August Laufenburger was buried in the Knights Valley Cemetery in Sonoma County, according to his death certificate (and we all know death certificates are perfect, right?). The dates on the certificate match the tombstone dates and the additional information all points towards this portion of Sonoma County. (Most people did business in Calistoga in Napa County because it was the closest town.)
I've been in touch with the cemetery and although they aren't familiar with that name, it might be because the tombstone has been missing for so many years. They will research the name (and have similar names like "Laufenberg") so August may be a fit after all. If it is indeed a match I'll drive up to Shasta and bring the stone back here for placement on the grave.