I spoke with "Jordan" (831-345-1397) who IS authoritative at State Parks and he said that a combination of California Code of Regulations Title 14, Section 4326(a), together with "District Superintendent Posted Orders" (at the entrance kiosk off Hwy 9) makes all areas  of "Lower Highway 9 South of Garden of Eden, except on designated roads" to be off-limits (to BOTH cyclists and even pedestrians / hikers).

The "designated roads" I have (and the website has) clarified above.  So, now I am certain:  access=no is the correct tag according to State Parks, state law and OSM's tagging principles for access (=no).

I'll assume the same for UCSC, but if you want me to call my former colleagues at TAPS-UCSC, I can do that, too.

Accurate tagginig is what OSM is about.  Should mountain bikers decide to trespass by mountain biking here, the risk in doing so is wholly on those who choose to break this law.  In short, maps don't make people trespass, trespassers decide to trespass.

And, conclusively, access=permissive is now known to be wholly incorrect.