Got anything specific in mind? There are all sorts being organised on this forum. Myself and another Brit (both in our twenties) are probably going climbing soon. Someone else is organising a 50ft Yacht excursion, there's bowling, and skating etc...
Next Saturday there are a few of us heading up to the MacRitche Reservoir for a wander....
Let me know if any of this interests you. If not there's always the WNDC (Wednesday Night Drinking Club) I've not been yet but heard its good fun and a good way of meeting new people.
Not that i know of sorry. I'd offer to show you around but i've only been here a week myself and have got to go out with my boss. First Friday here etc... Yawn...