From "The Passes of Colorado" by Ed and Gloria Helmuth: "We have chosen to define a pass as the point used to cross a ridge that divides two watersheds. "Divide" and "saddle" are other descriptive words sometimes used to identify passes. Most passes are the low point between two higher points and are shaped as a saddle; "divide" describes the water division. Some passes are named "gap", yet meet the criteria of a pass as given here. ... Any low spot in a mountain range could be considered a pass; however, we recognize in this book only those locations that have had use as a trail, railroad crossing, or roadway, and that have been or are known with a pass name. Other low spots are crossed with roads; however, if no name has ever been associated with such a locale, it is not listed in this work. Some passes are no longer used. If there had once been a use for such a crossings and a name had been given, those passes are included. Now, what a pass is not. A pass is not a gap - a gap is not a pass. A gap is cut through a rock or mountain barrier that has usually been formed by water. A gap has no watershed division associated with it; rather, the same watershed is present on both sides of the gap."

From "Hiking the Highest Passes of Colorado" by Bob Martin: "Besides the passes with official names, there are many passes in Colorado that are known by unofficial names. Such names are not shown on the United States Geological Survey topographic maps and have not been approved by the United States Board on Geographic Names. However, such unofficial names often are used in reference books and may be common in local usage. Consequently, many of the passes with unofficial names are better known than some passes with official names."