Justin Hinckley Sisson's arrival in Siskiyou County is believed to have been in 1857. He had been in California for several years, mining for gold in several central California counties. He filed on government land in the area of Mt. Shasta, and built his home.
The land where the Mt. Shasta Fish Hatchery was part of Sisson's homestead, as was the area of the town of Mt. Shasta. At that time the whole valley was called Strawberry Valley. Sisson established a new home on Old Stage Road, and the enlarged it into and inn. It became very popular for tourists to spend time there in the cool summers.
The first post office was established in 1870, with Mr. Sisson as the postmaster. The name of the new post office was Berryvale. When the railroad came through in 1886, Sisson apparently donated some of his land for the establishment of the railroad station and a town, called Sisson's.
The town was incorporated in 1905, the "s" was dropped and it became Sisson. The Post Office was changed to Sisson in 1888. On July 25, 1922, by a vote of 103 to 33, the name of the town was changed to Mt. Shasta. The railroad didn't change the name of their station until 1925.
from The Siskiyou County Museum and Historical Society