When Katie Joseff heard about a 12-year-old boy in upstate New York becoming a local celebrity after winning an Earth Day scavenger hunt, she knew she wanted to bring that to her hometown. Joseff, a Santa Barbara native, is soon to launch an environmental-themed scavenger hunt for a chance at a $500 prize for first place, as well as smaller prizes from local businesses along the way. It will officially kick off Saturday—the same day as the Solst…