There are plenty of public lands in CA where you can walk around off trail.
Living soil which can be destroyed by footsteps. Cyanobacteria and lichens and algae. One of the oldest organisms on Earth.
There are plenty of places where just having visitors regularly hike across the ground off-trail does significant damage to the ecosystem, which is why fragile or popular parks restrict public access to marked trails and designated campsites.
California has 199,490 km2 of protected public lands, more area than 2.5 Scotlands.
for example, although the summit of berryessa peak is on BLM land, the only access is through private land. fortunately one land owner was convinced to allow an easement on a short section of trail to allow the opening of the berryessa peak trail, and access to this peak, but for years it was public and yet off-limits.[1]
on the west side of lake berryessa, cedar roughs wilderness, currently has no access. there are old roads/trails in there which are accessible from private land, but no public easement.
there was an article posted here last year about similar issues surrounding the crazy mountains in montana[2].
[1] https://www.summitpost.org/berryessa-peak/766290 [2] https://www.bloomberg.com/news/features/2017-10-25/this-land...