The Forested Rim: The grand Canyon is a giant river valley one mile deep, 280 miles long, covering 1,920 square miles, and at ts widest, reaches 18 miles rim to rim. Along the rim, Ponderosa and dwarf pinyon pines grow in the Arizona desert among cacti and yucca. Junipers support gray mistletoe berries, and Gambel oaks spread their roots to find moisture. The red tailed hawk and golden eagle soar over the forest while carpenter ants eat rooting wood. The short horned lizard eats the ants.

Lower Slopes: The changes in vegetation become apparent down in the canyon. The forest gradually changes to more stunted juniper and pinyon bushes, and cacti abound. In arid places, cacti soak up and store water. Their spines are modified leaves that retain water and keep birds from damaging the water filled cactus body. In this terrain the cacomistle, a catlike raccoon, lives in rock credvices. Porcupines are sometimes seen, and the gray fox hunts rock squirrels.

The Canyon Floor: Temperatures reach 120F in the shade on the Grand Canyon desert floor. Heat radiated from rocks keeps the night air a warm 86F. Feathery tamaricks, maidenhair ferns, and crimson monkey flowers grow along the river and creeks. Waterfalls sprouting from rock faces from gardens of green ferns and mosses that the chuckwalla, a two foot long lizard, feeds on. When frightened, it hides in a crevice, gulping air to swell up and wedge itself in tightly. Large, brightly colored lizards feed on insects. Scorpions hunt at night, stinging thier prey and sucking the juices from its body. A pink subspecies of the western rattlesnake is found only in the canyon, where its coloring conceals it against the rocks. It preys on small mammals and reptiles. The few small mammals living here emerge in the cooler night. Pocket mice, kangaroo rats, and spotted skunks find food in the rocks. Larger predators in the canyon include the lynx, coyote, wolf, and mountain lion, or puma. Mule deer and bighorn sheep eat the sparse vegetation. Flocks or various species of bird feed near the water.

How the Grand Canyon was Formed: The Colorado River formed the Grand Canyon much as a small stream washes out a gully along a muddy footpath, but it took 10 million years to do. Weather also plays a role. Water frozen in small rock cracks flakes away the stone. And lichens bite into the rock, forming soil so plant roots can crumble the rock.  But the river has had the greatest effect on the Grand Canyon's formation. It was named colorado, Spanish for "red Colored," because of the large amount of red silt it carries. This stony material has steadily scoured and gouged outer the Grand Canyon. 

Evolution at Work in the Grand Canyon: The canyon is less than six miles wide at points, but some areas span up to 18 miles from rim to rim. This enormous chasm is a barrier to many animals and has effected their evolution. For example, the Abert squirrel, with its white belly and gray tail, lives on the south side. The Kaibab squirrel, with a black belly and white tail, lives on the north rim. Apart from these differences, the squirrels are very similar. Once one species, the two squirrels can no longer inter breed because of changes in vegetation. Both species of squirrel feed on the tips of the ponderosa pine, which disappeared in the canyon during the last Ice Age. UNable to  cross the treeless canyon, the two species have become isolated of their separate rims.

About the pictures: The short haired lizard of the grand canyon is has very sharp spines. The Abert or tassel eared squirrel lives on the south canyon rim. It evolved from the same ancestor as the rare Kaibab squirrel on the north rim. The cacomistle hunts rodents and lizards by night in the canyon. This solitary mammal has changed little over the last 10 million years. Deeply eroded pinnacles and the remnants of lava flows. The Arizona chuckwalla, a plant eating lizard, basks in the canyons intense heat. High on the canyon rim carpenter ants devour a caterpillar. A sapsucker drills a tree trunk and drinks the sap leaking out. The Grand Canyon plunges to a death of 5,28 ft, more than five times the height of the Eiffel Tower (984 ft) in Paris.

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