Tyrone Mill, Sonoma Co., Calif. March 10, 1878

It appears this list is all Sonoma County, Calif. post offices. I'm guessing the name in the second column is the new postmaster, or the outgoing pm in the case of Skagg's Springs.
Between the two original Tyrone entries, I notice the change from Austin (5 Aug 81) to Ingram's (23 June 86) which became Cazadero, the end of the NPC RR line.

Austin 8/5/81 - 6/23/86 to Ingram's 6/23/86 - 4/24/89 to Cazadero 4/24/89 - open.

I trimmed the page down to just show between the two entries for Tyrone.

Shows when postmasters changed and when office discontinued.

This is where I've been finding the info. Takes a bit of hunting as the film pages are not searchable, but there is a lot of information if you look.

Records of the Post Office Department, 1773–1971
https://catalog.archives.gov/id/357

pat
P/S - can also find other counties and states.

Hopefully, all those pages will be digitized before the last of the cursive reading collectors are gone!

....For Santa Rosans and other locals, the most popular resorts – or at least, the most often mentioned in the newspaper columns – were Camp Vacation, just across the river from Bohemian Grove, and Eaglenest, location of modern-day Rio Nido....

An interesting read about the area.
http://santarosahistory.com/wordpre...lost-places/
(This same PC view as shown in the article)

I clicked on the google map thumbnail on the linked page to see it full sized. It shows a user modified google map, user added the old train stations.
Vacation appears to be very close to the nine-hole Northwoods Golf, built in 1928 by Dr. Alister MacKenzie, a famous golf course architect of the era. No doubt his selection was influenced by the folks across the river.

https://en.wikipedia.org/wiki/Alister_MacKenzie

Bring your A game! No. 8 par 5 is a monster!

A day or two after the last post here, I saw a reproduction post card of RR engine "Tyrone", a NPC engine, not listed among the rest in the roster that Pat posted on page 1.
I can't see any number on the engine, just the name Tyrone.
Here it is in front of the hotel El Bonito in Duncan's Mills, Cal. The man in the middle is Alexander Duncan, mill owner.

Here's a postcard of a small waterfall at "Park" Tyrone. Possibly the runoff from the flume?