How do you archive a performance? Can you put human speech and action under glass and frame it? Stow art that unfolds in three dimensions within acid-free archival boxes, to be filed away in a cool, dark vault?

The conundrum of how best to preserve the history of midcentury American performance art — art created before phones had video cameras — lies at the center of the Getty Research Institute's recently announced acquisition of Robert McElroy's archive. In more than 700 prints and 10,000 negatives, the photographer documented the performative works of Allan Kaprow, Jim Dine, Claes Oldenburg and other artists whose "Happenings" grew from niche New York art events into a full-fledged pop culture phenomenon.