Johnson Granite Porphyry is found in Tuolumne Meadows, Yosemite National Park.
Johnson Granite Porphyry was named for Johnson Peak, the highest mountain in Tuolumne Meadows, Yosemite National Park.
Its area is estimated at , the exposed area covering roughly .Glazner, Allen F, Stock, Greg M. (2010). Geology Underfoot in Yosemite. Mountain Press, p. 53. . Johnson Granite Porphyry is part of the Tuolumne Batholith. Its boundaries are difficult to trace, and are irregular. It is both the youngest, and the most siliceous rock of Tuolumne Intrusive Suite.
Geology
The innermost, most felsic part of the Tuolumne Batholith is the Johnson Granite Porphyry. It is a highly irregular, elongated body. Completely surrounding it is the much larger body of Cathedral Peak granite.
Field observations and magnetic fabrics suggest an extrusive event, that is, Johnson Granite Porphyry may record possible volcanism. This may relate to deformation along active shear zones.
Johnson Granite Porphyry is composed of
quartz K-feldspar zoned plagioclase, and locally contains coarse-grained feldspars Biotite, the only mafic mineral, with accessory phases of; sphene, allanite, apatite, magnetite.
See also
Cathedral Peak Granodiorite El Capitan Granite Fine Gold Intrusive Suite Geology of the Yosemite area Intrusive Suite of Buena Vista Crest Intrusive Suite of Merced Peak Intrusive Suite of Sonora Pass Kuna Crest Granodiorite Porphyry Sentinel granodiorite Tuolumne Intrusive Suite
References
External links and references
Reference with a photo Geologic and geophysical investigation of two fine-grained granites, Sierra Nevada Batholith, California: Evidence for structural controls on emplacement and volcanism National Geologic Map Database site