Complex sentence: The boundaries of these ranchos were not established as they are in later times and predominately based on what can be understood as figurative boundaries based on just where another grant owner considered the end of their land or land or vegetation landmarks.
Split into simpler sentences: The boundaries of these ranchos were not established as they came to be in later times predominately based on what can be understood as figurative boundaries. They were based on just where another grant owner considered the end of their land, lands or vegetation landmarks.