A planar surface at the base of the landslide along which motion has occurred; it separates the material that has moved from the stationary material.

A fracture or break in underground rock usually resulting from tectonic stresses along which one or both sides move. Movement along faults may produce earthquakes; most faults are relatively minor with movement involving only a few feet.

A body of rock identified by physical characteristics and stratigraphic position and mappable at the earth's surface or traceable in the subsurface. The formation is the fundamental unit in lithostratigraphic classification. Formations can be subdivided into members or lumped together into groups.

Water containing only small quantities (generally less than 1,000 milligrams per liter) of dissolved materials.