Didn't it appreciate very rapidly in the 1930s? Once?
Yes, it appreciated very rapidly in the thirties since the federal government reneged on the gold clause. That is, contract law. The government's position was that the citizenry was "hoarding" gold. So they confiscated all they could. Somehow, keeping all that gold at Ft. Knox isn't "hoarding".
Enhhhh.... I guess that could be argued but in reality the government re-valued Gold and it stayed at that same value for nearly 40 years. Since the re-valuing took place post confiscation of Gold from US citizens, individual investors were generally unable to profit. It has only been since 1971 that Gold has fluctuated in price like other investments and individual investors have been able to profit during times of appreciation.