A deep valley with very steep sides or walls is called a canyon. A canyon is formed by erosion. Rivers carve canyons in the Earth when they flow through the soft rock of the canyon. The river carries away the soft rock and soil causing a large valley to form. A canyon can keep getting deeper because of the river flow.

The walls of a canyon are made of sandstone, soft rock, or granite.

A well-known canyon in the United States is the Grand Canyon. It is in the state of Arizona. The Colorado River flows through the Grand Canyon. It has been flowing through the canyon for over 60 million years! This is a huge canyon.