One theme in "Up in Michigan" has to do with gender roles. Liz Coates is a sheltered, subservient young woman who looks to others for cues about how to conduct herself. Though she is attracted to Jim Gilmore, she does not make it known to him until he makes the first move. She is so repressed that she dares not even bake for him for fear that Mrs. Smith will discover her feelings.
Jim Gilmore is "a man's man" who does physical labor, goes hunting, drinks whiskey, hangs out with other men, and, when he decides he wants to, has sex with Liz. He is thoughtless and crude, whereas Liz is sensitive and caring, evidenced by her gentleness toward Jim after he passes out after having drunken sex with her.
Liz's experience brings in perhaps another theme: disillusionment. Liz feels disillusioned as she undergoes the rite of passage of losing her virginity to Jim, passing from innocence to experience. To her, the initiation of the sexual act is the culmination of her feelings for Jim. As for Jim, there is no indication that what happens with Liz is anything more than a lustful act that reads as rape, since Liz does tell him, "You musn't do it, Jim. You musn't," to which he responds "I got to. I'm going to. You know we got to."