The volcanic rocks inside the park include basalt and andesite flows and dacite flows and tuffs. The Mono Craters east and southeast of the park are rhyolite volcanoes that erupted stubby flows and tuffs from about 30,000 to 650 years ago. Example of older metamorphic and younger volcanic rocks in Yosemite.

There is no active volcano within Yosemite National Park; instead, the park is famous for its massive granite monoliths, which are the "roots" of ancient volcanoes that erupted over 100 million years ago. The cliffs like El Capitan and Half Dome are made of plutonic igneous rock (granite) that formed when molten magma cooled slowly deep underground, never reaching the surface to erupt. These "plutons" were eventually pushed upward and the surface volcanoes eroded away, leaving the hard granite behind. However, Yosemite is located very close to the Long Valley Caldera and the Mono-Inyo Craters, which are part of an active volcanic system just east of the park. In 2026, visitors can see small amounts of "extrusive" volcanic rock within the park, such as the columnar basalt at Little Devils Postpile. While the park itself is a landscape of glacial erosion and ancient magma chambers, it is not a "volcano" in the way Yellowstone or Mount Rainier are, but rather a spectacular display of what lies beneath a volcanic chain once the fire has died out.