I'll nominate PLAINSONG by Kent Haruf (301 pp, 1999)
Per Library Journal, "Two bachelor farmer brothers, a pregnant high school girl, two young brothers, and two devoted high school teachers--this is the interesting group of people, some related by blood but most not, featured in the award-winning Haruf's touching novel. Set in the plains of Colorado, east of Denver, the novel comprises several story lines that flow into one. Tom Guthrie, a high school history teacher, is having problems with his wife and with an unruly student at school, problems that affect his young sons, Ike and Bob, as well. Meanwhile, the pregnant Victoria Roubideaux has been abandoned by her family. With the assistance of another teacher, Maggie Jones, she finds refuge with the McPheron brothers„ who seem to know more about cows than people. Lyrical and well crafted, the tight narrative about how families can be made between folks who are not necessarily blood relatives makes for enjoyable reading."
Marj