Subsequent erosion of the Targhee Uplift was driven by steepened stream gradients. Gravel, quartzite cobbles, and sand from this erosion eventually became the 5,000 foot (1,500 m) thick Harebell Formation seen today as various conglomerates and sandstones in the northern and northeastern parts of the park. In the Paleocene epoch large amounts of clastic sediment derived from uplifted areas covered the Harebell Formation to become the Pinyon Conglomerate. The lower members of this formation consist of coal beds and claystone with conglomerate made of quartzite from the Targhee uplift above.