Old Faithful, the jewel of --------------------------- in Calistoga, California, is not as dependable as it used to be. Because of vandalism and age-old geological shifts, the world's largest geyser is slowly losing its reputation for erupting like clockwork. In 1970, the average time between eruptions of the 126-year-old geyser was 66 minutes. The average today is about once every 77 minutes, or 18 times a day instead of 21. The geyser's power hasn't diminished, however.?