The Himalayan Districts of Kooloo, Lahoul and Spiti (1871) is a landmark colonial-era survey of the Western Himalayas. Based on two years of official tours as Assistant Commissioner of Kulu, the book records landscapes, social life, and religious traditions with unusual breadth. It includes one of the earliest examinations of the vamśāvalī (genealogical rolls) of the Kulu Rajas and a preliminary study of temple architecture, making it a valuable resource for both administrators and scholars.

Although Harcourt intended to expand his research into a fuller history of Kulu, only this official report appeared in his lifetime. Later historians drew heavily on his unpublished notes, ensuring his observations remained central to the study of the region.