Officially, there are two mountain ranges in Jefferson County: the Elkhorns and the Boulder Mountains. According to the U.S. Board of Geographic Names, which only recognizes the aforementioned in our county, a range is “a single mass of hills or mountains.” Simple, and not particularly useful.
There’s also the concept of a subrange — smaller collections or offshoots of a larger range not distinct enough to be their own. What makes a mountain range and separates it from another is part relief, part geology, part adjacent barriers (such as a river), and part the circumstance of having someone officially name it. The Bull Mountains of Jefferson County have all of the former, but none of the latter.
Rising nearly 4,000 feet above the valley floor, Bull Mountain is a gigantic mass of earth 8,600 feet in elevation just south of Boulder. The U.S. Geological Survey, classified it as a ridge and not a summit. Ridges and summits overlap in their definitions, and so characterizing that prominence as either figures just fine.
