If this tile is 600 miles across and say 1200 pixels then each pixel is half a mile. We measured mountains and found that they average at about 7 miles across but some in Chile were larger but only up to about 15. So somewhere between 15 and 30 pixels is about the size of a mountain.

So I think that I need to process a little more. The raised ground is mountainous areas in general and need to be blended with a 15-30 pixel noise map to give a mountain range in that shape. A kind of bump map there, a little different from what you said but much the same.

Then I need to run the process a bit more and let the rivers sync up again for the new mountainous regions. I wasn't planning on having any snow here in this region but I could leave a little sprinkling on top if you think it would look nice.