We found 1 Reddit comments about The Jepson Manual: Higher Plants of California. Here are the top ones, ranked by their Reddit score.
I assume you already have a copy of the Jepson Manual and / or are familiar with eFlora. Sort of the de facto gold standard for California. You can get a used older edition pretty cheap and other than moving a few species around it's still a very usable, if not very portable book.
I'd point out that California has one of the richest floras in the world. In some ways though, it's characterized by a large number of species and subspecies within many of the genera. So if you can learn to recognize for example a plant from the genus eriogonum or arctostaphylos at a glace, keying it out to the specific species will be much more simple. Learn to spot the major genera of the area because the exact species you will encounter might be different than you would see just a few miles away and you will never remember them all, the book is 1600 pages.