From Yahoo News:
Here's how it all went down: Several years ago, Jason and Kelly were enjoying a picnic of Thai take-out on Ocean Beach when they noticed Amador creating a mural in the sand. "It was one of our first dates in San Francisco and it was just so cool," says Kelly. "We took a bunch of photos and it was a great memory."
Three years later, Jason tracked down the artist via the Internet and asked him to create a wedding proposal sand mural on February 12. The artist conceptualized the design and directed a handful of the couple's friends in raking it into Ocean Beach. It took them, according to Amador, about an hour and a half to get the job done; then everyone took cover on the sidewalk above the rocks.
Meanwhile, Jason was luring Kelly back to the picnic spot. "As we walked down the beach, we talked about the mural we'd seen years ago," Kelly says. "When we came upon the patterns in the sand, I couldn't believe the artist was back!"
Because the design was so large, Kelly couldn't read the message until she climbed up on the rocks (which took some coaxing). The waves were just starting to erase the edges of the mural when Jason pointed out the words and got on his knee.