Detailed map showing the explorations and surveys in search of the best route for the transcontinental railroad through the Rocky Mountains to the Pacific Ocean.
The map appeared in Volume XII of the United States Pacific Railroad Surveys, a comprehensive work compiled over the prior decade in aid of the government's attempts to encourage the construction of Transcontinental Railroad lines.
The map reaches from the Snake River and the Rocky Mountains in the east to the coastline between the Columbia River and Puget Sound, showing exploration routes, rivers, roads, topography and many Indian regions and villages, forts and towns. Unexplored regions are noted, as are observations on the terrain seen from the exploration routes, but not actually explored.
Inset: "Reconnaissance of the Railroad Route from Walla Walla to Seattle via Yak-e-mah River & Snoqualmie Pass".