Katherine Darrow’s ‘Wild About Wildflowers: Extreme Botanizing in Crested Butte, Colorado‘ is another unique field guide to the wildflowers of the southern Rocky Mountains.

Nature Serve is a great site, and an authoritative source for information on more than 70,000 plants, animals, and ecosystems of the United States and Canada. Explorer includes particularly in-depth coverage for rare and endangered species. 

The Colorado Natural Heritage Program is Colorado’s only comprehensive source of information on the status and location of Colorado’s rarest and most threatened species and plant communities. 

PLANTS Database is another very helpful website. It provides standardized information and photos about the vascular plants, mosses, liverworts, hornworts, and lichens of theU.S. and its territories.

Southwest Colorado Wildflowers – Colorado, New Mexico, Arizona and Utah (excellent website)