The Grand Canyon

Carved over millions of years by the powerful Colorado River, the Grand Canyon spans miles. One miledeep, hot and arid for much of its length, the canyon contains a variety of plants and animals.

The forested rim

The Grand Canyon is a giant river calley one mile deep, 280 miles long, covering 1,920 square miles, and its wildest 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 fray misletoe 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 rotting wood. The shorthorned lizard eats the ants.

Lower slopes

The changes in cegetation become apparent down in the canyon. The forest gradually juniper and pinyon bushes, and cacti abound.

In arid places, cacti soak up and store water. Their spinesare modified leaves that retain water and keep birds from damaging the body. In this terrin the cacomisle, a cat-like raccoon, lived in rock crevices. Porcupines are sometimes seen, and the gray fox hunts rock squirrels.

The canyon floor

Temperature reach 120 F in the shade on the Grand Canyon's desert floor. Heat radiated air a warm 86 F.

Feathery tamarisks, maidenhair ferns, and crimson monkey flowers grow along the river and creeks. Waterfalls spouting from rock faces from gardens of green ferns and mosses that the chuckwalla, a two-foot-long lizard, feed 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 their prey and sucking the juicies 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 repties.

The few small mammals living here emerge in the cooler night. Pocket mice, kangaroo rats, adn spooed skunks find food in the rocks. Larger predators in the canyo include the lynx, coyote, wolf, and mountain lion, or puma. Mule deer and bighorn sheep eat the sparse vegetation.

How the grand canyon was formed

The Colordo river formed the Grand Canyon much as a small steam 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 craks 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 Cnayon's formation. It was named colordo, Spaninsh for "red colored" because of the large amount of red silt it carries. This stony material has steadily scoured and gouged ou the Grand Canyon.

Evolution at work in the grand canyon

The canyon is less than size 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 nad has affected their evolution.

For example, the Abert squirrel, with its white belly and gray tail, lives on the south side. The kailbab squirrel, with a black belly and white tail, lives on the north rim. Apart from these differences, the squirrels are cery similar.

Once one species, the two squirrels can no longer interbreed because of changes in vegetation. Both species of squirrel feed in the tips of the ponderosa pine, which disappeared in the canyon durign the last Ice Age. Unable to cross the treeless canyon, the two species have become isolated on their separate rims.