The Kaibab-Coconino Plateau

As the Paleozoic Era gave way to the Mesozoic, some 225 million years ago (MYA), an ovoid upwarping of Earth's crust developed in what is now northern Arizona.  Reinforced during the Laramide Orogeny (the formation of the Rockies, 70 MYA), this broad ridge was eventually covered by layers of Mesozoic and Tertiary sediments (both erosional and volcanic).  Late in the Tertiary Period, the Miocene-Pliocene Uplift (stretching from about 15-5 MYA) lifted the entire Colorado Plateau and its rim of mountain ranges another 5000 feet, increasing stream erosion across the Province.  Rising on the west side of the Continental Divide, the Colorado River flowed westward and gradually southward to enter the Sea of Cortez; en route, it crossed northern Arizona, entrenched in the younger sediments that covered the Kaibab-Coconino ridge.  As the Colorado Plateau rose beneath it, the river was forced to cut down through this ridge of Paleozoic rock (and the upper layer of the ancient Precambrian basement that lies beneath it).  Augmented by the wet climate of the Pleistocene (2 to 0.01 MYA), the Colorado thereby sculpted the Grand Canyon, the most spectacular chasm on our planet.

The ridge itself, oriented NNW to SSE, has since been uncovered by erosion.  Streams from its eastern edge drain directly into the Colorado (or into the Little Colorado south of the Grand Canyon), while its northwest flank drains to the Colorado via Kaibab Creek and its southwest flank feeds the Cataract River, another tributary of the Colorado.  The exposed ridge is composed primarily of Kaibab limestone overlying Coconino sandstone; that portion north of the Grand Canyon is known as the Kaibab Plateau while its segment south of the Canyon is referred to as the Coconino Plateau.  The rock strata of the plateau, deposited during the Permian Period, form the upper layers of the Grand Canyon

The Kaibab Plateau rises to elevations that exceed 9200 feet, supporting a rich forest of fir, spruce and aspen, giving way to ponderosa pine and then pinon-juniper woodlands at lower elevations.  The Coconino Plateau is 7400 feet above sea level at the south rim of the Grand Canyon and gradually lowers toward the west, south and east; it is covered primarily by ponderosa pine parklands.  South of the Coconino Plateau, the landscape is dominated by the high peaks and scattered cones of the San Francisco Volcanic Field, including Humphreys Peak (12,633 feet), the highest point in Arizona.

Musk Hogs

Collared peccaries, otherwise known as javelinas or by their more colorful title of musk hogs, are native pig-like residents of the Sonoran and Chihuahuan Deserts of the Southwest U.S., from southern Arizona to southwest Texas. They and other peccary species are also found southward through Mexico, Central American and most of South America. All are descendents of a Eurasian ancestor that split from the common pig lineage back in the Eocene, some 50 million years ago.

Living in herds of up to 50 individuals (10-20 is typical), collared peccaries roam the canyons and arroyos of the Desert Southwest, under the control of a dominant male. He breeds with females in the group throughout the year and pregnant females temporarily leave the herd to deliver their young (usually 2) in a den or hollow log. Older sisters help to raise their new siblings and newborn females are sexually mature within a year.

Thinner and longer-legged than common pigs, collared peccaries have a coarse coat of gray-brown hair with a darker mane down their back and a lighter ring around their neck; while their eyesight is rather poor, these desert residents have a keen sense of smell. Short, sharp tusks offer some protection from predators (mountain lions, coyotes, bobcats) but their aggressive nature and group mentality provide their best defence. Omnivorous, peccaries feed on a variety of plant materials (prickly pear cactus and agaves are favored) but also consume eggs, reptiles and carrion; avoiding the heat of mid-day, they usually forage in the early morning and evening hours. The name "musk hog" is derived from the potent musk gland on their upper rump which they use to mark their territory and one another.

The Desert Raccoon

Natives of Central and South America, coatimundis have spread into the Sonoran and Chihuahuan Deserts of the southwestern U.S. Formally known as white-nosed coatimundis, these members of the raccoon family, unlike their more widespread and familiar relatives, are diurnal and gregarious, often moving about in noisy bands composed of females and their young.

Adult males, twice as large as the females, weigh up to 25 pounds and tend to be more solitary. Mating occurs in the early spring and 4-6 young are born after a gestation of almost 3 months. Females often use rock crevices for nursery dens but she and her offspring later use crude arboreal platforms for sleeping and resting. Wandering about for much of the day, these omnivores locate food and prey with their long, tapered snout; insects, lizards, eggs, nuts and fruit comprise most of their diet. Coatimundis are agile climbers, equipped with sharp claws to grasp limbs and a long tail for balance.

