OAKLAND, Calif.—The Oakland Museum of California is offering a $12,000 reward for the safe recovery of a rare Gold Rush-era quartz and gold box that was stolen.

Museum officials said on Wednesday that the box was a wedding anniversary gift from a San Francisco man to his wife in the 1800s. It was taken during a break-in on Monday.

It had been in the museum's collection since 1960.

Oakland Mayor Jean Quan's chief of staff, Anne Campbell Washington, told the San Francisco Chronicle (http://bit.ly/WLZwJ0) the box was valued at more than $800,000.

Monday's break-in was the second at the museum in as many months. Pieces of gold and other valuable historic artifacts were taken in November.

Another Northern California museum and a county courthouse have also been hit by gold thieves over the past year.