Watch Nature Season 35 Episode 12 Online

The Sierra Nevada, a mountain range running about 400 miles along the eastern side of California and stretches into Nevada, is home to three national parks: Sequoia, Kings Canyon and Yosemite. This is a land of giants, whether speaking of trees soaring to nearly 300 feet, or massive stone monoliths far taller than any skyscraper. But the force that has given rise to the earth's largest living trees and carved out the iconic natural landmarks of the Sierras is water. The role that water has played in the creation and evolution of Yosemite Valley cannot be overstated - feeding its numerous wild rivers and countless waterfalls, and making life in this stone wilderness possible. The second force, crucial to the Giant sequoias' ability to reproduce, is fire. It is the delicate balance of these two elements, water and fire, that is vital to the continued existence of the wildlife and trees that inhabit the Sierras. Despite the recent heavy rains and snowfall, scientists are finding that water is scarcer and the threat of fire is more likely as the area continues to experience rising temperatures upsetting that important balance. Geologists, ecologists, researchers and adventurers investigate how the changing climate is affecting one of America's greatest wildernesses.