For comparison with the previous juvenile Semipalmated Sandpiper, here is a juvenile Western Sandpiper. It is slightly larger with a more tapered bill. It has a more contrasting pattern on the mantle, but less contrast on the crown. This individual seems to have a slightly deformed bill.
Western Sandpipers are abundant migrants and winter visitors to California, but they also migrate through much of Eastern North America and often winter regularly on the southeast coast and gulf region.
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope 3 | 30X WA | hand-held (no adapter)