Soaproot

"Finding a round stone she could hold easily in her hand, Iza pounded the soaproot with water in a saucerlike depression of a large flattish rock near the stream. The root sudsed into a rich, saponin-filled lather. ...after a thorough wetting, the woman picked her up, sat her on the rock, and lathered her from head to foot, including her stringy, matted hair." CCB