Mossyrock sits on the eastern edge of Klickitat Prairie. Although the prairie was named after the Klickitat Indians, it was actually home to the Taidnapam, or Upper Cowlitz Indians, and both groups spoke a dialect of Sahaptin. Early settlers often confused the Taidnapam with the Klickitat because the languages sounded similar. Klickitat Prairie was once considered the entrance to the land of the Taidnapam, and today it is the gateway to East Lewis County. East of Mossyrock, the highway parallels the Yakima-Cowlitz Trail, a historic route connecting American Indian settlements east and west of the mountains and the principal route used by settlers into the valley from about 1855 to the 1890s.