Cutthroats are found across a broad range of the western United States. Historically, they emerged as soon as the uplands on the eastern slope of the Rockies cooled water sufficiently.
Today, “cutts” survive principally in headwaters and other isolated pockets of the western US. In lower streams, a combination of habitat degradation and competition with exotic species has greatly reduced their populations.
Source: Map by WildTroutStreams.com with distribution from multiple sources (see individual variants)
Below: Same map, zoomed down to Level 14, with USGS National Topo Map as basemap, showing details for Rio Grande Cutthroat Conservation Population. You will need a pointing device to show this information.
*Note: Coastal Cutthroat Trout streams are not documented sufficiently to include on the webmap. However, some of the best available information can be downloaded from this site. See: Coastal Cutthroat.