I hear ya' on the hills in Marin County! We just came back from riding there and it is very different than the riding I have done here in the East. Here it has been more short steep climbs, rolling terrain, roots and mud. I found that as long as the long steep climbs were not loose or technical I could generally find a rhythm and a gear to keep going. Throw in some switch backs or loose trail surface, and I found that I expended way more energy and had to stop more often. I have preferred the rolling, swoopy single tracks, but they usually require some climbing to get to them. I can see that riding hills will make you stronger quickly, though, so keep at it!

One place you may want to check out for some easier fun trails is China Camp in San Rafael. We did a nice 10-mile loop that had some climbing and switch-backs, but nothing that we had to get out of the middle ring for. There was enough to work on some handling skills, and lots of just fun riding.