California Hiking & Riding Trail
The California Hiking & Riding Trail is an unfinished plan for a 3,000 mile trail, extending from San Diego county near the Mexican Border, north through the Tehachapi Mountains and Sierra Nevada to the Oregon Border and returning southward through the Coast Range. The Trail has no dedicated Web site, but with a search on the Internet you’ll come up with a variety of sites that cover various sections of the Trail: http://www.sdctc.com/history.txt covers the Trail’s history and; http://www.sdctc.com/trailmap.pdf has an old 1950s map of the entire Trail, about the only one that appears to have been published.

Mission Trails
Centrally located and only eight miles northeast of downtown San Diego, Mission Trails Regional Park encompasses nearly 5,800 acres of both natural and recreational developed land. There are plans afoot to link the San Diego Sea to Sea Trail with the Mission Trails system via Sycamore Canyon, southeast of Poway.
http://www.mtrp.org/

Pacific Crest Trail
The PCT spans 2,650 miles from Mexico to Canada through three western states. It reveals the beauty of the desert, unfolds the glaciated expanses of the Sierra Nevada, and provides commanding vistas of volcanic peaks and glaciers in the Cascade Range. The Trail also passes through historic mining sites and evidence of man’s endless quest for natural resources. The San Diego Sea to Sea Trail crosses the PCT just east of Lake Cuyamaca.
http://www.pcta.org/

San Diego River Park
An organization dedicated to enhancing the San Diego River and working toward the establishment of a river-long park, from the headwaters in the mountains near Julian, California, to the Pacific Ocean in the community of Ocean Beach in the City of San Diego. The San Diego Sea to Sea Trail will connect with the Park near the headwaters of the San Diego River.
http://www.sandiegoriver.org./

San Dieguito River Park
is the agency responsible for creating a natural open space park - a 55-mile corridor - in the San Dieguito River Valley. The Park will someday extend from the ocean at Del Mar to Volcan Mountain, just north of Julian. Once both the San Diego Sea to Sea Trail and the SDRP trail systems are finished, they will link up 55 miles inland, forming a giant loop.
http://www.sdrp.org/

Trails.com
Wondering where else to go in San Diego to hike, bike, camp, paddle or even find a bit of snow? Apart from the San Diego Sea to Sea Trail? Which is mentioned, of course. Then try Trails.com, a great resource for high-quality outdoor travel content, and exclusive digital guidebook products in North America. You sign up, download adventures with the accompanying maps, and you’re off!
http://www.trails.com