Standing on the rim of the Grand Canyon, gazing across this giant wound in the Earth’s surface, a visitor might assume that the events that produced the canyon, far from being sudden and cataclysmic, simply add up to the slow and orderly process of erosion.
Many millions of years ago the Colorado Plateau in the Grand Canyon area contained 10,000 more feet of rock than it does today and was relatively level. The additional material consisted of some 14 layered formations of rock. In the Grand Canyon region these layers were largely worn away over the course of millions of years.
Approximately 65 million years ago the plateau’s flat surface in the Grand Canyon area bulged upward from internal pressure; geologists refer to this bulging action as upwarping; it was followed by a general elevation of the whole Colorado Plateau. a process that is still going on. As the plateau gradually rose, shallow rivers that meandered across it began to run more swiftly and cut more definite courses. One of these rivers, located east of the upwarp, was the ancestor of the Colorado. Another river system called the Hualapai, flowing west of the upwarp, extended itself eastward by cutting back into the upwarp; it eventually connected with the ancient Colorado and captured its waters. The new river then began to carve out the 277-mile-long trench that eventually became the Grand Canyon. Geologists estimate that this initial cutting action began no earlier than 10 million years ago.
Since then, the canyon forming has been cumulative. To the erosive force of the river itself have been added other factors. Heat and cold, rain and snow. along with the varying resistance of the rocks, increase the opportunities for erosion. The canyon walls crumble; the river acquires a cutting tool, tons of debris; rainfall running off the high plateau creates feeder streams that carve side canyons. Pushing slowly backward into the plateau, the side canyons expose new rocks, and the pattern of erosion continues.
Which of the following conclusions about the Grand Canyon can be drawn from the passage

As the 21st century begins, a number of leaders in politics, education, and other professions believe that the United States must adopt some new values to go along the older traditional ones. What new values should Americans adopt This is a very difficult question to answer. Certainly, a greater value should be placed on the conservation of natural sources; Americans should learn to use less and waste less. But conservation has never been a strong value to Americans, who have believed that their country offered an endless, abundant supply of natural resources. Recently, progress has been made--more and more Americans are recycling their paper, cans, bottles, and other goods--but old wasteful habits die hard. Furthermore, their need to protect the environment may conflict with the need for job, as in the Northwest, where conservationists battle lumber companies that want to cut down ancient redwood trees. A belief in the value of conservation is still weak compared with other American values; it can become stronger only as Americans see the need for it more clearly.
In addition, Americans may need to place a stronger value on cooperation on a national scale to achieve important national objective. The American idea of the national good has never been based on national cooperation but rather on the freedom of the individual, maintaining those conditions that provide the greatest freedom and prosperity for the individual. It is far more difficult for Americans to accept shared sacrifice for the common good and well-being of the entire country. For example, although the majority of Americans believe that is extremely important to balance the national budget and reduce the deficit, they do not want to see cuts in government programs that benefit them personally.
The American value of competition also hinders the development of a spirit of national cooperation. Competition sometimes encourages feelings of suspicion rather than the mutual trust that is necessary for successful national Cooperation. Although Americans often cooperate successfully on the local level--in neighborhood groups and churches, for example they become suspicious when the national government becomes involved. For example, on the national level, they may see themselves as part of an interest group that is competing with other interest groups for government funds. A request by the national government for shared sacrifice may be seen as coercive and destructive rather than voluntary and constructive. However, the demands of the 21st century may compel Americans to place a greater value on national cooperation to solve problems that affect them all, directly or indirectly

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