Yep, It Happened in Marin County
The Point Reyes Light astounds with West Marin women strip for peace:

MAKING THEIR BODIES FIGURES OF SPEECH - West Marin women are serious enough about PEACE to spell it out. Wearing nothing but afternoon rain, 50 determined women lay down on Love Field near the Green Bridge Tuesday afternoon to literally embody PEACE and "show solidarity with the people of Iraq," said the organizers. "Women from all ages and walks of life took off their clothes, not because they are exhibitionists but because they felt it was imperative to do so," the organizers added. "They wanted to unveil the truth about the horrors of war, to commune in their nudity with the vulnerability of Iraqi innocents, and to shock a seemingly indifferent Bush Administration into paying attention."

Here's the photo. More details in the full story including a full plate of Marin wingnuttery:

Marshall resident Donna Sheehan, who organized the group called "Unreasonable Women" for the photo, said she’s been pondering for four years a way women can "be heard on a very deep level."
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Afterward, organizer Sheehan said the day had proved to be a beautiful and powerful experience for all involved. "I think it’s going to a make a mark in the political and art world," she said.

No clues were spotted anywhere in the vicinity.