Mount Diablo is a mountain in Contra Costa County in the San Francisco Bay Area (3,849 feet). It is where the goddess Athena trapped Enceladus a millennia ago after the first Gigantomachy.

The Heroes of Olympus

The Lost Hero

Gaea freed Enceladus from Mount Diablo, and Enceladus uses the mountain to imprison his enemies like Tristan McLean. Jason Grace, Leo Valdez, Piper McLean, and Coach Hedge went to Mount Diablo to free Piper's dad. Jason killed Enceladus with the help of his father Zeus Piper and Leo and re-trapped him in the mountain.


  • The Native Americans of the area, Chumash, lost a battle against the Spaniards there earning the mountain its name, the Devil Mountain (in Spanish). It is considered a cursed yet holy place for them.
Locations (CHB)
Magical Locations: Olympus | Camp Half-Blood | Camp Jupiter | Aeolia | C.C.'s Spa and Resort | Daedalus' Workshop | Lotus Hotel and Casino | Mount Othrys | Ogygia | Pan's Cave | Sea of Monsters | The Labyrinth | Tartarus
Cities, States, and Towns: Alaska | Bar Harbor | Chicago | Detroit | Gila Claw | Jamestown | Long Island | Manhattan | New York City | Quebec | San Francisco | Vancouver | Westport
Other Locations: Apennine Mountains | Aunty Em's Gnome Emporium | Crusty's Water Bed Palace | Empire State Building | Gateway Arch | Grand Canyon | Greece | Hoover Dam | Junkyard of the Gods | Mount Saint Helens | Polyphemus' Island | ROFL | Rome | Triple G Ranch | Waterland | Mount Etna | Mount Diablo | Mount Tamalpais | Pikes Peak