Not sure the exact nomenclature of that coupler...but I've seen lots over the years. The slot holds a link if you need to couple up to link and pin log cars.
That is in Garibaldi, Oregon, next significant town north of Tillamook. They run on the old SP line there. Right now running the McCloud #25 Mike. Rode behind it to Rockaway Beach and back.

Interesting tender wheels. Both axles on lead truck have small wheels and very thick tires, with diameter obviously inches bigger than those on rear truck.
Lead wheelset on rear truck has large wheel and very thin tires. #4 is spoked.
Asked the questions, apparently 28" wheels are very hard to come by any more, so McCloud turned the wheel down and shrunk on thick, I don't know, 30" or bigger tires.
#3 hasn't had that done yet, and nobody has a clue as to why #4 is spoked, thoughts being they all were at one point and this is the only one left.
Over to the side is an SP Mike, rough, lead driver decoupled, missing some links.
