat and a location for conducting special ceremonial activities.
Also, biologists working for the resource agency have noted that several caves located in Tipaza Hills are a critical habitat for a species of saguaro-pollinating bats. Biologists believe that an apparent decline in the number of young saguaro cacti may be attributable to a decline in the number of these bats and that an increase in insect infestation in agricultural areas farther downstream along the Colorado River may also be attributable to a decline in these bats, which also eat insects. Biologists are uncertain how widely distributed this bat species is within the Sonoran Desert, or how closely genetically related it is to other bats in the Sonoran.

Recreationists would like a broad level of high-quality recreational experiences made available at a reasonable cost and with a minimum number of restrictions. Additionally, they want the experience to be safe and family-friendly. They want

  • an attractive area to camp (with facilities such as toilets and showers) and to spend their leisure time;
  • additional recreational destinations along the Colorado River;
  • stores that sell and rent river-oriented recreational gear;
  • fresh water for drinking and outdoor swimming;
  • facilities directly accessible from the river to purchase gasoline, supplies, fresh water, and recreational equipment;
  • and specially designated areas for speedboats, personal watercraft, fishing, inner-tubing, hiking, and bird-watching.

Long-term visitors (also known as "snowbirds") are visitors from colder climates who spend the winter months in designated camping areas on public lands in Arizona and California. They want

  • hiking trails developed overlooking the Colorado River;
  • their own recreational facilities that are separate from river - oriented recreational facilities;
  • non-native trees planted for shade;
  • an outdoor pool, toilets, and fresh water;
  • and a minimum of modern developments around the long-term visitor areas.

Biologists would like to see native plants and animals protected in the wild. They want
  • minimal disruption of the existing ecosystem;
  • critical bat habitat protected;
  • a buffer area between human developments and critical plant and animal habitats;
  • the greatest possible diversity of native plants and animal species;
  • and an inventory of existing flora and fauna.
Artist's rendering of saguaro cactus

Indian tribes want unrestricted access to sacred and traditional use areas located on public lands and restrictions on access to these areas by non-Indians. They want
  • the Tipaza Hills made off limits for mineral extraction and all types of land-disturbing activities in perpetuity;
  • and access to the Tipaza Hills restricted to Indian tribes to protect the sacred mountains.
Artist's rendering of desert landscape

Farmers are concerned about the effects of federal actions on the productivity of privately owned farmlands and the availability of water for irrigation downstream form public lands. They want
  • insect - eating animals protected;
  • and upstream use of water from underground aquifers limited.


Artist's rendering of lesser longnose bat

Members of the Brookdale Chamber of Commerce want

  • the federal parcel of land acquired for low-density developments;
  • some level of economic growth promoted without significantly changing the "smalltown" character of their town;
  • long-term visitors who will spend money but only stay part of the year;
  • and a limited level of development to accommodate thelong-term visitor.

Activity 2
Waxy Leaves
Desert plants known as drought resisters include a variety of shrubs and other woody or fibrous plants. These plants can take the worst the desert has to offer. Cacti store moisture in their spongy stems or root tissues during periods of rain, then use it sparingly during times of drought. Other plants, such as the catclaw, the acacia, and the mesquite, have deep and widespread root systems to capture all available moisture.
Many drought resisters, such as the creosote bush, have tiny leaves and/or coat their leaves with a waxy, resinous substance to reduce moisture loss. The following activity illustrates how one of these adaptations ("waxy" leaves) prevents water vapor from escaping from a plant, allowing the plant to retain its moisture for use during hot, dry periods.

For each group of students, you will need two plastic bags, two potted seedlings, petroleum jelly, adhesive labels, a measuring cup, and water.

Artist's rendering of potted plants in plastic bags

Instruct the students to add the same amount of water to both plants. Have them label one plastic bag "petroleum jelly" and the other bag "no petroleum jelly."
Students should place one seedling in the bag labeled "no petroleum jelly," seal the bag, and put it in a sunny window. Next, they should rub petroleum jelly on the bottom of all the leaves of the second plant, put this seedling in the other bag, seal the bag, and place it next to the first plant.
Wait several hours or overnight, then ask students to observe the bags and identify if either bag has water droplets collected on the sides. Discuss the following questions with students:

  • Where does the water comes from? (It condenses from water vapor that passes out of the plant. The loss of water vapor through the stomata of a leaf is called transpiration.)
  • What does the petroleum jelly prevent from happening? (It prevents water vapor from escaping from the plant.)

Liken the loss of water from the plant with petroleum jelly on its leaves to the creosote bush and other desert plants that have waxy leaves.

Traces of Prehistoric Peoples
Several prehistoric cultures occupied the Sonoran Desert after the Clovis people. People we call the Hohokam lived in the Salt, Gila, and Santa Cruz River basins of south-central Arizona from about 2,000 years ago to the beginning of the fifteenth century. The Hohokam are noted for the extensive network of canals they built to irrigate their fields of corn, beans, and squash. Archaeologists have found the remains of over 1,100 kilometers of Hohokam irrigation canals in the Phoenix Basin. Irrigation helped the Hohokam maintain a highly complex and sophisticated culture. They built large mounds in their villages; made beautiful textiles, shell jewelry, and pottery; and traded with groups as far away as the California coast, the Great Plains, the Rocky Mountains, and Mesoamerica. By the time Europeans arrived in the late seventeenth Century, the Hohokam culture seemed to have vanished, but many people believe the present-day Piman tribes of southern Arizona are the descendants of the ancient Hohokam.

Painted rock petroglyphs
Painted rock petroglyphs - Photo by Gary Stumpf

Among the most fascinating of evidence left by prehistoric inhabitants of the Sonoran Desert are petroglyphs or rock carvings. Petroglyphs are the result of chipping, pecking, rubbing, drilling, or scratching of a rock surface. Petroglyphs are often found on rock surfaces coated with "desert varnish" of iron- and manganese-oxides and other minerals. Such petroglyphs can be seen in contrast to the background rock because they have been formed by the removal of surface patina. In some instances, the exposed surface has had sufficient time and the conditions have been right for repatination to occur.

Casa Grande in 1891
1891 photograph of Casa Grande

Evidence suggests that one purpose of rock art - perhaps the principal purpose or function -was religious, having to do with sacred ceremony. Record-keeping, decoration, and doodling also seem to have been purposes.
The term intaglio (in-tal-yo) is taken from a printmaking process. Intaglios are usually engraved or incised on desert pavement terraces. These terraces are created by a complex process of water and wind. Rock materials were transported by ancient rivers and streams, then deposited in graded layers of coarse cobbles, gravels, and finer materials. Thousands of years of erosional forces eventually remove the finer materials, leaving a coarse, densely packed, level desert pavement behind. These cobbles and gravels are then slowly covered with layers of ferro-manganese deposits and colonies of microscopic organisms. Through the years, the stones develop a glossy patina that appears black from a distance. To create an intaglio, the large rocks are moved away and the small cobbles are scraped back to expose the lighter soils underneath, thus creating an image.

Fisherman intaglio, which was incised or engraved on desert pavement terrace
"Fisherman" intaglio - Photo by Harry Casey

There is no absolute or conclusive way to date intaglios. Archaeologists' estimates of intaglio ages range from 10,000 years ago to the present. Intaglios can be ruined unintentionally by someone unaware of their existence or, more frequently, by vandals intentionally driving over the figures, senselessly scarring or obliterating them forever.

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Last updated: 11-13-2009