Nahachish Rock is located on the northerly margin of Rainbow Valley in northern San Diego County, California (Fig. 1). This feature is supposed to represent the solidified remains of an important person in Luiseno mythology. This paper describes the location of the Nahachish Rock, compares its appearance in the mid-1920s and the mid-1980s, comments on some aspects of the mythology associated with the person Nahachish and, wherever possible, provides definitive locations for the several places visited during his travels.