What evidence is there that shows that man has interacted with the natural surroundings described in the beginning of the novel?

The opening paragraph of the novel describes an unspoiled, Edenic landscape with the Salinas River and the foothills rising to the Gabilan Mountains. Willow and sycamore trees rim the river, and there are the tracks of rabbits, deer, raccoons, and dogs that visit to drink from the pool.
In the second paragraph, the narrator observes the marks that men have left on the landscape:

There is a path through the willows and among the sycamores, a path beaten hard by boys coming down from the ranches to swim in the deep pool, and beaten hard by tramps who come wearily down from the highway in the evening to jungle-up near water. In front of the low horizontal limb of a giant sycamore there is an ash pile made by many fires; the limb is worn smooth by men who have sat on it.

When George and Lennie arrive, the peace and beauty of the place is further disrupted. George is angry and fills the air with profanity as he maligns the bus driver who has put them out and scolds Lennie for his forgetfulness and carelessness. Lennie carries a dead mouse in his pocket, and when George discovers it, he tosses it into the brush. Their arrival furthers the observation that mankind has difficulty living harmoniously in nature.