At the start of the book, Lennie and George are just coming to the little heavenly bit of the Salinas River near Soledad. They have been hitchhiking this way so that they can get to the ranch where they have been told they will work.
They are coming from Northern California, from the town of Weed. (Weed really is a town. You'd think the name is a joke, but one of my ex-students went to a junior college in Weed.)
The two men have had to leave Weed because Lennie has been accused of molesting a woman. After running away, the stopped by an employment agency that has sent them to the ranch.
John Steinbeck set many of his stories in California, specifically the area around Salinas where he grew up. Of Mice and Men is set on a ranch outside Soledad. Soledad is a very small agricultural town in Monterey County about 20 miles south of Salinas. Steinbeck spent his formative years traveling around this area and spent time with the workers who farmed the fertile valley.
The protagonists of the story, George and Lennie, are itinerate farm workers who are seemingly forever moving from place to place because Lennie, who is mentally challenged, often does "bad things."
They have traveled south from the small town of Weed in Siskiyou County at the foothills of the breathtakingly beautiful Mt. Shasta. The men were doing farm work when Lennie saw a girl in a red dress. He is drawn to soft and bright objects which he likes to touch or stroke. His obsession is to "tend rabbits." He scares the girl and George describes the immediate aftermath of the encounter:
“Well, that girl rabbits in an’ tells the law she been raped. The guys in Weed start a party out to lynch Lennie. So we sit in a irrigation ditch under water all the rest of that day. Got on’y our heads sticking outa water, an’ up under the grass that sticks out from the side of the ditch. An’ that night we scrammed outa there.”
On there way south from Weed, the men stop in Salinas at an unemployment office and receive "work cards" and bus tickets which bring them to the small ranch, further south, near Soledad where the principal action of the story takes place.