Which is why I, and a few others, use the 100th meridian west as the line of demarcation (which runs right through Dodge City).
Without further qualification, I’d say the Mississippi River.
If you are speaking of Colonial times, then the Appalachians – and the rest of the continent – would be “out west.”
The West in terms of movies and the Old West definitely includes Texas, so anything north of there would fit. Oklahoma, Kansas, Nebraska, the Dakotas. I can’t decide about Missouri, Iowa and Minnesota. And since Arkansas and Louisiana are in the SEC, I think Southeast for them.
The Far West is basically the same (to me) as the Pacific Coast.
I’m less clear in my own thinking about dividing lines between Southwest and Northwest.
Interesting. The National Park Service, Wikipedia, and virtual every history and account of the trails themselves indicate that the trails started in Missouri, not at Fort Leavenworth.
Park Service: Oregon Trail Map, partial Santa Fe Trail map.
Wikipedia on Oregon Trail: “[T]he Oregon Trail’s primary starting point was Independence, Missouri, or Westport, Kansas City (Missouri)…”
Wikipedia on Santa Fe Trail: “The eastern end of the trail was in the central Missouri town of Franklin…”
I think my liars can beat up your liars. 
Fort Leavenworth was a “jumping off” point for the trails – the starting point for some of those who traveled them. No way was it the easternmost point of the trails.
Somewhere between Houston and Dallas.
Western South Dakota was definitely Old West if you are thinking in terms of cowboys and Indians, rootin’-tootin’ and such. Wild Bill Hickock and Calamity Jane are both buried there.
But immediately west of the Mississippi I think of as prairie and farming folks. Central Minnesota is where The (ahem) Indian Uprising took place in the mid 1860s complete with massacres so I suppose you could consider that the Wild West though it was much more an agrarian and domesticated society at the time than farther west.
Pittsburgh isn’t part of the midwest, either. It’s the north east. We have some cultural similiarities, but we’re certainly not the midwest.
Are you sure you didn’t just hear Pittsburgh referred to as western PA? (We generally devide the state between Pittsburgh and Filthadelphia)
I’d place the starting point at the first mountain range west of the Great Plains, or where the topography first changes. This would be the Rockies in Colorado, the Wichitas and Balcones Escarpment in Oklahoma and Texas, and perhaps the Black Hills and Badlands of the Dakotas.
Maybe we could use a map of the US at the Centennial as a basis. The West is all territories and disputed areas; California, Nevada and Oregon, and Texas west of the Balcones fault or the Chisolm Trail. Basically, the areas that were beyond the borders of the time. This would also match up with the start of the settlement of the West.
Several people in this thread seem to disagree but for me the divide is the Mississippi.
I agree with Gary. I grew up in Kansas City, which meant numerous field trips to Independence, history lessons on the various Trails, placards near my home for the Santa Fe Trail (which was decidedly east of Ft. Leavenworth), etc.
The Mississipi is just a little too far east to be the dividing line, imho. I’d say it’s about midway between the Mississippi and the Missouri, or roughly 2/3rds of the way west across Minnesota, Iowa and Missouri. This is also about where the Plains proper can be said to start. Kansas is definitely in the West, although if there’s such a thing you would have to call it the “eastern” West. 
I do believe you misspelled Pissburgh. 
Said by whom? GaryT provided three maps of the Plains in the thread linked in the OP, none of them come close to touching Missouri.
I defy anyone who’s ever visited southwest Minnesota to say it isn’t “the Plains”. And any region that fought a war against the Dakota Sioux is the West.
I’ll throw my vote in for the 100th Meridian West.
I’d agree with this. I first thought “the eastern border of Colorado extended north and south,” but then I figured it had to include Dodge City.
I’d actually expand the northern point up to Omaha, Nebraska. Pretty much anything west of that line is…well, it’s The West.
It’s important to ask, “when?”
“The West” certainly began at St. Louis onceuponatime, since most everything west of it was “uncivilized” to Easterners. Later, Denver was the boundary. As settlements moved in, the West moved west, and eventually merged with the West Coast moving east.
I’m in agreement with the Census Bureau maps linked above, with the exception of Maryland, Delaware, Texas, and Oklahoma. MD and DE aren’t southern states, and OK is more of a Midwestern state in my eyes. Texas is the big question mark to me as it definitely fits in with the West but probably self-identifies more with the South. There’s probably a point somewhere in the middle of Texas that marks where the “West” begins, and OK, KS, NE, and the Dakotas aren’t in the West.
Also worth noting, I think, is that when I think of the “West” I don’t include any of the Pacific Coast states, as they seem different enough to warrant their own division. FWIW I was born and raised in Arizona.
I would go for this. The Great Plains are the middle. Anything to the west of them is in the West. Anything to the east is the East. Or an alternative could be the 20" rainfall line. That would leave the Dakotas and the western 3rd of Texas in the West. Certainly any state that was already connected by rail to the original 13 states by 1860 should be out. In any case, any rule has to leave Minnesota, Iowa, Missouri, and Arkansas out of the West. Geographically, climatologically, & culturally none of them fit. So the Mississippi doesn’t work as a divider.
Of course you should take that with a grain of salt. I think some traditional names need to be changed, namely the Midwest. Hate to tell people this… but if you look on a map the “midwest” of the continental US (i.e. the middle of the west) is Utah-Colorado. And this has been the case for well over 150 years. It is time to let the name retire and quit referring to Ohio as the Midwest.
The more I think about it, the more I think that’s a reasonable line of demarcation.