Answer:
Step-by-step explanation:
It says that Balboa is dragging the responsibility of building or developing this civilization up the pure and unspoiled (as in neat and clean and fresh) slopes, over the mud and leaves. Meaning that it's considered heavy and difficult since he doesn't trust people so he refuses to have companions to help him out throughout the process. Balboa was making history and building an extremely effective civilization that would affect him and all Indians and the whole history, alone.