Geology of Yosemite National Park
The creation of a dramatic landscape of extremes on the scale of Yosemite National Park doesn’t happen overnight you know, it takes years – millions of years.
The landscape at Yosemite is glaciated, the scenery was largely sculpted by glaciers and their underlying rocks (which is part of the reason why this was chosen to be a National Park in the first place). This park is packed with many of the most photographed landmarks in the world – Yosemite Valley, Yosemite Falls, Nevada Falls, Bridalveil Falls, Half Dome . . . the list goes on. Glaciers can form many different landforms including jagged peaks, rounded domes, U-shaped canyons, moraines and, of course, the world famous waterfalls of Yosemite National Park.
Starting with volcanic and plutonic activity some 210 million years ago was the creation of the Sierra Nevada Batholith – made up of mostly granite rocks from around 7 miles beneath the surface of the earth. This carried on throughout the Cretaceous period (around 80 million years ago) and then 20 million years ago a range of (now extinct) volcanoes from the Cascade Range added their might to the eruptions. This is what blasted the area to the north of Yosemite.
Around 10 million years ago (wow, we’ve skipped 200 million years in one paragraph – not bad eh) – vertical movement started along the Sierra fault uplifting the Sierra Nevada. What with all of the uplifting and tilting the streams ran at an ever increasing speed cutting their way down the valleys faster and faster. More uplift followed by tons more erosion – then the glaciers arrived carving their way through the valley floors.
Glaciers sculpted the region for a couple of million years – there were at least four glaciations during this period – Sherwin, Tahoe, Tenaya and Tioga.
The longest glacial river in Yosemite National Park ran for 60 miles down the Grand Canyon of the Tuolumne River passing further than Hetchy Hetchy Valley. The only areas of the park which were not covered by glaciers were the very highest peaks of Mount Conness and Mount Dana.
As the glaciers retreated so lakes were formed by the recessional moraines – a great example of this is Lake Yosemite which covers much of the Yosemite Valley floor from time to time.