Favoring wooded canyons of the Desert Southwest, white-nosed coatis and their brown-nosed South American cousins are threatened primarily by habitat loss. Natural predators include mountain lions, coyotes, bobcats and golden eagles in the U.S. and jaguars, ocelots and boas in Central and South America. Known to live up to 15 years in captivity, coatis have a natural life span of 6-8 years.

Kofa NWR

If you enjoy an escape to the Desert Southwest during the winter months but hope to avoid the congestion of large cities and National Parks, consider a visit to Kofa National Wildlife Refuge, northeast of Yuma, Arizona. This extensive preserve (over 665,000 acres) was set aside in 1939 to protect habitat for desert bighorn sheep; more than 80% of the refuge is designated wilderness and it thus harbors some of the most pristine Sonoran Desert landscape in the U.S.

Stretching between the Kofa Mountains on the north to the Castle Dome Mountains in the south, this refuge is accessed by a network of graveled roads, most of which require four-wheel drive vehicles. However, the road to Palm Canyon, leading east from US 95 between Quartzite and Yuma, can be traversed by the family car and is perhaps the best means to explore this ecosystem; a short trail at its terminus leads to a stand of California fan palms and conditioned hikers can proceed on to higher terrain.

In addition to the fan palms, the only palms native to Arizona, Kofa NWR is known for its tremendous diversity of Sonoran Desert plants, including the Kofa mountain barberry. Of course, the refuge is also home to a spectacular variety of desert wildlife; joining the reclusive desert bighorn sheep are mountain lions, coyotes, mule deer, kangaroo rats, five species of rattlesnake, a diverse collection of lizards and the usual mix of Sonoran desert birds. Named for the abandoned King of Arizona gold mine, this wilderness also harbors remnants of past mining and ranching activity; since it was used for military training during WWII, it may contain unexploded ordinance and visitors are cautioned not to handle such materials.

The Desert Owl

Elf owls, the smallest owls in North America, are summer residents of the Sonoran Desert in southern Arizona; some inhabit the Chihuahuan Desert of southernmost New Mexico while others breed in dry country along the Rio Grande River of southern Texas. Less than six inches tall, these tiny raptors are best identified by their yellow eyes, white eyebrows and round, tuftless head.

Calling from a potential nest cavity in April, the male attracts his mate and both parents incubate the eggs (usually 2-4) for several weeks. Nest cavities, always more than ten feet from the ground, are abandoned woodpecker holes in saguaro cacti or in sycamores along streams near the base of mountain ranges; gila woodpeckers usually sculpt the saguaro cavities while flickers and acorn woodpeckers provide those in riparian areas. Strictly nocturnal, elf owls feed primarily on flying insects but may grab a scorpion or ground beetle; during the breeding season, they are often active at dusk but are otherwise best observed within their cavity during the daylight hours.

Relying on a diet of insects, these small owls migrate southward into Mexico for the winter, when chilly nights eliminate their prey in the Desert Southwest. Since they inhabit arid landscape with few larger owls, roost in cavities far from the ground and capture their meals in mid-air, elf owls have few natural predators and may live up to six years in the wild.

Madera Canyon

The mountain ranges of southeast Arizona offer steppingstones of forest for birds migrating between the Sierra Madres of Mexico and the Rocky Mountains of western North America. In addition, these sky islands provide cool, moist retreats for the birds and other wildife that reside in the Sonoran Desert, concentrating their populations and making them more accessible to humans who hope to observe them. Harboring a mix of Mexican and North American species, these ranges are thus renowned as superb birdwatching sites and Madera Canyon is among the more popular destinations.

Incising the northwest flank of the Santa Rita Mountains, 25 miles SSE of Tucson, Madera Creek rises along the crest of the range (an elevation of almost 9500 feet) and drops 7000 feet to the floor of the desert. Within its spectacular canyon, varied life zones attract a tremendous diversity of plant and animal life, including more than 200 species of resident and migrant birds. Among the more treasured sightings are elegant trogons, sulfur-bellied flycatchers, painted redstarts, yellow-eyed juncos, flame-colored tanagers, whiskered screech owls and 15 species of hummingbirds; the latter are best observed at feeding stations around the Santa Rita Lodge. Other canyon residents include black bears, mountain lions, bobcats, coati, ring-tailed cats, wild turkeys, black-necked garter snakes, tiger rattlesnakes and canyon tree frogs.

Accessed by a central roadway and numerous trails, Madera Canyon is a popular site for hiking and camping throughout the year; day use and camping fees are charged. Madera Creek, which sculpted this magnificent canyon, generally flows from the monsoon season of mid-late summer until depletion of the snow pack in early spring but can be dry for months at a time. Birders are advised to avoid the weekend crowds and to visit the Canyon early or late in the day.

The Nature of Wildfire

The massive wildfire that is ravaging northeast Arizona is surely causing hardship for many humans and its scar will stretch across the landscape for many years to come. But wildfires, like floods, hurricanes and other weather-related "disasters" have been essential to the health of natural ecosystems throughout the history of our planet.

