Sarah - if you visit Northern Virginia again, you should check out Great Falls Park (Virginia side)---there are some great mountain bike trails there. Also, the C&O canal towpath runs from Georgetown to someplace in Maryland (miles from DC). Anyway, that one is a mix of gravel/rock/dirt and closer in to DC, it's a slight upgrade heading west. No discernable hills but believe me, if you head away from the city, you are slowly climbing. It's a beautiful ride, though, especially in the fall. It goes right along the Potomac River. I don't do dirt anymore, as I'm now strictly a "paved surface" rider now. My 42 year old bones don't like being jostled nowadays