The fragile San Pedro National Conservation Area is a migratory bird and animal corridor for more species than anywhere else in North America. At thirty-seven miles in length is the longest stretch of protected forest and desert riparian habitat left on the continent. It also contains the largest collection of ancient hunting sites and camp locations on the continent.
The Area is a remnant of ancient times, with mixed broadleaf willow and cottonwood trees reaching up to 90 feet height. It is one of the best birding spots in America, where two-thirds of inland species and 100 unique species can be observed, as well as migrating tropical birds.
Center for Biological Diversity article
Friends of the San Pedro River
GORP also contains good information