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 Bright Angel Formation is a 82-137 m (325-450 ft) thick slope-forming unit that recessively outcrops in the middle 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 Bright Angel Formation consists of ~40% green, strongly laminated shales, ~30% crumbly and well-laminated siltstones, and ~30% sandstone beds. The latter are often hard and ledge-forming, some are conglomeratic, and most are variously cross-laminated, indicative of high-energy water transport. Trilobites, brachiopods, and other invertebrates, as well as shell fragment "hash" are found fossilized in the Bright Angel Formation, along with abundant tracks and traces left by trilobites and other invertebrates, and cryptospores of land plants and algae, but not marine algae. 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 Bright Angel Formation to 502-507 Ma. Detrital zircon U-Pb ages from the formation identify the primary source of the sediments as the locally underlying Precambrian crystalline basement. The uniformitarian interpreted depositional environments for the Bright Angel Formation are intertidal to subtidal shallow-marine environments, yet it has been described as "one of the most dramatic global marine transgressions in Earth history." While quartz is dominant, K-feldspar content ranges from 11.0% to 46.9%, various carbonates are present up to 32.4% and illite is ubiquitous, indicative of glauconite and of the detrital muscovite flakes that are wedged between the other grains. The shales consist of alternating thin illite-dominated laminae interstratified with thin laminae of siltstone. Grains are angular to sub-rounded, and the fabric is cemented by silica as quartz overgrowths. The strongly cross-laminated sandstone beds and the laminated siltstones and shales are consistent with rapid deposition by high-energy storm-like surges, with spontaneous stratification of the heterogranular sediment mixture and of 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 4350 years ago, and the subsequent hurricane- and tsunami-driven rapid short-distance transport and deposition of the Bright Angel Formation, likely in the first few days or weeks of that year-long event.