(click here for a powerpoint slide show)

470 – 220 million years ago:

Layered sediments covered the sea floor west of the North American continent.

220 – 80 million years ago:

Masses of molten magma rose from deep in the earth, pushing the layers of sediment up into mountains and breaking through as volcanoes.

80 – 25 million years ago:

Uplift and erosion stripped away most of the sedimentary layers, leaving the cooled magma (granite) exposed.

25 million years ago:

Rolling hills and valleys covered the current Yosemite area, the Merced river flowed through a shallow valley.

25 to 10 million years ago:

The mountains were pushed up higher from an increase in activity below the earth’s surface, causing the Merced river to dig deeper (erode) into its valley.

10 – 2 million years ago:

The land continued to push up, the water continued to erode down. The V-shaped valley got deeper.

2 million years ago:

An ice age occurred. Glaciers from the highest parts of the Sierra Nevada grew so big that they flowed down through Yosemite Valley, widening and cutting the Merced river’s path.

20,000 years ago:

The glaciers melted out of Yosemite Valley.

10,000 years ago:

The glaciers melted and created Lake Yosemite, which filled the Valley. But the Merced river and small creeks were filling the lake with sediment…

Today:

The sediment eventually filled Lake Yosemite and turned it into the meadows and forests of today.