Chalk is a humble medium, one most of us associate with long afternoons in school. But in the hands of Mark Wagner, an Alameda-based artist, it becomes the stuff of legend: In 2008, under auspices of his nonprofit, Drawing on Earth, he guided 5,678 Alameda children in drawing a chalk pavement art project that measured 90,000 square feet; the project won entry in the 2010 Guinness Book of World Records. And for many years, he’s rocked the Youth in Arts fundraiser Italian Street Painting Festival with his chalk creations and 3D anamorphic street painting. Wagner’s images are mythic, mysterious, powerful: a white dove cradled in weather-worn hands, a winged goddess holding a blood-red shield, the dark silhouette of an eagle emerging from a man’s calm face. Wagner works not only in chalk but also in the film industry as a concept artist and as an illustrator, graphic designer, and educator. His motto? “Re-enchant the world through art” — one chalk square at a time.