This image is the most popular of the Moss in the City photos. You are seeing a small metal cover 5-6 inches across on a driveway on Masonic at Brighton in Albany, CA.
This photo reminds me of the abstract paintings of Catalan artist Antoni Tàpies. I lived in Barcelona, Spain when I was 20 (1985) and Tàpies’s work was very popular. He creates elegant, enthralling compositions inspired by graffiti and the city.