Routine measurements of the magnetic properties of various geological formations show that 'granite' wash, although having an appearance in well samples very similar to that of unweathered 'granite,' has very different magnetic properties. Magnetic logs of wells located in Southwestern Oklahoma, Texas Panhandle and Eastern New Mexico show a large increase in the magnetic susceptibility when unweathered 'granite' is encountered. Samples of 'granite' and 'granite' wash collected from the Wichita Mountains in Oklahoma show a marked decrease in magnetic susceptibility during the formation of 'granite' wash from unweathered 'granite.' It is concluded that magnetic logs made by testing well samples will be of assistance in differentiating 'granite' wash from the underlying unweathered 'granite.' Tests of samples of unweathered 'granite' upon exposure to weather show a measurable to marked decay of susceptibility and remanent magnetism in the relatively short time of a few years.