Not that familiar with claims in CA, but it appears that detecting is allowed. Just remember to back fill any recovery holes.
As to the area being claimed up, that is pretty common in any area where gold is found. Signs have a way of disappearing, sometimes overnight. I tend to plot out the boundaries on a map to be sure of staying on the claim.
If interested in other spots and if they are claimed, looks to LR2000 (will get it down to 1/4 section), then check with BLM state office to dig deeper, and finally with the county recorder for the final say on if any claims are current.