 In the 1870s, the area that would become Thorp was known as Pleasant Grove and was part of Yakima County.On July 6, 1872, the Pleasant Grove post office on the west side of the Yakima River was established at the ranch of John S. Vaughn, and the Taneum post office was discontinued the following year on April 7 due to an unnecessary overlap in service.Despite being one of the earliest locations in Kittitas County to be settled, Pleasant Grove would remain sparsely populated for the next decade, with cattle ranching as the primary occupation.