The cavers are supposedly following Sarah's route of escape from the cave. If so, why are there no tracks (and massive amounts of cobwebs to brush away), and why did Sarah bother to nail up authentic old "Keep Out" signs behind her?
She got flushed out of the cave system through an underground stream that lead into the river. The dog only picks up her scent until the river. He probably picked up another scent which lead him to the elevator shaft. It's all in the movie.
Why was the partially eaten body of the one girl left by the entrance? We already know that the Crawlers drag off their food to store it in a more convenient location.
Why, upon suddenly remembering the events of the first movie, does Sarah run deeper into the caves, despite there being nothing preventing her from leaving the way they'd come?
There was a cave in, and the way they came in had been blocked off.