sentence: Tunnels can go down as far as , and can extend laterally as much as .
sentences_before: Prairie dog tunnel systems usually have several rooms.
sentences_after: Prairie dogs line their burrows with grass to insulate them, and the earth excavated from the burrow is piled up in mounds around the burrow's entrance. The prairie dogs use these carefully maintained mounds as observation posts.
concept_name: tunnel
headings: Prairie dog Biology and behavior
categories: Squirrels