George tells Lennie to come and hide in the bushes near where they are camping in Chapter 1. He will come and find Lennie there and tell him what to do next.
"Look, Lennie--if you jus' happen to get in trouble like you always done before, I want you to come right here and hide in the brush."
"Hide in the brush," said Lennie slowly.
"Hide in the brush till I come for you. Can you remember that?"
That is exactly what Lennie remembers being told and what he does after he accidentally kills Curley's wife in the barn. George understands what happened and knows where to find Lennie, so he is able to get to him before any of the other men do. They would be sure to locate him because there are so many of them and they have a dog.
The novel was made into a successful New York stage play in 1937, the same year it was published. It seems that Steinbeck was deliberately structuring the novel with the play in mind, because there are very few "sets," and these sets, especially the bunkhouse, are very simple and constantly reused. One of the simple sets would be the campsite in the opening chapter. The story and play both begin there and end there. For a stage play the setting would only require some trees and brush painted on a backdrop and an electrically lighted "campfire" in the foreground.