Silicon Valley is a place that sees many business travelers, some of whom want to combine their visit with some high quality hiking in the California wilderness. Most of these people know about Yosemite and Sequoia National Parks (four hours away), and some know about Big Sur and the Pacific coastline along the PCH (two hours away).
But sometimes these most famous of parks are not suitable. The drives are long, and some of the most famous areas require getting reservations ahead of time for camping, cabins or trails themselves (Half Dome). Also, in winter the higher elevations can be tricky for novice travelers. Are there any high quality hikes that are closer, or overlooked?
I would like this to be a canonical question to service all those business travelers who end up in places like Mountain View, Palo Alto, San Jose, Stanford (and many others) and who will probably try googling for their options.