There are so many awesome places to hike, it's hard to choose any one, or even a few. The places I go most though are:

Yosemite National Park- The Yosemite High Country to be specific. It's beautiful and you can escape the hordes of people who flock to Yosemite Valley.

Anywhere in the Redwood Forests on the Northern California coast.

Plus, I'm only minutes away from hundreds of miles of trails in the mountains that surround Silicon Valley.