Tecolote Canyon Natural Park is located in San Diego just east of I-5, relatively near Mission Bay and Sea World. According to their website (linked above) the park has 6.5 miles of trails, however this number seems low as a full out and back of the entire park will clock about 17 miles, with approximately 12 under your belt by the time you reach the far end and return by the most direct route. Except for the two road crossings linking the South, central and Northern sections of the park, it's easy to forget you're in the middle of the big city. Most areas have little or no traffic noise. There is a ton of shade throughout the park so this one is a must on a hot day.
Suggested route: Park at the far east end of Tecolote Rd. at the nature center, grab a paper map and say hi to the rangers.
*Warning: although a guidebook and other resources say it is kosher to use the shortcut past the northern end of the golfcourse to link the southern and central section, the numerous "no bikes/no hikers/private property" signs beg to differ. I do not suggest testing the issue. This trail system is too sweet to risk losing.
Main trailhead: From I-5, exit at Tecolote Rd./Sea World drive. Head east on Tecolote Rd. until it dead-ends in the parking lot for the trailhead.
Northern trailhead: From 805, exit Clairemont Mesa Blvd, heading west. Turn South on Genesee, and West on Bannock Ave. Park at North Clairemont Community Park, and locate the trailhead at the far southern end of the paved bike loop in the park.