Question

Using rates of erosion to determine absolute age is only practical for geological features

Answer 1

Using rates of erosion to determine absolute age is only practical for geological features that have not been disturbed. If the layers of the soil are undisturbed, be it by human action or natural disturbance, than the layers are sitting on top of each other and mark the separate periods of time with their characteristics, so it doesn't matter how big of an erosion has taken place, there's still remains of a certain period and determine its age.