Toward the end of Earth’s last ice age, huge glaciers moved down from the Sierra Nevada high country carrying debris that scoured and polished Yosemite’s granite rocks to a smooth surface.
Of all of the stunning natural features that compose Yosemite’s landscape – including gushing waterfalls, skyscraping mountain peaks, alpine lakes, and giant sequoia groves – the park’s granite domes are among the most unique.
Half Dome is the most famous, prompting curious visitors who stare up at the giant dome from the valley floor, or capture it in photos from Glacier Point, to ask: how were domes like this made?
Part of the answer lies with ancient glaciers. Toward the end of Earth’s last ice age (approximately 10,000 to 15,000 years ago), huge glaciers moved down from the Sierra Nevada high country, following river canyons and valleys. Along the way, the glaciers carried with them fields of debris that scoured and polished Yosemite’s granite rocks to a smooth surface, as seen on the rounded top of Half Dome and many other granite domes in the park today.
That still leaves the other half of the story. What the glaciers weren’t able to effect, erosion later did.
Once the last glaciers retreated, granite domes became exposed to the elements. Weathering causes sheets of exposed rock to slip away and fall due to cracks or joints in the rock, creating sheer faces like on the other side on Half Dome. This geologic process of weathering is called exfoliation, and it still continues through the park today. Sometimes weathering results in dramatic rockfalls in the Yosemite Valley.