First published in 1913, The Heart of the Hills is the last novel completed by John Fox Jr. and the final piece in his mountain trilogy. This companion to The Little Shepherd of Kingdom Come and The Trail of the Lonesome Pine is crucial to an understanding of Fox's views.

In The Heart of the Hills Fox revises his earlier thoughts about mountain people. He depicts more clearly than in his previous work just how they were exploited by outside industrialists-those men who, in the words of Fox's hero Jason Hawn, "got rich diggin' our coal an' cuttin' our timber." He also reveals the long-term impact of this exploitation on the environment. Having witnessed the ravages of clearcutting on his travels through the mountain country of Kentucky and Virginia in 1911-1912, Fox was all the more receptive to the warnings voiced by his environmentally conscious father. From their letters and diaries it is clear that John Fox Sr.'s influence permeates The Heart of the Hills; in this work, dedicated to his dying father, Fox determined to make amends to the mountain people.