Half Dome from Tunnel View, Yosemite National Park
Half Dome from Tunnel View, the classic view of the Yosemite Valley.
In common with the rest of the Yosemite peaks, Half Dome consists of a coarse-grained granite mass which forms part of the batholith of the Sierra Nevada mountain range. The rocks were formed deep underground in 'plutons' of molten magma during volcanic processes, then lifted to the surface by subsequent earth movements. The distinctively rounded profile of Half Dome - and the rounded adjacent peaks seen in this image - is a result of scouring and smoothing by glaciers during the Sherwin glacial period, around a million years ago. Weathering (notably freeze-thaw action) of the domed surface layers has caused them to break up into plates, creating one of the world's most notable exfoliation domes.
(This is a high-resolution scan from a 35mm original in my pre-digital archive).