Vishnu Basement Rocks
They form the crystalline basement rocks that underlie the Bass Limestone of the Unkar Group of the Grand Canyon Supergroup and the Tapeats Sandstone of the Tonto Group . 
<triplet> Bass Limestone <subj> Unkar Group <obj> part of <triplet> Unkar Group <subj> Grand Canyon Supergroup <obj> part of <triplet> Grand Canyon Supergroup <subj> Unkar Group <obj> has part <triplet> Tapeats Sandstone <subj> Tonto Group <obj> part of <triplet> Tonto Group <subj> Tapeats Sandstone <obj> has part