When Spanish explorers first mapped San Francisco, what they found would surprise today's residents. Nearly every valley had its own arroyo, or a creek that only appears when there's enough rain to fill it. A new art project will place them under the feet of busy commuters, approximating in paint or light where the small waterways used to run.

The concept was developed for the Market Street Prototyping Festival by designer Emily Schlickman and her collaborator, radio producer Kristina Loring, who will contribute a soundscape for the project.

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Though they're hidden, some of the creeks still exist in a way. They've been routed underground and tied into the city's sewer system.

The Oakland Museum of California has created a map of the hidden waterways and reports that in Hayes Valley, where Hayes Creek would have run in wet weather: "It is said that a high groundwater table can be found at the basement of the San Francisco Symphony Hall and other Civic Center buildings."