"The most difficult stewardship is yet to come," was the final sentence in biologist Fred Gehlbach's 1981 book about the troubled natural history of the U.S.-Mexico border region. Mountain Islands and Desert Seas was the result of Gehlbach's years of study, travel, and intensifying dismay over the continuing development and degradation of a beautiful land where jaguars, grizzlies, and bighorn sheep once roamed. Today, the environment for environmentalism...