Mount Tamalpais

Mount Tamalpais is located on the outskirts of San Francisco and is the location of The Garden of the Hesperides.

History
It's the site where Mount Othrys was being rebuilt by the newly freed Titans as a war base during the Battle of Manhattan. Kronos, the Titan Lord of Time was assaulting Manhattan at the time so he could get to Mount Olympus which is on top of the Empire State Building. It is named the Mountain of Despair and happens to also be the sight where Atlas holds up the sky. Both ordinary Mist and magical Mist are very thick on the mountain. Many monsters are attracted to it. The mountain is close to where Annabeth's dad and his family live. Annabeth stayed there for the summer, saying she was able to keep watch on the monsters activity. It also isn't too far from Camp Jupiter.

The Titan's Curse


Percy, Thalia and Zoë Nightshade traveled here to save the goddess Artemis and, if need be, Annabeth, from Luke and the Titan Army's grasps. It is noted that the mountain smelled like eucalyptus, because dragons liked to chew it. Here, they fought Zoë Nightshade's father, the Titan General Atlas until they pinned him under the sky.

The Battle of the Labyrinth
Percy, Annabeth, Nico di Angelo, and Rachel Elizabeth Dare, a mortal, discover a passage in the Labyrinth that leads to Mount Orthys after going back into the Labyrinth hours after the fight against Kelli the empousai cheerleader, the spirit of Minos, and some dracanae in Daedalus' workshop.

The Last Olympian
Percy has a dream of the Titan gods Atlas, Hyperion and Krios talking, at Mount Tamalpasis, of the explosion of the Princess Andromeda, and of Nico spying on the Titans outside Mount Othrys.

The Lost Hero
Jason mentions that during the Second Olympian War, while the Greek Camp Half-Blood was in New York defending Mount Olympus and Manhattan against Kronos and his Titan Army ; during the Battle of Manhattan, the Roman demigods were fighting the Greek Titan Krios and the forces that remained there.