The Cambrian Tapeats Sandstone rests unconformably on the Proterozoic Vishnu Schist. This unconformity represents a billion-years of missing geologic time, hence it's referred to as The Great Unconformity.
The irregular yellow line represents the surface of the The Great Unconformity separating the younger Tapeats Sandstone (top) from the ancient Vishnu Schist.
