Geological Evolution of
Yosemite Valley
500 million years ago
The Sierra Nevada region was submerged beneath a sea. Sediments slowly
accumulated on the ocean floor, growing thousands of feet in thickness
and compressing the lower layers into rock.
200 million years ago
Part of the Pacific plate slid under the North American plate in a
process called subduction. Deep within the earth, tremendous heat and
pressure caused the Pacific plate to melt into magma.
100 to 80 million years ago
Magma rose toward the surface and cooled underground into a huge block
of granite.
50 million years ago
The land destined to become Yosemite National Park was made up of
gentle, rolling hills and streams, including the slow-moving Merced
River. Hardwood forests flourished.
10 million years ago
Over the next 5 million years, the Sierra Nevada, California's
"backbone," rose. The Sierran block uplifted, tilting westward,
increasing the Merced River's flow so it carved the valley into a
canyon. Redwood forests flourished.
3 million years ago
The Merced River carved its canyon as much as 3,000 feet deep, while its
tributaries cut the land more slowly. Forests thinned as the Ice Age
approached.
