On the other hand, the effect of this situation on the most prominent point in a county is much greater. Although all points of earth in proximity of a high point are almost as high, the same cannot be said of prominence. Since high prominence is ascribed only to the exact mathematical point that represents the highest ground, all other points on the surrounding slopes get zero prominence. Thus, if the exact summit is exclusively in one county, the other county, even though it reaches very close to a very prominent summit, cannot lay claim to any significant prominence in the vicinity of that summit, and the most prominent point in the county lies elsewhere.
Consider, for example, Mt Whitney, which lies on the border of Inyo and Tulare counties in CA. If one argues that the summit of Whitney is 1 foot inside of Inyo county (a hypothesis not ruled out by even the best topo maps), then Tulare county loses out on the prominence of Whitney, and the most prominent point in Tulare county becomes Kern Pk. On the other hand, if one argues that the summit of Whitney is 1 foot inside Tulare county, so that Inyo county loses out on Whitney's prominence, then the Inyo county prom champ becomes Telescope Pk. A purist peakbagger would argue that one must climb both Whitney and Kern in order to claim to have been to the most prominent point in Tulare county, and that one must climb both Whitney and Telescope to claim to have been to the most prominent point in Inyo county.
The rule dealing with county prominence points on or very near a county line is not quite this strict. If one might argue, as is the case for Mt Whitney, that the summit could be on either side of the border, that is taken as evidence that the highest ground is exactly on the border, and that both counties can lay claim to the prominence. In other words, an alternate peak is never listed for both counties, in case the exact summit is on one side of the border or the other, and a peakbagger cannot be required to climb an alternate peak in both counties.
If, on the other hand, it is clear which side of the border the summit is on, if it is not exactly on the line, then an alternate peak may be listed for the county that might lose out on the prominence of the summit. This is the case for Mt Thielsen, which is very close to the border of Douglas and Klamath counties in OR. The topo map shows that the exact summit of Thielsen could be exclusively in Douglas county. Klamath county would then not have claim to the prominence of Thielsen, and that county's most prominent summit would then be Yamsay Mtn, some 35 miles SE.
It is interesting that there are at least two instances in which the same peak, lying very close to a point where three counties converge, simultaneously serves as an example of both types of cases. In CO, Blanca Pk is exactly on the border of Alamosa and Costilla counties (so that both may claim Blanca's prominence), but a third nearby county, Huerfano, probably loses out on account of not quite reaching the summit. In NC, Watauga and Avery counties can definitely lay claim to the prominence of Calloway Pk, but it is not clear from the topo maps if nearby Caldwell county reaches the exact summit; hence an alternate peak is listed as the Caldwell county prom champ.
Some examples of cases in which a summit is exactly on a county line, so that both counties lay claim to its prominence, are:
| Counties | Summit |
|---|---|
| CA Inyo & Tulare | Mt Whitney |
| OR Clackamas & Hood River | Mt Hood |
| OR Jefferson & Linn | Mt Jefferson |
| UT Juab & Utah | Mt Nebo |
| OR Deschutes & Lane | South Sister |
| CO Alamosa & Costilla | Blanca Pk |
| TN Sevier & NC Swain | Clingmans Dome |
| CO Huerfano & Pueblo | Greenhorn Mtn |
| CA Alpine & El Dorado | Freel Pk |
| NC Avery & Watauga | Calloway Pk |
Some cases in which a summit may lie exclusively in one county are:
| County that can definitely claim the prominence | Summit | County that may lose the prominence | Alternate summit |
|---|---|---|---|
| CO Alamosa & Costilla | Blanca Pk | Huerfano | Greenhorn Mtn |
| OR Douglas | Mt Thielsen | Klamath | Yamsay Mtn |
| NC Avery & Watauga | Calloway Pk | Caldwell | near Cottrell Knob |