According to the book
The Continental Divide Mountains of Colorado's Rabbit Ears Range-A Mountain Climbing Guide and History; the Rabbit Ears Range extends from the meeting of the Park Range on the west and the Never Summer Range on the east. Both Rabbit Ears Peak and Baker Mountain are included as part of the Rabbit Ears Range, though Rabbit Ears Peak is where the Park and Rabbit Ears ranges meet (according to the book). The history part of the book credits Clarence King in defining the boundaries of the Rabbit Ears Range in his 1871 and 1872 surveys and cites King's
Geological and Topographical Atlas of the Fortieth Parallel published in 1876. Perhaps this makes some sense because Rabbit Ears Peak itself is a volcanic plug and most of the other peaks in the Rabbit Ears Range are volcanic as well, unlike the Park and Gore Ranges (unless Rabbit Ears Peak is included in those ranges).
The book
History of Routt County credits Rabbit Ears Peak as the meeting point of the Park, Gore, and Rabbit Ears Ranges.
The topo maps also seem to verify that the Park and Gore Ranges do indeed meet at Rabbit Ears Peak.
Notice that the topo map definitely show that the Gore Range extends north of US 40 and north of any saddle:
Also notice that Rabbit Ears Peak is roughly half way between the words "Park Range" and "Gore Range" and that the labeling of both is very near the peak.
Although some are looking for a saddle to define the boundary of the ranges, it appears that the boundary of the ranges is Rabbit Ears Peak itself although except for perhaps the Rabbit Ears Range it remains unclear as to why a peak was chosen as the boundary of the ranges (though the two ranges are merely named different; geologically the Park and Gore Ranges are one and the same and part of the "Greater Park Range").
Edit and update:
I was able to find the
Report of the Geological Exploration of the Fortieth Parallel online, but not the referenced
Geological and Topographical Atlas of the Fortieth Parallel online. In the former it mentions Rabbit Ears Peak as part of the Park Range study and says that the Park Range was named by James T Gardener. It also says the termination of the range is at Pelham Peak on the north, but I haven't gotten to where it says the southern boundary is. I also can't figure out which peak Pelham is and find no current reference to it online or on any topo map.
Anyway, the report is 803 pages long and it might take a while to skim through.