In geology, a facies is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks and the changes that may occur in those attributes over a geographic area. A facies encompasses all the characteristics of a rock including its chemical, physical, and biological features that distinguish it from adjacent rock.

Geology is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth sciences, including hydrology. It is integrated with Earth system science and planetary science.