* Geologically oldest: The basement rocks, the foundation of the mountain, are generally the oldest. These are often igneous or metamorphic rocks formed deep within the Earth's crust, potentially billions of years old.
* Topographically oldest: The mountain peaks are often the oldest parts of a mountain in terms of their position. This is because erosion tends to wear down the higher parts of a mountain faster, leaving the peaks as the last remnants of the original elevation.
So, the answer depends on the context of the question!
