Go east on Interstate 8 from the SD area, and go north from Exit 47. This is the Sunrise Highway into Mount Laguna Recreation Area of Cleveland National Forest. You'll soon be driving on scenic, winding mountain roads -- with all the thrills and dangers that go along with climbing to 6000 feet (2000 meters). This is NOT to be done during or after precipitation, as even light rain at the coast can become ice and sleet while going up these roads.
Make a stop at Mount Laguna Lodge & Store, getting the guide books and the day pass ($5 per car) you'll need to use the facilities along the road.
Then enjoy the views, the woods, the isolation (after a five minute walk), and the quiet. If the skies are clear -- and they usually are -- you'll get some great views. If there's recently been snow, you can have a snowball fight just a couple hours after leaving San Diego.