This Calder Sky by Janet Dailey

The Calder Cattle Company is a huge ranch in Montana. Chase Calder is heir to this booming industry and everyone knows who the Calder family is, and their word is law. With water and grass depending on the weather and the survival of the herd the focus of the ranchers, Chase has his work cut out for him. When others seek to use his grass and water, trouble is on the horizon. Neighbor Maggie O'Rourke, only a teenager and motherless, father a ne'er do well, falls under the spell of handsome, rugged Chase. But Maggie is determined to make something of herself. Not wanting to become another rancher's wife, she heads to California to educate herself and make her way in the world. An amazing tale of life on the plains, in Montana's rugged country. A good read.