Illustration of the valleys of the Sierra Nevada mountain range (right) formed by the action of glaciers three million years ago (left). During that period, the glaciers moved downhill through existing channels eroded by streams and rivers. The heavy weight of the ice carved out the sides of the winding V-shaped river valleys into straight, U-shaped valleys. When the glaciers melted, they left behind wide broad valleys with very steep granite walls. Typical examples are Yosemite Valley and Kings Canyon, the latter in Sequoia and Kings Canyon National Parks, California, USA. For the separate landscapes, see C028/6532 and C028/6533.