There's a ton of great mountain biking around San Diego, but these five rides stand out for the scenery.
This is an out-and-back ride that follows the “The Impossible Railroad” through tunnels and over trusses along Carrizo Gorge. The railway was constructed from 1906 to 1932, and the history is amazing. Park at the gas station just off of Jacumba and the 8, then follow the dirt road signed “No Outlet” that heads back underneath the 8 (or drive the road and park at the De Anza Springs Resort). Catch the tracks just west of the road and enjoy… (Note that some of the spikes shown in the elevation profile are actually tunnels and should be flat. Also, there can be access issues - a train actually ran these tracks as late as 2011, and trespassers can be ticketed.)
Its not in San Diego but this one is too good to leave out. Ride one way from Two Harbors to Avalon, visiting Little Harbor, looking for buffalo, and enjoying endless ocean and rugged coastline views along the way. Though it can be skipped to shorten the day, the ridge loop around Avalon is highly recommended. Camp at Little Harbor to make a weekend out of it (camping gear is available for rent to avoid a heavy pack). Some red tape here - you must become a member of the Catalina Conservancy to get a bike permit, and bikes must stay on roads (trails are for hikers only). San Pedro is the only port that connects to Two Harbors – book early as dedicated bike slots fill up. The boat is free on your birthday…
A true classic. Ride one way from Anza to Borrego Springs via old roads, washes, and streambeds. You’ll have to deal with routefinding, bushwhacking, and stream crossings to earn that beer at the local bar’n’grill back in town. Note: the crux of the routefinding is figuring out how to get through Middle Willows - a brushy path is found on its east side.
This is a dirt-road ride that drops from Ranchita to the Tamarisk Grove campground in Anza Borrego State Park. Hard packed dirt leads through ranchland to patchy sand on the desert floor. Doable both ways for a workout.
A big climb or lengthy car shuttle (high clearance recommended) gets you near the forested summit of Toro Mtn (8716’). Fly downhill and back to the desert, passing through several vegetation changes as the air re-thickens. Santa Rosa’s summit is worth a visit on the way down (Toro’s summit is officially private property, though affords unmatchable views and the chance to see the leftovers of a helicopter wreck).