About six million years ago, the Colorado plateau in the south-western USA was a flat coastal plain. Winding slowly across it was the Colorado River. Gradually, earth movements pushed the plain upwards, making the river run faster and faster. The force of the flow began wearing out the Grand Canyon.
This, the world’s largest gorge, is 446 km (277 miles) long and 1.6 km (1 mile) deep in places. Exposed on the canyon walls are layers of rock, the oldest at the bottom being about 2,000 million tears in age. Resting on them are younger and younger rocks. In some ways, climbing up or down the canyon and past the rocks from different periods is like a journey through time.