What's the best day hike within an hour's drive of San Francisco?

Definitely the hike out to Bass Lake in Marin. drive to Bolinas (past Stinson beach) I can't remember the name of the road to take but if you look on bahiker.com you might be able to find it. You drive till the road is no longer paved, and end up in a parking lot. from there the hike is 3 miles over glorious cliffs overlooking the pacific and you end up at a hidden lake. On a warm day you can skinnydip in the lake and it's delicious. Stop at Walgreens on the drive over and buy an inflatable raft for 99 cents so you can lounge in the lake all day.

Alternately, you could drive to the ranger station at Mount Tam; that's less than an hour. From there there are a ton of amazing hikes with ocean view. There is one where you go thru the redwoods, down to the ocean, and can end at Stinson Beach. You can buy a map from the ranger for a dollar and s/he can recommend many great hikes.

tenessee valley in marin. also, anywhere in tilden park (berkeley.)

just to build on orli's note: you can also go past the lake on this hike and then come to a clearing with a brushy path that folows a creek and leads to a slow climb down to the pacific. once you are there, swing south and see a waterfall that drops 30 feet to the pacific. one could easily stay the night on the beach and would most likely see some seals and the like. very, very nice

There's a great hike that begins from the youth hostel in Point Reyes. It's about an 8 mile loop, goes through woods and then out on the cliffs looking over the coast and ends back at the hostel. It's really beautiful. The town of Point Reyes Station is also really lovely.

If you hike to Bass Lake, WEAR PANTS! There is lots of poison oak... itchy itchy itchy...

Most folks go north, but there's a great park that's part of the golden gate national recreation area outside of Daly City.