An Introductory Guide to Trail Planning and Decision Making," is published by BLM and the Oregon Trails Coalition. Even though it it wasn't made for California, the planning steps are the same.
Turn a great idea for a new trail and make your vision a reality. You’ve heard that the process requires
patience and persistence, this guide explains the necessary steps. This trails planning guide was a collaboration between land managers, trail planners, and trail user groups.
The online version is free. You can download (BIG file) or read
it at Trail Planning Made Clear HERE.