A story I read in the newspaper about trails that lace along upper Carmel River/creek, near Monterey, CA:
An equestrian ranch horse place did horse boarding and trail rides for the public. The trail laced along the river, and up through a county park. A giant loop that started from , and ended at, the stables.
A man bought a country house and acreage near there. The house had been in the continuous hands of the same family ownership for 80+ yrs, before being sold to this new owner. The new owner had all the land surveyed. So that he knew exactly where his property boundaries were (he intended to graze sheep). Much of the land had never been fenced (since it's just rolling non-descript scrub-brush land, gullies, cliffs, etc...).
As it turns out, the trail the horse use from the nearby equestrian place, went along the Carmel River passing this land. And the horses (and dog accompanying the horse riders ) spooked the man's sheep. The man studied the property boundaries, and realized that the trail encroached onto his land (albeit by only a tad). So he put up a fence that blocked the trail. This would force the riders to the other side of the creek. But which was essentially impassible at that junction. Thus .... the trail riding days were over. The horse trails, which had been used for 50+ yrs. at this point, could no longer make the seamless round loop to reach a county park, and back again.
A legal battle ensued. The new property said the people were "trespassing" (to, gasp, walk the ~30 yard tip across the very edge of his property). The horse people cried that if that one part of the trail were cut off, how are they going to get to the rest of the trail where it picks up again beyond that invisible 30 yard section ?
Since the equestrian people were affluent, and the property owner was affluent, each side hired lawyers. The case wound through the legal system.
The horse people called in a very elderly local person who could recall (and testified that) trails, commonly used by anyone and every one , had simply always traversed the creek's side at that point. And that horse riding had always ever gone on there. But the property owner's defense what plat maps that clearly showed his property went all the way up to the creek-wash edge, he had land surveyors testifying. So it was simply a case of "50+ yrs. of trespassers". And it still didn't "make it right". And he had animal experts testifying that a horse or dog "frightens" his sheep. And he had map people making maps to show the horse people alternate routes (that were silly and circuitous) to avoid this teensy stretch.
The bottom line is, that the horse people won. They showed historical egress (or whatever the legal terms are called).
So now the only thing left to haggle out is, what is "allowable" ? Prior to the new man's ownership, if you had ever asked anyone, they'd have told you the "trail is public". NOT because anyone ever got out a ruler and measured anything, but .... simply because .... well .... anyone can and does walk there.