This is an HDR image manually composited from two exposures - one for the sky and one for the rest of the image.
You may remember seeing a telephoto image of the same sunset earlier in the Glacier National Park gallery. It takes a lot of time, effort and cost to get to places like this. Sunrises and sunsets do not last long and often yield the best images of the trip. So, I often have two tripods and cameras setup at these times. Especially when exposure times get long, I can nearly double my take-home from a shoot.