She died on Monday at a New York hospital after a long battle with a blood illness caused by bone marrow failure, her close friend Kelly Cutrone said.
Mark's subjects ranged from runaway children and heroin addicts to celebrities and world leaders. She also pointed her lens at members of the Ku Klux Klan, a women's security ward in a mental institution and various celebrities.
Over the decades, "what resulted was, in fact, a lamentation: one of the most delicately shaded studies of vulnerability ever set on film," wrote the late Time magazine art critic Robert Hughes.
The photographer chose Seattle "because it is known as 'America's most livable city,'" she wrote in the preface to her book on the subject. "By choosing America's ideal city we were making the point: 'If street kids exist in a city like Seattle then they can be found everywhere in America, and we are therefore facing a major social problem of runaways in this country.'"
Her latest project, for CNN, was New Orleans on the 10th anniversary of Hurricane Katrina.
Mark was raised in Elkins Park, Pennsylvania, just outside Philadelphia. In 1962, she graduated from the University of Pennsylvania with a bachelor of fine arts in art history and painting, followed by a master's in photojournalism.
Her work drew attention in the 1960s, when she photographed heroin addicts in London, steeping herself in the humanity of overlooked subjects.
"She was a snake charmer of the soul," said Cutrone, an author and publicist who considered Mark "like my divine mother and mentor." ''She had the ability and intuition to see inside people, to evoke their soul."
