Composite Dike

Beautiful, glacially sculpted slabs of rock in the Yosemite high country display interesting petrologic relations. Diorite (dark-gray rock) intrudes slightly older aplite dikes (white rock) in this photo. The surrounding light-gray rock (oldest) 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.