What did Lennie do to force George and Lennie to leave Weed?
In Chapter 1, George is frustrated that he and Lennie had to leave another job. This is in reference to the job in Weed. George says that if he was free of Lennie, he could "live so easy." He would be able to stay at a job, actually earn some money, get drunk, and so on. Then he says "Jus' wanted to feel that girl's dress--jus' wanted to pet it like a mouse-- Well, how the hell did she know you jus' wanted to feel her dress?" Lennie is drawn to soft things like mice, girls' dresses, and soft hair. But he doesn't realize how strong he is and he tends to panic easily. So, when the girl tries to get out of Lennie's grasp, he panics and holds on even tighter. We see this with how Lennie loves mice and puppies but tends to destroy them because he squeezes them too hard. This event in Weed also foreshadows the event involving Curley's wife.
In Chapter 3, George gives more details to Slim. George has to hit Lennie on the head with a fence picket to get him to let go of the girl's dress. But the girl is traumatized and claims that she'd been raped. A group of men set out to track Lennie down. That's when George and Lennie go to hide in the irrigation ditch and eventually leave Weed.