I'm going to completely disagree with GLC's recommendation about going US-395 to I-15 to I-215 out to the I-10, for one major reason, Construction. In my previous post, I mentioned that there is construction on the Cajon Pass grade going in both directions. They have been closing 2-3 lanes (of 6) which causes major congestion. You *could* stay on CA-58 and take that to Barstow, take I-15 south to I-40, then at exit 144 in Needles, head south on US-95 to Blythe where you pick up I-10 east. Then use AZ-85 as described by both me and GLC, from I-10 to I-8 and pick up I-10 again at Casa Grande.
Believe me, I will do almost anything to avoid the Cajon Pass area right now. Maybe they've finished it, but as of 3 weeks ago, friends who headed to Vegas said they got stuck in that area in major traffic, at 10 at night! Construction!