[nprecup]

You can see the sisters from Mt Adams, which is ~230 km away. I'm guessing there are several more of these that the site didn't catch. You can probably easily see Mt Rainier from 300 km+ standing at the right place. How were these determined? It would cool to see a write up on how it was done.

[jmcqk6]

I know you can see Mount Rainier from Mary's Peak outside of Corvalais, which is 295km away. And I mentioned it in another comment here, but standing on paulina peak on a clear day, you can see both Mount Adams and Mount Shasta, more than the entire height of Oregon.