US Environmental Protection Agency
Epa: Ecological Regions of North America
A helpful map of North America which color codes its 15 ecological regions. Click on the different regions for a brief description of the area.
University of Washington
University of Washington: Knights of Labor History and Geography 1869 1899
Overview of the Knights of Labor with maps showing the expansion of the Knights by color-coded time period, the number of local assemblies in each LA county, and more.