LASSITER WAS A GUNMAN WITH A FEARSOME REPUTATION
- AND A MIGHTY VENGEANCE TO FULFILL.

Jane Withersteen was the richest woman in Cottonwoods, a peaceful Mormon village on the Utah frontier.  But now her fortune was in danger, for the churchmen wanted her to marry grim, arrogant Elder Tull.  Then they would control Amber Spring, the precious water that gave verdure to the wild purple wasteland.

When their methods of persuasion turned ugly, Jane was near despair.  But then Lassiter rode into town and strapped on his famous guns - to teach the angry mob a lesson about freedom!

From librivox.org:

The Rainbow Trail is a sequel to The Riders of the Purple Sage. Both novels are notable for their protagonists' mild opposition to Mormon polygamy, but in The Rainbow Trail this theme is treated more explicitly. The plots of both books revolve around the victimization of women in the Mormon culture: events in Riders of the Purple Sage are centered on the struggle of a Mormon woman who sacrifices her wealth and social status to avoid becoming a junior wife of the head of a local church, while The Rainbow Trail contrasts the older Mormons with the rising generation of Mormon women who will not tolerate polygamy and Mormon men who do not seek it.