I thought I'd say something about Pacific Coast Trail runs because they hold fantastic trail runs throughout the west coast (mostly california, and mostly bay area). Trail running is an experience in its own, as much as mountain biking differs from road riding. These events are non-competitive, well planned out, beautiful scenic routes, well stocked with food/candy/water/sport drink. For almost every event they have 10k, 20k, 30k, and 50k option. These events are great for the first timer, to the ulthra marathon runner. Their website is very informative, check out www.pctrailruns.com