Today we still use railroad spikes worldwide but finding some from the old days is always fun.
Here are a few we have collected up over the years.....the center one was just found this week near Antero junction, Colorado. And cool it is.....it's a narrow gauge!
The three pictured here are
Bottom- Standard guage (5 1/2" - 9/16" shank)
Center- Narrow gauge (4 1/2" - 1/2" shank)
Upper- Narrow gauge (2 1/2" - 5/16" shank)
Narrow gauge often being used in the mountains back then as they didn't need as wide of a track or area cut into the wilderness.
They hauled smaller loads which to some degree was an advantage in the mountains as well.
The smallest of these spikes would have been used most likey in a mine for ore carts rails....also called narrow gauge.
Here is a link that shows the different sizes and how many came in a 200 lb keg which is how they are sold.
http://www.sizes.com/tools/spikes_railroad.htm