Last spring, the San Francisco Museum of Modern Art unveiled its new 14,000-square foot rooftop sculpture garden, spangled with works by Ellsworth Kelly, Louise Bourgeois and Kiki Smith. To a casual visitor, the space—with its wooden benches, dark stone walls, and cult Blue Bottle Coffee kiosk—looked minimalist but complete. It wasn't. Last week, CMG Landscape Architecture added their long-awaited finishing touch: a cultivated (and nearly microscopic) ‘lichen garden,’ possibly the world’s first. I joined them on a sunny Wednesday to help with the installation, and document the process.