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.
Considering that this is a major connector between two freeways with its own exits (E St northbound, unshared with CA 210; Base Line southbound, shared with I-215; and Highland Ave both directions), and we do have unsigned Interstates in the database, most notably I-305, which CalTrans doesn't even acknowledge, I'd argue that CA 259 fits the bill for a variance and should be included, the fact that all the online maps (Gmaps, MapQuest, OSM, Bing, RMN [Yahoo seems to be dead?]) all show 259 notwithstanding.