Portola Valley is located on the San Francisco Peninsula on the eastern slope of the Santa Cruz Mountains. The town is west of Interstate 280 and the southwest boundary is along Skyline Boulevard which more or less is the ridge of the mountains. The Windy Hill Open Space Preserve is a large part of the town's southwest side and the north side of the town borders Jasper Ridge Biological Preserve. Woodside borders it to the northwest and Palo Alto to the southeast The unincorporated subdivision of Ladera is adjacent to the northern boundary of the town. It is in a mostly wooded area, with some open fields. The San Andreas Fault bisects the town.