Fort Collins, Colorado — Robert Johnson isn't quite sure when it happened.

But some time on Dec. 14 — a sunny Friday a week and a half before Christmas — a mysterious benefactor dropped a solid gold surprise into his Salvation Army kettle.

The 1-ounce gold South African Krugerrand coin, valued at about $1,500, was spotted by collection counters later that day. With it, a 20-year Fort Collins tradition continued.

Almost every year since 1998, an anonymous donor has dropped at least one gold Krugerrand coin into a Fort Collins Salvation Army kettle in the weeks leading up to Christmas.

The only year the donation was not made was in 2001.

Some years have yielded two Krugerrand coins, which have sometimes been wrapped in notes, Christmas poems or a dollar bill. Occasionally, the Salvation Army also sees one or two gold U.S. Liberty coins anonymously donated each year.