That's Highway 243 in CA, about halfway (as the crow flies) between Hemet & Palm Springs. Just a little ways South of Banning along I-10. Headed North, INTO banning, if I'm correct...
Somewhere in the near vicinity of Mt. San Jacinto.
My Grandfather lived in Beaumont, CA when I was a kid, so I remember going on family vacations/day trips with him out there.