This website is by no means the end-all, be-all of getting out into nature on transit. Some other resources that I’ve found continually helpful for myself have been:
LA Transit to Trails: a curated guide to transit-accessible hikes around the greater Los Angeles area
Pacific Crest Trail Association: Getting to the Trail: the official PCTA guide to getting to and around the trail, including rural Californian transit agencies and shuttle services
Marin Transit: Transit to Parks: Marin Transit’s official page detailing the Marin-area parks their services run to
County Connection: Places to Go: County Connection’s list of destinations including local museums
Golden Gate National Parks Conservancy: How to take public transportation to GGNRA parks: A guide to exploring different parts of the Golden Gate National Recreation Area by transit, plus what to keep an eye out for
California Protected Areas Database: a map from Greeninfo Network showing all of the protected land in the state
Climate Action Center - Bikes on Transit Information: Want to take your (e)bike on transit to help you go farther and see more? This site has detailed bike-friendliness information on each of the operators in the Bay Area