Great site to keep track of where colors are changing: https://www.californiafallcolor.com/map/
And I really recommend this book: https://www.amazon.com/Californias-Fall-Color-Photographers-Autumn/dp/1597143170
I picked it up in June Lake a couple years back when camping in early October to enjoy some fall color. More of the Sierras, but the color up there at this time of year is amazing. I personally love the June Lake loop.