Yosemite Geology

For 500 million years, the geological history of Yosemite has been evolving from an ocean floor to gentle, rolling hills to the formation of the steep Sierra Nevada mountain range with deep river canyons. Three million years ago, the Ice Ages brought glaciers that scraped and carved the valleys and canyons with such force that the remaining granite still shows the direction of glacial movement. When the last glacier finally melted approximately 10,000 years ago, rock debris dammed the valley and created Lake Yosemite. Tributary creeks plummeted off sheer cliffs and gave birth to the Park's famed waterfalls. Sediment continued to fill the lake through natural processes until it eventually formed the present valley floor.  Yosemite's geological evolution continues today as Mirror Lake slowly fills with sediment as Lake Yosemite did. In 1996, the Happy Isles rockfall sent 80,000 tons of rock to the valley floor at 160 mph, proof that powerful forces are still at work. From every vantage point in Yosemite there are breathtaking mountains, waterfalls, meadows and forests. Galen Clark, known as the "Guardian of Yosemite" for 20 years, proclaimed it the "grandest of all God's temples."