Yosemite is still rising: the geology of granite and ice

Yosemite is still getting taller. The Sierra Nevada is rising at Mount Dana by about 4 centimetres (1.5 inches) every hundred years, faster than erosion is wearing it down, so the range is gaining height. The cliffs, domes and waterfalls that made Yosemite a national park are the product of two forces that are both still at work: a mountain range lifting and tilting, and ice carving what the lift exposed.

Granite, lifted and tilted

The park's rock is mostly granite, with remnants of older rock around it. About 10 million years ago the Sierra Nevada was uplifted and tilted: the western slope, where Yosemite lies, became long and gentle, and the eastern slope steep and dramatic. Tilting a landscape steepens its rivers, and the steeper rivers cut deep, narrow canyons into the rising block.

Several of the largest exposed granite monoliths on Earth are in Yosemite Valley — Half Dome, El Capitan, Sentinel Rock — and the highest peaks, Mount Lyell, Mount Dana and Kuna Peak, rise above 3,960 metres (13,000 feet).

Then the ice

About a million years ago snow and ice began to build up at high elevations and flow down the river canyons as glaciers. In Yosemite Valley the ice may have been 4,000 feet thick during the early glacial episode. Where a river cuts a V, a glacier grinds a U, and the valley visitors come to see is that U.

It was this scenery — glaciers working on granite — that was the reason the park was preserved.

What is still changing

Besides the uplift, rockfalls keep reshaping the valley walls, rivers go on deepening the valley floors, sediment slowly fills alpine lakes, and the small cirque glaciers that remain, though melting fast, still scour bedrock and push material onto their moraines.

The park itself spans roughly three-quarters of a million acres across Madera, Mariposa and Tuolumne counties. It was established on October 1, 1890; more than 94 percent of it is designated wilderness, 135 miles of the Tuolumne and Merced rivers are national wild and scenic rivers, and it has been a UNESCO World Heritage Site since October 31, 1984.

Sources

Written from the National Park Service's NPS Geodiversity Atlas — Yosemite National Park, California, a work of the United States government in the public domain, drawing on the park's Geologic Resources Inventory, Anderson (2017) and Huber (1989).