San Francisco Mint Question

I don't remember where I read this, or even the particulars, but when I was a teenager I recall an article concerning one of the San Francisco mints. I'm 73 now, so it was quite a while ago. The article detailed how a sort of time capsule was placed in the cornerstone of the building and there were coins placed as part of the contents. One of the coins was a gold piece (2 1/2 dollar maybe) and it was a very rare date. Anyone know about this? Am I hallucinating, or perhaps wildly inaccurate? If I have some of the facts right is the status of the time capsule known? I grew up in what is now known as Silicon Valley and I remember thinking, "Hmmmm.....a quick trip to the City with a friend or two and sledge hammer and........