The Granite Gorge Metamorphic Suite consists of lithologic units, the Brahma, Rama, and Vishnu schists, that have been mapped within the Upper, Middle, and Lower Granite Gorges of the Grand Canyon. The Vishnu Schist consists of quartz-mica schist, pelitic schist, and meta-arenites. They exhibit relict sedimentary structures and textures that demonstrate that they are metamorphosed submarine sedimentary rocks. The Brahma Schist consists of amphibolite, hornblende-biotite-plagioclase schist, biotite-plagioclase schist, orthoamphibole-bearing schist and gneiss, and metamorphosed sulfide deposits. As inferred from relict structures and textures, the Brahma Schist is composed of mafic to felsic-composition metavolcanic rocks. The Rama Schist consists of massive, fine-grained quartzofeldspathic schist and gneiss that likely are probable felsic metavolcanic rocks. On the basis of the presence of relict pillow structures, interlayering of metavolcanic strata, and the large volumes of metavolcanic rocks, the Brahma and Rama schists are interpreted to consist of metamorphosed, volcanic island-arc and associated submarine volcanic rocks. These metavolcanic rocks are locally overlain by the metamorphosed submarine sedimentary rocks of the Vishnu Schist that are interpreted to have accumulated in oceanic trenches. These metasedimentary rocks were originally composed of particles of quartz, clay, and volcanic rock fragments that have become metamorphosed into various schists. The Vishnu Schist exhibits relict graded bedding and structures indicative of turbidite deposits that accumulated in oceanic trenches and other relatively deep-marine settings. The Brahma Schist has been dated to about 1.75 billion years ago. The felsic metavolcanic rocks that comprise the Rama Schist have yielded an age of 1.742 billion years ago.