Geological study of the Chaos Crags began in the late 1920s, when Howel Williams wrote about its pyroclastic rock deposits, rockfall avalanches, and the dome-producing eruptions. Though Williams initially suggested that volcanic activity and the ensuing landslides took place about 200 years ago, additional study of the rockfalls by James P. Heath placed their age between 1,500 and 300 years ago. This was followed by mapping of the Manzanita Lake and Prospect Peak quadrangles in the 1960s by Gordon A. Macdonald.