Going though some boxes in the basement, I ran across a Breckenridge trail map from the 78-79 season. Find the rates scanned in the first image. (You may have to click on the image to make it more readable.) The mountain map is below the rate and skiier information. Notice there were only two mountains to ski some 30 years ago.
Compare the image above to what is available to skiiers now. Below is an image from the Breckenridge website.