The Phosphoria Formation of the western United States is a geological formation of Early Permian age. It 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). The Phosphoria includes phosphorite beds that are an important source of phosphorus. Many of its shales are rich in organic matter and are petroleum source rocks, and some of its dolomites include petroleum reservoirs.