An explanation is offered, within the young-earth Flood model, for the origin of radioactive shales and clays via the alteration of volcaniclastic material (ash deposits) which contain radioactive elements. This is based on the similarity of radioactive elements identified as leaching from altered volcanic ash deposits in the western United States. The Southeastern United States has many marine organic rich "black" shales, massive clays, and sandstone layers which contain radioactive elements at levels significantly higher than the surrounding strata. The radioactivity associated with those clastics is derived from several radioactive isotopes including uranium (234U), thorium (232Th), potassium (40K), and radium (226Ra). Two specific stratigraphic units, the Chattanooga Shale of Tennessee and various clay units within the massive clastic deposits of the Hawthorn Group of west central Florida, are proposed as examples where radioactive volcaniclastics have altered in-situ to yield radioactive shales, clays.