Bridal Veil Falls + granodiorite at Yosemite June 1947

Bridal Veil Falls, Yosemite Valley.#25 p 4
June l947 photo by Commander John B. Barrett, USN Retired.The Bridal Veil granodiorite near the Falls contains fine evenly distrbuted light and dark materials with a salt-and=pepper appearance.Near Glacioer Point and Washburn Point on the south wall parallel biotite flakes and dark green hornblende rods dominate darker rocks now interpreted as granodiorite of Kuna Crest 91 million years estimated age.Half Dome granodiorite dominated the valley east of Royal Arches and Glacier Point.Aged about 87 million years, Half Dome granodiorite is the youngest plutonic rock around the Valley -medium to coarse grained with biotite plates and hornblende rods.It forms horizontal dikes at Church Bowl and in the cliff west of Royal Arches, and sheer cliffs north of the trail from Ahwahnee Hotel to Mirror Lake. These rocks are part of the Tuolumne Intrusive Suites, which extend to higher ground north and east of the Valley,with exposures on Tioga Road and TuolumneMeadows. The Cathedral Peak granodiorite is about 86 million years old,and the Johnson Granite Porphyry still younger. They appear to have originated in a single magma chamber whose composition changed over time because dark magnesium-rich hornblende and biotite crystallize and solidify at higher temperatures than quartz and feldspar.These dark minerals concentrate in the older rocks around the EDGE of the chamber,while the lighter minerals remain molten in the center.Nearly all the plutonic rock within the park was formed in the Cretaceous age 145-65 million years ago. The walls of Merced Gorge and the western end of the valley are relatively old.These include diorite of the rockslides below El Capitan,the granodiorite of Arch rock,and the tonalite of the Gateway along El Portal Entrance Road. About 108 million yearsago El Capitan granite intruded into these older rocks. It now dominates the western half of the valley and the monoliths of Turtleback Dome,Three Brothers,Cathedral Rocks, and El Capitan itself.El Capitan granite contains phenocrysts- large crystals embedded in finer material.These are absent from the Taft granite, whivh later intruded and forms the brow of El Capital and the upland toward Fireplace Bluffs.Taft granite is finer textured and lighter in color- it also occurs at Dewey Point and near the Fissures on the south wall of the Valley. Diorite dikes create dark patches on the face of El Capitan.
Subject:	Bridal Veil Falls(Y) Yosemite
Year:	1947