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.
It is a simile because it is a figure of speech involving the comparison of one thing with another thing of a different kind, used to make a description more emphatic or vivid.