From the Herald Times in Colorado:
Gray wolves were eradicated from Colorado by the 1940s to protect domestic livestock, but groups like the Sierra Club are working to change public perception of wolves in hopes of reintroducing the animals to their former habitat. United States Fish and Wildlife Service has restored wolf populations to Wyoming, Idaho, Montana, New Mexico and Arizona. Colorado is the last holdout. A few wolves have migrated into Colorado’s North and Middle Park, but the animals haven’t been officially reintroduced, largely due to continued opposition from livestock producers and hunting organizations.