I left SB from Sumas WA August 29 and would have gotten snowed on in Big Bear on October 2 if I hadn't bailed a few days earlier at Cajon Junction. Temperatures southbound were under 95F even in the Mojave desert. Also, almost no rain.

Some of the alternate routes are gravel.

Other than long climbs, followed by brief, but screaming descents - sometimes 2 or 3 times a day, you'll have to contend with the traffic on often-shoulderless Hwy 89 from Mount Shasta to Truckee. Very dangerous.

+1 on the ACA maps.

As far as scenery goes, the Icefields and the GDMBR were much better.