"Has anyone here successfully gathered wild onions in California?"
Yes. Look for them in the marshy margins along lake outlet streams up to ~10,500'. The leaves look a lot like daffodil leaves(both are members of the lily family) and, when rubbed, emit that telltale onion smell. You will have to dig them out with a sharp stick, potty trowel, etc. If they are flowering, it is even easier to identify them. The leaves can be a little fibrous, but are still very tasty, and the white part is a little tough but still edible and very tasty in soups, mashed potatoes, etc, or stuffed in the belly of a trout before baking in foil.