Would the three bars on his sleeve indicate the length of service on the UP?

The Union Pacific had both passenger trains and locomotives called Challengers. As far as I know, the two were not necessarily associated with each other. A Challenger (locomotive) might pull a Challenger (passenger train) over part of the trip.

He's holding a standard flagging kit, the larger diameter tube in the foreground holds fusees (flares to some), the smaller diameter tube on the far side holds the flag when not in use. Like many trainmen, he has wrapped a number of track torpedoes (explosive devices that make a very loud sound when a train rides over them, but don't damage the track or wheel) on the smaller tube to make them easy to get to.

That container could be holding flares or railroad torpedoes.

This man is standing on the roadbed the Central Pacific built for the transcontinental railroad, which met the Union Pacific north of Salt Lake City. Southern Pacific acquired the Central Pacific through land leasing in 1885. Union Pacific purchased Southern in 1998.

Vest watch, creased trousers, shined shoes, with a shave.

What is he holding in his left hand?

The Challenger passenger trains were really jointly operated by three railroads. The Chicago & North Western, the Union Pacific, and the Southern Pacific.

The route through Carlin was off UP track, and onto the SP's. I spent some time in Carlin, not long after this shot was made, and I can tell you that the trains passing through town were almost certain to be the daily highlight to a young boy. Glad I like trains, I was.

[Our brakeman is wearing a UP uniform. - Dave]

What you write eventually was true. But, in the time of the photo, and during my youth, the shared track was owned by the Western Pacific, and only came under the UP's ownership when they absorbed the D&RGW, which had earlier gobbled up the WP. Of course, it all belongs to the UP now.

I don't know the operating arrangement, but it could well be that the UP supplied through crews for the train.

[Before Union Pacific acquired Southern Pacific in 1997, the two railroads operated separate tracks across northern Nevada. Between Weso, just east of Winnemucca, and Alazon, to the east of Elko, UP and SP operated dual trackage, with westbound traffic moving on one line and eastbound on the other. More on the Union Pacific Challenger. - Dave]