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I just looked it up.  You can see them from Nebraska (on a clear day), which is about an equal distance away.  But between Kansas and the Rockies you'll find Denver, the "mile high city".  Both topography and atmospheric conditions make a difference.  There could be a thousand foot mountain 10 miles away, but if I have a 100-foot tall building 50 feet away in between me and the mountain, I won't see it.  It has to be asceratined, based on what's in between, whether there should be a line of sight.  And then even with a direct line of sight there are limits to how far you can see through the atmosphere.

We can see the moon, and it is over 200,000 miles away.  Topeka, KS, is only 600 miles away from the Rocky's.

So my stands: If the Earth is Flat, why can you see the Rocky's from Topeka, KS, using a telescope? 

You're a bit late to this debate.  No, the moon is not 260,000 miles away (as is claimed).  There are lots of reasons for that, but that's been discussed before.

IF there were no atmosphere and you can prove that there should be a line of site (given the topography BETWEEN the two points), then there may be some proof there.

Even if we grant for the sake of argument that the moon is 260,000 miles away, #1) we clearly have a line of sight to it, and #2) it's enormous ... so it's impossible to miss.  Occasionally I see an interesting moon that super huge in the sky and a different color, as I'm driving around, and I remember being upset because I lose line of sight to it (because it was still relatively low) due to trees, buildings, or other obstructions.

So for your example to prove anything you'd have to prove that we should have line of sight to it given the topography.

#2, there are limits to what you can pick up with photography/telescopy.  Using the same types of optics that telescopes use, the world record for long distance photography is about 230+ miles (if I recall), and even the mountains that are picked up are barely visible and extremely blurry due to the atmosphere in between.  Westernmost part of Kansas to the Rocky Mountains is about 800 miles (looking at Google maps).  So to be able to see it would be to quadruple the world record for long distance photography, which just BARELY picked up stuff from about 230+ miles away (due to an atmosphere).  And those long range photos are rare ... because we have something called an atmosphere.

Now, you could claim.  Well, we can see the moon through the atmosphere  #1, it's absolutely enormous compared to a mountain, #2, it's a very bright and luminous body (unlike a mountain), and #3 we dispute that it's 260,000 miles away.

In sum, if you could get rid of the atmosphere and we could prove that there should be line of sight based on the intervening topography, then your point might have some probative value.  As it is, it does not.

In the meantime, FEs have produced literally hundreds if not thousands of images and videos showing objects that should not be visible if the earth had the curvature that's claimed.  And "see too far" is just a tiny piece of the puzzle where it comes to Flat Earth.