Slag, I live in the Crescenta Valley, nestled between the foothills that are laughingly called the Verdugo Mountains and the western end of the San Gabriels. We're northwest of Los Angeles; Upland is about 25 miles east of us.
Highway 58 still connects the Barstow with Bakersfield. I believe that this is the route the Joads took into Bakersfield area. It's been over 40 years since I read Grapes of Wrath, so I may be wrong on that.