For a route having two distinct exits on its own mainline, it's obnoxious that CalTrans opts to make CA 259 a hidden designation and sign it only as 'To CA 210' northbound, and more obnoxiously, as 'I-215' opposed to 'To I-215' from CA 210.
Shame it doesn't have a name for usasf.
I believe it's the northernmost portion of the San Bernardino Freeway.
I don't think so. The San Bernadino Freeway runs west-east, in the San Bernadino area along part of I-10 which is well south of CA 259. As far as I can tell, 259 has no name (which fits into my "glorified ramps" theory above).
I think even if it had a name, we'd be really straining here to include in usasf a route that is a numbered state highway, which would be in usaca if it had route number markers.
If we were going to stretch anything here, it should be our unsigned routes rule, based on that the route had route number markers about a decade ago, and the route number is shown on callbox signs (assuming that any callboxes remain on that route, since nowadays almost everybody has a cellphone). But CA 259 is just a crummy one mile long, hardly worth the trouble.