I've got a photo of what I think is a postcard showing the train depot in Mertzon, Texas:
I'm wondering what the likely date is?
The railroad started service in Mertzon in 1911. So that's the oldest your station can be (give or take a couple of years).
Your goal now is to find out when it was actually built and if it was rebuilt. Years other features were added. And also see if you can find pictures of it at various times and compare the wear.
Turns out part of it was rebuilt.
On Feb. 28, 1938, a tornado blew the south warehouse down and took the roof off the railroad depot. (ref)
Find pictures of that roof before and after 1938 and that will tell you if the postcard comes from before or after that time. Then keep going.