Clark was born in Tulsa. He learned photography at an early age. His mother was an itinerant baby photographer, and Clark himself was enlisted in the family business from the age of 13.
In his mid-teens,Clark began injecting amphetamines with his friends in 1959. Always armed with a camera, from 1963 to 1971 Clark produced pictures of his drug-shooting coterie that have been described by critics as "exposing the reality of American suburban life at the fringe and for shattering long-held mythical conventions that drugs and violence were an experience solely indicative of the urban landscape."
He attended the Layton School of Art in Milwaukee, Wisconsin where he studied under Walter Sheffer and Gerhart Bakker. He was drafted to serve in the Vitnam War. His experiences there led him to publish the book Tulsa in 1971. It was a landmark work: a photo documentary illustrating his young friends' drug use in black and white. His follow-up was Teenage Lust (1983), an "autobiography" of his teen past through the images of others. It included his family photos, more teenage drug use, graphic pictures of teenage sexual activity, and young male hustlers in Times Square, New York City. Clark constructed a photographic essay titled "The Perfect Childhood" that examined the effect of media in youth culture.His photographs are part of public collections at several prestigious art museums including the Whitney Museum of American Art, and the Museum of Fines Arts, Boston