I'm new here, but have been following this case for a long time.
I hope Anna's family get the answers they've been waiting for. (For what it's worth, based on these threads and everything taken together, I don't believe this is Anna).
-----------
Regardless, San Gregorio State Beach . . .
If this is a state beach, it may be part of the Department of Parks and Recreation or some other such entity. Almost always these types of beaches are cleared at the end of the day. Lifeguards or workers walk along the shore and collect items that have washed up or been left behind--buckets, boots, clothing and the like. (This is true where I live, and the park rangers are often lifers). What do they do with these items that are unclaimed? Maybe they log the items? Donate them?
It occurs to me that in the weeks or months prior to this bone washing up that other items could have come ashore as well and been placed in the bucket, held for a few weeks, donated or logged? If a worker were to find a rain boot (or something else exclusive to Anna) he or she would not have phoned the police as these things are common finds on beaches. Given that a bone fragment was found, the workers may remember other items that washed up during this time frame more vividly than at other times.
This is a long shot, but does anyone think these types of things would have been logged or remembered, especially in the days or weeks following the discovery of the bone?