In a lush, green corner of Golden Gate Park, Jeff Cross and his wife Sequoia are trying to find something that has been hidden for 36 years.
"Drove down from Eureka, to specifically dig right here," he says, stabbing a piece of rebar at the sandy soil.
Jeff and Sequoia are not the only ones who have come here, hoping to find something underground.
In recent months, people from far and wide are descending on San Francisco because of a book called "The Secret" published back in 1982.
In it, late author Byron Preiss laid out clues for 12 buried treasures hidden in 12 North American cities. More specifically, it's 12 casks; each one buried about four feet deep, each one containing a key that opens a safe deposit box containing one of 12 jewels.
As for those clues, they are spelled out in 12 verses, with each verse having a corresponding image that functions something like a coded map.
For 36 years now, jewel hunters and puzzle lovers have been pouring over the verses and images, trying to find these jewels and a lot of people are convinced that one of them sits somewhere in the city of San Francisco.
"So this, I'm guessing, if this is right, this is the western end of the park," says San Francisco Recreation and Parks General Manager Phil Ginsburg, analyzing the alleged San Francisco image.
Ginsburg didn't know too much about "The Secret" until searchers like Jeff and Sequoia became the subject of a recent cable TV show.
"Then, all of a sudden a bunch of other requests started coming in,"Ginsburg told KPIX-TV's Wilson Walker.
Now, people are digging all across the city, from the Marina Green to Mount Davidson, and spots all over Golden Gate Park.
"It's been really fun to kind of go back in time, and try and figure out what Golden Gate Park looked like 30 years ago," says Sequoia Cross. "What was here, what wasn't?"
It is, of course, entirely possible that the stash was somehow swept away in what is, after all, an ever-changing park. Was it ever in this park? Maybe so. Maybe not.
A lot of people have looked at this a lot of different ways. The volume and complexity of the theories are as mind-blowing as the puzzle itself.
There is, however, a word of caution for anyone that thinks they've got all of this figured out.
"If you're going to come to San Francisco and come to Golden Gate Park, or any other park in our city, and dig for treasure, yeah, ask first," pleads Ginsburg. "We'll help you dig, but we want our treasure hunters to dig with treasure rangers, folks who know about roots and irrigation lines."
As for Jeff and Sequoia's quixotic search, it was a lot of poking, a little digging, and no cask.
They, like every San Francisco jewel hunter before them, left empty handed this day.
Exactly where the verse and that mysterious woman are trying to lead them remains a very well kept secret.