| The Grand Canyon is a very colorful, steep sided | | | | all of the Grand Canyon's current depth by 1.2 million |
| gorge, carved by the Colorado River, in northern | | | | years ago. The terraced walls of the canyon were |
| Arizona, USA. It is largely contained within the Grand | | | | created by differential erosion. |
| Canyon National Park which is one of the first national | | | | Lee's Ferry is considered the official beginning of |
| parks in the United States. President Theodore | | | | Grand Canyon National Park on the Colorado River |
| Roosevelt was a major proponent of the Grand | | | | and is used as a fishing area and river rafting launch |
| Canyon area, visiting on numerous occasions to hunt | | | | site. The site features several buildings built at the site |
| mountain lions and enjoy the scenery. | | | | since 1874 and a steamboat abandoned in 1913 by a |
| The Colorado River basin of which the Grand Canyon | | | | mining company's operation in the canyon walls nearby. |
| is a part has developed in the past 40 million years and | | | | The area is managed by the National Park Service |
| the Grand Canyon itself is probably less than five to | | | | within the Glen Canyon National Recreation Area as a |
| six million years old with most of the down cutting | | | | historical site. Lee's Ferry is the principle starting point |
| occurring in the last two million years. The result of all | | | | for rafting trips through the Grand Canyon, attractive |
| this erosion is one of the most complete geologic | | | | since it offers a geological travel backwards through |
| columns on the planet. Wetter conditions during ice | | | | time as the river cuts through progressively older |
| ages also increased the amount of water in the | | | | strata. The majority of trips are by dedicated |
| Colorado River drainage system. The ancestral | | | | commercial rafting enterprises that use substantial |
| Colorado River responded by cutting its channel faster | | | | motorized inflatable rafts to carry large parties of |
| and deeper. The base level and course of the | | | | tourists on the river taking up to two dozen |
| Colorado River, or its ancestral equivalent, changed 5.3 | | | | passengers per raft, with most trips lasting a week to |
| million years ago when the Gulf of California opened | | | | ten days but with some trips of several weeks that |
| and lowered the river's base level, which is its lowest | | | | travel all the way to Lake Mead, some 277 river miles |
| point. This increased the rate of erosion and cut nearly | | | | downstream. |