The Vishnu Basement rocks as aforementioned includes all Proterozoic crystalline rocks in the canyon. The oldest section of the basement rocks is the Elves Chasm pluton. These rocks were exposed to erosion and then buried by the Granite Gorge Metamorphic Suite with both volcanic and submarine sediment. Younger rocks of the group include various plutons like the Zoroaster, Ruby, and Diamond Creek plutons. These are intrusive rocks that are traces of volcanic arc systems that cut through older groups.A second intrusive group was formed from granite/pegmatite magma that filled cracks in the Granite Gorge Metamorphic Suite. The Cottonwood, Cremation, Sapphire, and Garnet complexes all cut through the Suite. Some ultramafic rocks exist in the Inner Gorge, around Salt Creek, Granite Park, and Diamond Creek. These are unnamed but likely came from fractional crystallization of plutons. Contact is with either the Tonto Group or the Unkar Group. This is known as the Great Unconformity (termed by JW Powell). This marks an unconformity between the Tonto Group, the Grand canyon Supergroup, and the Vishnu Basement Rocks. Between the Tonto and Vishnu layers is considered a nonconformity. During Precambrian times, the core of the North American continent was comprised of a craton, or stable section of the lithosphere, called Laurentia. Part of the Great Unconformity was caused by the submergence of Laurentia in a shallow cratonic sea which then deposited marine sediments in the region. This region is unusual in its scope, extending from Lake Superior, to Glacier National Park, to the Grand Canyon.