Well, Jim, I own property that extends into the middle of a public road. It's on the plat. I could legally build a fence thru the middle of the road. I don't because I get along great with the road crews and they've done a few favors for me with their heavy equipment.
I haven't decided what to do yet. Maybe I'll trade this piece for property the county owns.
You may be one of the 1% to 5% that have a legitimate claim. I repeat the word "may" until someone else (an independent third party) does a title search and checks the chain of ownership. I can tell you from personal experience, though, that most people who make a claim that they own public property, don't.
Don't do it!
What you own is the "underlying fee," not the surface rights. In California, as in most of the states, you do own the fee to the centerline of the road, but it is encumbered by an easement that is held either by the city/county, or if it is a private road, by adjoining property owners.
If you make the mistake of blocking the road, you will get stuck for the cost of un-blocking it, plus the court costs to adjudicate the matter. Bad idea!