Garden Rock “Turtle Island” is a quartzite which originates from the Late Proterozoic (750 to 700 million years ago) Pocatello Formation. The quartzite was originally a sandstone which was deposited during a time of continental rifting within fault bounded basins. The Pocatello Formation was buried beneath a sequence of Paleozoic (542 to 251 million years ago) sedimentary rocks. The Pocatello Formation was folded and faulted by compression produced during the Cretaceous Period (144 to 66 million years ago). The formation was later exposed by erosion and faulting produced by east west extension during the (24 million years ago to present). The Pocatello Formation has been metamorphosed due to the depth of burial beneath overlying stratigraphy, pressure produced by overlying stratigraphy, and past tectonic events. Turtle Island was sourced from the Portneuf Gap area..

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