This has been brought up before and hashed over ad nauseam, including this document.

Cut and pasted directly from the document: "In 1987, Alameda County acquired the entire line from Niles to Tracy rather than allow full abandonment."

Did the county purchase it outright? Never heard nor seen documentation which explicitly says this, here nor anywhere else, nor have any links to such a document been posted. The legalese and processes connected with R/W transfers to rails to trails is complex and dense, all too easily misconstrued by the "layman". But control of the R/W ultimately remains under the Department of the Interior, which I notice this document is addressed to.

"This was done to preserve the right-of-way for potential future transportation corridors."

Which is precisely the purpose of the rails to trails act. Why would the county pay gobs of money to buy the right of way outright when all it needed to do was pay the less expensive fees and jump through the hoops to become custodian under rails to trails?

Being custodian under rails to trails is tantamount to ownership, but is not ownership in the strict, legal sense of the word. WRM is in the same boat, although it's also the R/W custodian, which NCRy is not.