Stockton as an Oakland Destination

Aside from showing the older-style button reflectors still common on California signs, this destination sign at a freeway entrance from Grand Avenue in Oakland shows something a bit odd. The destination for this sign usually would be San Leandro or Hayward, both not so far away along Interstate 580. But Stockton? To reach Stockton from this point requires following Interstate 580 until reaching Interstate 205 in San Joaquin County. That's almost an hour and a half from this point on a good day. San Francisco is much closer.