I would wonder why not Olympic though- also being in San Fran area...
Looking through the threads, it appears when this game very first started, it was only a CTTH Bali Hali, Thereafter, Kiawah was the first 9 holes. We know from MisterWGT's comment in 2010, about gators on Kiawah, it was probably around that time frame. Next came St. A front 9 and the back was a CTTH and then Beth Page was added as it was the sight of the 2009 US Open.
Yancy's comments about the 5th year anniversary, and when he started looking for Bigfoot suggest that he knew about Bigfoot pretty soon after Beth Page was added. This would put the addition of Beth Page in 2010.
Olympic was not added until May, 2012, the same year it hosted the US Open. I am sure that if Olympic was added before Beth Page, Bigfoot would have been on Olympic, provided a great place to hide.
Note, the US Open has a lot of meaning on WGT. All the signs found, so far, on Chambers Bay, all have the name of a course which hosted the US Open.
EDIT: After reading MIO and Dodgy's replies, and they would know, better than me, I was incorrect as to 2010 for Beth Page, it was 2009. I did not make the change above as their replies reference, and respond to, my post above as originally written.