The Permian Phosphoria Formation of the western United States represents some 15 million years of sedimentation, reaches a thickness of 420 metres (1,380 ft) and covers an area of 350,000 square kilometres (140,000 sq mi).[1] The formation is a phosphorite and an important resource of phosphorus.
The formation reaches its greatest thickness in the Sublett Range in the Paleozoic cordilleran structural basin of southern Idaho. Within the basin the formation consists of a basal phosphorite overlain by a thick sequence of chert and cherty sandstone. To the east in western Wyoming the Phosphoria gradually decreases in thickness and is intertongued with carbonate rocks of the Park City Formation and redbed sandstones of the Chugwater Formation of Permian to Triassic age.[1] The Phosphoria units extend into the Wind River Mountains and pinch out in the Green Mountains to the east. The formation consists of a lower Meade Peak and an upper Retort phosphatic shale members. It is underlain by the Pennsylvanian-Permian Casper Formation and overlain by the Triassic Dinwoody Formation.[1]