Map with facsimile of horse dispersal from a map at: Haines, Francis. "The Northward Spread of Horses Among the Plains Indians." "American Anthropologist" New Series, Vol. 40, No. 3 (Jul. - Sep., 1938), pp. 429-437 at p. 430 online version. Depictions of the Great Basin and Continental Divide from USGS hydrographic .shp files. Depiction of the Great Plains from this map