That’s Paula Crist on the left. Crist toured as Zira in a Planet of the Apes show in the early ’70s and later became a stuntwoman, appearing in Battle of the Planet of the Apes and Logan’s Run, among others. She’s also closely associated with early Star Trek and sci-fi fandom, impressing Gene Roddenberry so much that he gave her a spot as a crew member in Star Trek: The Motion Picture. The event above is a convention called the American Quincentennial Celebration held at Grossmont College in San Diego County. See more at Flickr.
UPDATE (9/22/15): The young man on the right is William “Bill” Blake, who played Cornelius in “Meet Zira & Cornelius,” the “promotional roadshow,” as he calls it, mentioned above. Blake is a makeup artist (mentored by John Chambers, who won an Oscar for his makeup work on the original Planet of the Apes film), actor, and special effects technician. More background on Blake and his career can be found here.
Crist and Blake are actually doing professional promotion for Logan’s Run and thus “cosplay” is not exactly an accurate description. The title of this post has been revised accordingly.