Nice page - wondering about the intro portion where Front Range is said to be furthest east in CO - the Spanish Peaks are further east than Pikes, and Fishers Peak is four quadrangles east of the Spanish Peaks. The relief of the Front Range is not unique - the Sangre de Cristos also have this on the east side.
Traditionally the Front Range southern border is the Pikes Peak Massif. I agree that the "Greater Front Range" covers Spanish Peaks and Fishers Peak (also pointed out by Noel & Fielder in a book Colorado 1870-‐2000 Revisited: The History Behind the Images). I recently finished the Front Range Atlas, called "Eagle’s View of the Front Range" that covers those. You may download a pdf file of it from http://pikespeakphoto.com/aerials/front_range.html Note: it's a 53M file: 572 pages.