Remolded clay seams abundant in the sedimentary stratigraphic sequence in western San Diego County, California, are defined as bedding-plane faults. These bedding-plane faults predate existing landslide slip planes though normally coincident with them. The physical characteristics of the bedding-plane faults are remarkably uniform, regardless of the geological unit or geographical setting in which they occur. Measured values of the ultimate friction angle range from 6 to 12 degrees; effective ultimate cohesion is usually less than 200 pounds per square foot (psf); water content is near or slightly above the plastic limit; the liquid limit ranges between approximately 77 and 85; and the plastic index ranges from 40 to 60.
The bedding-plane faults originated through stress relief along weaker beds during tectonic deformation. The pre-existing plane of weakness can be used for analytical purposes in the evaluation of slope stability.