Carmel Mountain Preserve

Carmel Mountain Preserve in San Diego has an extensive trial system, you can end up hiking 7 or 8 miles on the official trails, and there are quite a few more unofficial trails. The preserve has no facilities, and a little shade. Hiking is mostly on sandstone or dirt / sand trails. There are some keep out areas due to the vernal pool's ghost shrimp in the winter and spring. There are some moderately rugged areas, or you can stick the more dirt road like paths. The place is not busy, there are several small, free parking lots and available street parking. Hiking San Diego County has an additional write up.

A horse path under Carmel Country road.

North Fortuna, Mission Trails Hike

North Fortuna in Mission Trails Regional Park is part of the 5-Peak Challenge and getting there is probably the most interesting hike of the five peaks.  At least in the winter or early spring, once it dries out it is probably not as interesting. There are several routes, I found the lower part to the Oak Canyon trail not obvious with many chances to get lost, so maybe take a map.  The trails at the top part are obvious. If you take the Fortuna Saddle route, there is a really steep climb at the top, so you have a couple miles of relatively easy trail then BAM, a half mile of steep uphill.  The round trip is 5+ miles depending on the route, but not really something you could kick out after work.

Torrey Pines Extension

Torrey Pines Extension has one advantage over Torrey Pines (non-extension), free parking.  Also low crowds, you'll only see a few people instead of a few dozen.  Plenty of space to hike around here, you can stretch a hike into 5 or so miles if you investigate all the nooks and crannies. There are multiple entrances with small parking lots or available street parking. Some shade (you know from Torrey Pines) no facilities.  See Hiking San Diego County for a complete write up. Below is a trail map I picked up at the site, I parked at Mira Montana Drive, I think the Red Ridge Trail may be the best part.

Torrey Pines State Beach

Nice place for a sunset walk.

Crest Canyon Del Mar, California Hike

Crest Canyon is smack in the middle of Del Mar, far enough from the coast you can't really see the ocean, there are a couple places to park on Durango Drive or right on Del Mar Heights is the very start.  It is all street parking with no lot, but it doesn't seem like it would ever get crowded enough to be an issue.  Try 2250 Del Mar Heights Rd, San Diego, CA 92130 for directions.

It is mostly desert scrub with a good view of the surrounding neighborhoods at times.  It is a good place to bring kids as the hike is short and just adventurous enough to keep them interested.

It was a struggle, but I managed to get to 2.5 miles round trip, the north end of the hike was fenced off with temporary fencing, so I assume it will open up in the next few months. But you could not link up with the river park.  Hiking San Diego County has a write up.