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. http://www.natureserve.org/explorer/index.htm
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. http://www.cnhp.colostate.edu/
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. http://plants.usda.gov/java/
Southwest Colorado Wildflowers - Colorado, New Mexico, Arizona and Utah (excellent website) http://www.swcoloradowildflowers.com/index.htm#top