Nearly all the Marin Headlands is now part of GGNRA (Golden Gate National Recreational Area), but once it was the domain of the U.S. Army, and the region is dotted with former army posts and concrete fortifications. (The cannons themselves have been hauled away.) The gun sites started springing up as early as the Civil War. The Army kept beefing up its arsenal through the Spanish American War and World War II and finally added a couple of Cold War missile sites.