By putting the question on it’s head and allowing them to answer it themselves by their own prose.
Like “why is the cat outside?”
You could respond “why shouldn’t the cat be outside, it’s a very delightful day this evening?
I don’t think it’s a run-on sentence (might be wrong) because it has a subordinate clause and when taken out everything makes sense?
So yeah, I think it isn’t a run-on sentence.
There were no roads or automobiles in the area.
It's clear through the passage that there are no paved roads or cars to get the miners from place to place. They had to carry all of their gear and supplies through dangerous trails by foot, only being able to travel a certain amount each day.