Usually triggered by lightening and fueled by drought, wildfires serve to clean out our forests, recycle nutrients and protect our prairies. For many plants, as with lodgepole pines, wildfire is an essential factor in the reproductive cycle, releasing seeds and setting the stage for germination. Furthermore, fire removes invading, alien plants that are unable to withstand its effects, clearing the landscape for native species.

While a large number of creatures may succumb to wildfire, most animals that live in fire-prone ecosystems adapt to these seasonal events, escaping the flames within burrows or using their natural skills to flee the torrent. Humans, on the other hand, tied to their plot of earth, are at the mercy of wildfires and often lose their homes and possessions; the choice to live amidst the natural beauty of fire-born ecosystems comes with a price.

The Virgin River Staircase

The North and East Forks of the Virgin River rise on the south face of the Markagunt Plateau, in southwest Utah, amidst colorful outcrops of the Claron Formation. From these early Tertiary sediments, the tributaries begin to flow back in time, entering Zion National Park through Cretaceous Dakota Sandstone before carving magnificent canyons of Jurassic Navajo Sandstone; the North Fork has produced the more famous Zion Canyon while the East Fork sculpted Parunaweep Canyon.

The Forks join west of Zion, where the Virgin River begins a journey across Triassic redbeds, interrupted by Quaternary basalt flows along the Hurricane Fault. Beyond St. George, the river dips into the northwest corner of Arizona, where it has carved the spectacular Virgin River Gorge through Permian limestone and older, metamorphosed Paleozoic strata. West of the Grand Wash Fault, which marks the west edge of the Colorado Plateau, the canyon widens and the river enters the stark landscape of the Mojave Desert. After flowing into Nevada, the Virgin River curves to the south and joins the Colorado River within Lake Mead.

Western rivers are appealing to the naturalist in many ways. Producing ribbons of vegetation through arid landscapes, they also reveal the complex geology that underlies and explains the rugged, surface topography. Though relatively short, the Virgin River of Utah-Arizona-Nevada has bestowed its gifts in spectacular fashion.

Hualapai Crossroads

Just southeast of Kingman, Arizona, the scenic Hualapai Mountains form a high wall above the east edge of the Colorado River Valley. Like most of the ranges in the Basin & Range Province, it is a fault-block uplift, aligned from north to south, the product of stretch and fracture within the Earth's crust.

The most interesting feature of the Hualapai Range, however, is its location at the crossroads of several geophysical provinces. To its east, beyond the Big Sandy River Valley, is the western wall of the Colorado Plateau, which extends across northern and eastern Arizona, southeastern Utah, northwest New Mexico and western Colorado. The Hualapai Mountains, themselves, lie within the southernmost extension of the Mojave Desert while, to their south and southwest, the terrain drops into the Sonoran Desert of southeast California, southern Arizona and northwest Mexico.

For now, the Hualapai Range towers above the stark, arid landscape of northwest Arizona, offering a cool escape for wildlife and humans alike. Eventually, as rifting continues across the Great Basin, the ocean will invade through the lower Colorado Valley and these mountains, like other ranges of the Intermountain West, will overlook a vast inland sea.

Evolution of the Sonoran Desert

The Sonoran Desert of the Southwest U.S. and Northwest Mexico is a product of its latitude, the global climate and the regional topography. Lying along one of the desert bands (which run just north and just south of the Tropics), this arid ecosystem receives copious sunshine and is subjected to prolonged periods of high pressure, below which the air is sinking. This atmospheric condition retards cloud formation and both warms and dries the air as it plummets toward the Earth's surface.

Covering a broad basin and surrounded by highlands, the Sonoran Desert is shielded from moisture in all directions; to the northwest are the Sierra Nevada Mountains and the high Mojave Desert, to the north and east is the Mogollon Rim of the Colorado Plateau, to the southeast is the wall of the Sierra Madre Range and, to the southwest, are the mountains of Southern California and the Baja Peninsula. Any air that enters the Sonoran is thus downsloping from higher terrain, causing it to heat up and dry out even further. Since the mountains and plateaus that surround it were uplifted within the past 4 to 20 million years (during the Miocene and Pliocene), the Sonoran Desert is one of the youngest ecosystems on our planet.

Throughout the Pleistocene and into the Holocene, Earth's climate has undergone dramatic shifts. When the climate cooled and glaciers advanced, the area of the Sonoran Desert decreased; in contrast, when the climate warmed (as it has done over the past 10,000 years), the Desert advanced, climbing onto the walls of the adjacent highlands. Throughout these gyrations, the regional flora and fauna have evolved, developing traits that enhanced survival in an arid environment with intense sunshine, cool nights and seasonal rains.