The purpose of this study is to investigate the effects of weathering and erosion on the magnetic susceptibility of fresh plutonic rocks exposed on Cowles Mountain in San Diego, California. Fresh granite outcrops from 17 widely distributed locations within an ~5 km2 area yield consistent in situ magnetic susceptibility values with an average reading of 3027 x 1 o-5. Ten outcrops of weathered granite, which typically have weathering rinds
