This past August, I attended the Sunsets and Stars in Rocky Mountain National Park workshop led by Glenn Randall. Among other things, Glenn instructed the participants to combine separate exposures for the sky and land to produce an appealing single image. Glenn no longer leads workshops, but I strongly recommend his book, Dusk to Dawn: A Guide to Landscape Photography at Night for detailed guidance regarding the best techniques. On a related note, I found The Ridgeline Hotel to be a great place to stay in Estes Park, adjacent to Rocky Mountain National Park.