Follow the trails to get a taste of what and have to offer for Mountain Bikers.
The Sycamore Canyon video is by Mountain-Bike-Diaries.com, a site that features videos of great trails from around the U.S. It was shot in December 2011 and more videos can be found at their Youtube page.
Mountain Bike Bill.com has a overview of the trail and how to find it.
The Mission Trails video was shot just days ago in the hills north of Santee. See more at the Youtube page. Mission Trails is listed as "Not to be missed" by the San Diego Mountain Biking Association, see their trail guide for the area.