Some of the specimens were collected from art patron (and SFMOMA board member) Steve Oliver's sculpture ranch in Sonoma. The landscape architects thought it would be auspicious to start with some lichen that was already "art-friendly." Soon after they collected the samples, they heard that a crew had spent years cleaning lichen off Mt. Rushmore—"Oh man, we missed that opportunity!" lamented Milliken.
Lichen is a pioneer organism that thrives where nothing else can—arctic tundra, hot deserts, rocky coasts and toxic slag heaps, for example. Lichen is intolerant of pollutants; in some European cities, they put lichen stones on rooftops and monitor its health to gauge air quality, mapping what they call "lichen islands."