Volcanoes

• The Sierra Nevada Mountains rose from granitic rock that formed from volcanic eruptions during the Mesozoic Era, the time period that spanned 250 to 65 million years ago. Magma rose up through older, Paleozoic rock and cooled below the surface to form a massive, single piece of embedded granitic rock.
  
  

Erosion

• Approximately 80 million years ago, during the late Cretaceous period, the layer of sedimentary rock that covered the granitic rock began to erode. Millions of years of erosion wore away the surface rock to expose the younger, granitic rock beneath.
  
  

Crust Movement

• Crust movement formed the basin east of the mountain range approximately 20 million years ago. Less than 5 million years ago, the basin area dropped and the range area to the west of the basin began to rise. The east side of the range rose steeply from the basin while the west side rose gradually.
  
  

Ice Age

• Glaciers formed in the highlands of the Sierra Nevada Mountains during the Pleistocene Epoch, around 2 million years ago. As the glaciers moved downstream they carved U-shaped valleys. The steep cliffs of Yosemite National Park are evidence of past glacial movement through the Sierra Nevada Mountains.