Figure 1. Representative mountain-front exposures of Middle to Upper Cambrian carbonates paired with Sr and C isotope stratigraphic variations through the study interval. Lower photo of Middle Cambrian Mount Whyte, Cathedral, Stephens, and Eldon formations exposed at Castle Mountain, southern Canadian Rockies. Upper photo of Middle to Upper Cambrian Bonanza King, Dunderberg, and Nopah formations exposed at Pyramid Peak, southern Great Basin, United States.