How was Wyoming coal formed?
During the late Cretaceous to early Tertiary period in Wyoming, thousands of feet of rock debris were eroding from the mountains. All this rock was deposited in basins (or valleys) between the mountains. The climate was humid and mild (which is a marked contrast with the present climate). The basin floors were covered with dense, rich forests and were often filled with water. Then, the region was uplifted again and debris was deposited in the lower basins.
