During the part where the president is trying to hammer the stake in for the Union Pacific railroad, notice the flags flying behind him. They are current flags with 50 stars! If this takes place in the 1800's, there are not 50 states!
Not to sound to arrogant but I noticed the same thing in Young Guns a while ago. Check out slipup entitled American Flag. It's always great when someone slips up that bad.
Actually, to be even more specific:
1803: The United States purchases the Louisiana Territory from France
1867: Nebraska admitted to the Union, the US flag now has 37 stars
1869: Setting for the movie Wild Wild West (flag should still have had 37 stars)
1959: Hawaii admitted, the flag gets its 50th star
If you want to see a drawing of the flag they SHOULD have used in Wild Wild West, go here: http://www.icss.com/usflag/the.37.star.flag.html
Gosh, imagine that, they got the flag wrong. It seems strange considering the all the effort they put into historical and scientific accuracy in every other scene. Especially with those authentic gigantic steam powered spiders, rocket powered gliders, intelligent flying killer Frisbees and let's not forget that b**chin' the recently dead's last glimpse projector machine. And then to slip up on the flag. Well, I guess nobody's perfect. You really *NAILED* them!