Exfoliation

Exfoliation or 'sheet jointing' is well exposed on the eastern dome (lowest of 3) of Mt. Starr King in Yosemite. These joints form parallel to topography, in response to the release of pressure due to the removal of overlying material (i.e. erosion). This process helps to form the domes of the Sierra. The rock in this photo is Half Dome Granodiorite (~88-90 Ma). Ma = million years old; a crystallization age. You can click here to see a description of specific rock types.