A pronounced oxidized zone is characteristic of the sedimentary members of the Tertiary Artist Drive and Furnace Creek Formations on the east-central flank of Death Valley, California. Light-colored rocks of the deformed formations represent an oxidized zone in initially dark-colored rocks that originated in the reducing environment of a perennial lake. Oxidation of iron accounts for the color change. The interface between oxidized and unoxidized rocks is generally 50 to 150 ft (15 to 46 m) below the ground surface and is sharply defined as a planar, subdued replica of the surface topography. The well-developed interface may be the result of simple downward-progressing weathering; however, evidence suggests that it may be the vestige of a “paleo-water table” except where locally modified by oxidizing meteoric waters, erosion, and tectonic activity.