U of Nevada Reno would be an affordable safety (WUE + merit), only 15 miles from the CA border, close to Tahoe skiing, and very solid STEM.
U of Utah is another - a bit farther but still pretty easy to get to. Strong STEM, strong music, incredibly close to great skiing, and very affordable (generous merit, and either WUE or the path to residency after the first year).
Worth weighing these flagships in nearby states vs. the CSU safeties he’s considering. Your list seems good, but in California, some schools in neighboring states can be closer to home than schools at the far end of California, so look more at actual ease of access and potential cost than just at whether it’s in CA. Sometimes the non-CA schools can offer more flexibility for a kid who’s not 100% set on his major.