Posted by The San Francisco Dog Walker
Nope! This is not paint or fire retardant!
The orange-rust color is an algae which has been observable at Sutro Height Park near Land’s End over the last several years, but park officials and foresters are not concerned that it poses a health safety risk.
The rust-dark orange algae,Trentepohlia aurea v. polycarpa, can now be found along the seawall from The Cliff House all the way down the sea wall of Ocean Beach.
This algae thrives on ocean salt spray and forms dense colonies on Monterey Cypress trees along the Pacific coast.