Looking for something not too early or too long? How about 10 miles of mostly singletrack goodness in the southern part of Redwood Regional Park? Though I would't call it easy for most, it's not epic either. You can actually have the afternoon for other things if you want ;)
Highlights: A 10-mile loop of luscious terrain, mostly soft dirt surfaces (okay, a few roots here and there, and maybe a bit of mud depending on recent rainfall). Some nice vistas, tall redwoods, oaks and bay trees.
Req'd: Experience with running 10 miles on hilly trails and ability to read trail maps, plenty of positive attitude, and calories/water if you'll need them. There is a drinking fountain about halfway through (see map). About 1500' of gain.
Route: Printout and bring this PDF (suggest color print): http://files.meetup.com/948670/Redwood%20Reg%2010%20Mi.pdf
Meet in parking lot (see link above).
Optional lunch at nearby Cambodian restauruant in the Laurel District, Phnom Penh, 3912 MacArthur Blvd. Yum. http://www.phnompenhhouse.com/hours-and-locations.html