MitcheIN, as a 30+ yr. veteran of beach storm hunting here in CA, I've dug untold countless things like that. All sorts of fossilized conglomerates of fused iron, steel, sand, pebbles, rock, etc.... I've saved a lot of it, just for conversation sakes, WHEN they contain coins. Ie.: a nail or spike or something that ....... like yours ..... leaches out through the decomposition process, fuses with the sand and minerals in cesspool like conditions in the bedrock. And sometimes coins, that happened to be in the proximety of the rotting iron/steel object, get fused in with the mass. So when you pull them up, you can sometimes see the rims of coins sticking out at you.
This is because for these formations to form, it has to be an un-moving still-object. Because if it were loose, and moving in and with the seasonal regular sand movement, it would be tumbled clean and erode to nothing eventually (since steel and iron rust fast in harsh salt water environment). But when the rusting object is stuck in the bedrock (or way far back in the dunes where storms haven't gotten back to in 50 or 100+ yrs.), they just decompose into these interesting growing shapes, incorporating in what's around them. And since bedrock like this, is often the depth to which coins since too (since they can't sink further than bedrock), thus you often find multiple nails, and some coins, all fused together, since they all tend to find themselves at this level, over time.
Then at some point, a storm erodes down to bedrock, and these things get released into the regular inter-tidal zone. Then you come along and find it within a few years
The reason I tell you all this, is that I'm convinced the process does
not take THAT long to happen. I have seen, for example, mere wheaties or buffalos (relatively recent drops) fused with such masses. And the iron itself, might be a RR spike for instance. (definate tell-tale RR spike, NOT a ship spike of some sort). And since the RR's didn't lace CA till the 1870s at the earliest, you can see that these things don't necessarily have to be that old (ie.: mission era, etc...)
Thus you may simply have a 1950s butter knife, for instance. JMHO.