are characterized by overhanging sidewalls that are relatively dry compared to the lower level rocks below the zone of seepage. The development of theater heads has been related to “ground-water flow direction, jointing and faulting, permeability contrasts, formation slope and dip angles, and formation cohesion”. The morphology of channels and valleys created by sapping are highly dependent on regional scale geology, and can be hard to distinguish from features created through alternative processes. Chemical precipitates can be used as indicators of groundwater water discharge implying that a valley or channel may have been formed as a result of sapping. These sorts of clues are important in areas where water is not currently being discharged. Notable landmarks Colorado Plateau Many “natural amphitheaters” can be found near the Colorado River. It is thought that sapping may have been more common in this area in the past when there was a higher water table. A shift in the climate and associated precipitation or the incision of the Colorado River are two factors that may have caused a change in the water table level. Mars Short, stream-like, deep channels have been observed on Mars. Very similar to valleys created by groundwater sapping here on Earth, the discovery of the Martian valleys has prompted numerous studies that aim to better understand the process of sapping. See also Headward erosion Groundwater discharge Valley networks (Mars) References External links Simulation of Groundwater Sapping Alan D. Howard, "Introduction: Groundwater Sapping on Mars and Earth" in Sapping Features of the Colorado Plateau, edited by A.D. Howard, R. C. Kochel, and H. R. Holt, NASA SP-491, p. 1-5 (1988) Julie E. Laity and Michael C. Malin, "Sapping processes and the development of theater-headed valley networks on the Colorado Plateau," Geological Society of America Bulletin: Vol. 96, No. 2 (1985), pp. 203–217 (Abstract). Geomorphology Hydrogeology Aquifers