Investigation of the nature of the folding of the Cambrian Tonto Group strata in Grand Canyon necessitates first investigating the petrology of those strata. The Cambrian Muav Formation is a 42–252 m (136–827 ft) thick cliff-forming unit that outcrops towards the top of the Tonto Group along ~500 km of the walls of Grand Canyon and beyond. Erosion of the underlying Precambrian basement rocks produced the Great Unconformity on which the Tonto Group was deposited as part of the fining upwards Sauk megasequence that blankets North America and other continents. The Muav Formation consists of dominant thick and thin beds and laminae of limestones, sometimes with alternating siltstone partings, with minor dolostone beds and laminae and some extensive intraformational flat-pebble conglomerate layers. A few trilobites, brachiopods, and other invertebrates, as well as small shell fragments are found fossilized in the Muav Formation, along with traces and burrows left by worms and other invertebrates. U-Pb dated detrital zircon grains from the underlying Tapeats Sandstone coupled with biostratigraphic trilobite faunal zones correlated globally have constrained the conventional age of the Muav Formation to 499–502 Ma. Detrital zircon U-Pb ages from the underlying Bright Angel Formation identify the primary source of the silicate grains within the Muav limestones as the locally underlying Precambrian crystalline basement. Uniformitarian interpreted depositional environments for the Muav Formation are shallow marine to subtidal, intertidal, and tidal flats environments, yet it has been described as "one of the most dramatic global marine transgressions in Earth history." Calcite is dominant with subordinate dolomite, while quartz and K-feldspar contents range from 2.7% to 55.9% and 0.9% to 26.3%, respectively. Illite is present, indicative of the detrital muscovite flakes that are wedged between the other grains. The limestones are fine-grained and generally poorly sorted, with angular to sub-rounded, medium silt to fine sand-sized quartz and K-feldspar grains scattered through the tiny-grained calcite matrix (micrite), all cemented by recrystallized calcite. The dominant thickening, thinning, and pinching out of laminae, occasional current ripples, megaripples and cross-laminations, and some extensive intraformational flat-pebble conglomerate layers are consistent with rapid transport and deposition by high-energy storm-like surges, with spontaneous stratification of the heterogranular sediment mixture and of lime mud floccules. There is no evidence, macroscopic or microscopic, of any metamorphic changes to the detrital mineral grains or textures. Instead, the mineralogical content, textural features, sedimentary structures, continental-scale deposition, and even the tracks and traces of transitory invertebrates, all indicate rapid burial. Furthermore, all are consistent with the catastrophic erosion of the Great Unconformity near the initiation of the global Genesis Flood cataclysm only about 4,350 years ago, and the subsequent hurricane- and tsunami-driven rapid short-distance transport and deposition of the sediments that form the Muav Formation, likely in the first few days or weeks of that year-long event.