Thinking of going for a hike? There's no reason to leave the city. Just head up to Mt. Sutro and take a glorious walk along the historic trails that have been resurrected and lovingly maintained by the heroic Mt. Sutro Stewards. Why heroic? Because in order to keep the trails usable they have to rip out invasive parasitic plants on slopes so steep they're practically vertical. By doing so they've uncovered an amazing trail network that goes back 100 years, and restored the native plants to the hillsides. There's a lovely native plant garden at the tippy-top where a military installation once stood.
Also, on SFGate.com (1/2/10): http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2010/01/02/CMB21AM4MN.DTL