The term is "adverse possession". The period
of time varies from state to state. The public swimming beach near our
place in WI had an access where no right of way had been recorded. After a
lengthy court battle the public got the right of way. In WI you had to
prove 25 years of continuous use in this particular case.
In NJ during the 30-40's the Prudential Insurance
Company building featured a public walk way through it (with no stores).
The company would close this to the public one business day every 7 years to
prevent loosing the right to close it at any time.
Ed
PS. Not legal advice, your mileage may vary,
avoid excessive use, professional BS'er.
Ed & Wendy Hauser 2994 Mittower
Road Victor, MT 59875