Solo said:
It's going to ba a hot one. Plan for HIGH temps anywhere south of and including Las Vegas.
What he said. No, really!
Seriously, from about Cedar City UT to Victorville CA you'll be broiling in 110-degree+ temps. Then you're dealing with LA traffic, which is no picnic until you get to Santa Barbara.
You are of course welcome to head my way, and I'm definitely down to meet up with you. But if it was my trip, I'd say cut off the southern part and head west instead from SLC through Tahoe and into Cali. Then southwest to San Simeon or Carmel and back north on Hwy 1 to Portland and points east. Better weather, plenty of awesome sights along the way, plus you won't have to deal with quite as much of that "I'm sitting underneath a giant hairdryer for 700 miles" feeling.