In the 16th and 17th century there were many white spots on the maps (especially around Antarctica). On the other hand: 25000 meter high mountains are visible from very far away, but they may be mistaken for lower mountains that are closer.
The physicist in me wants to know from what material these mesas are formed. Granite on an earthlike planet can reach up to 20000 meters (it can be calculated using only the melting enthalpy and the local gravity) and that is without erosion grinding it down. My best guess would be pure diamond (not sure about melting enthalpy but it should withstand erosion quite well)...