Mike Gage, a North Bay legislator in the 1970s, close associate of former Gov. Jerry Brown and a globe-trotting whitewater rafting guide, died of cancer Monday in Salem, Oregon, where he had become an organic farmer. He was 76. Gage, who grew up in Napa and served two terms in the California Assembly, from 1976-80, had a varied career that included serving as Los Angeles deputy mayor and chair of the powerful L.A. Department of Water and Power Commission and the Metropolitan Water District of Southern California.