This is a good loop for locals. It's mostly easy with a few tougher climbs, stitching Deer Canyon Trail to horse trails to Ronald Reagan (formerly Toyon) Park. There is some pavement at the end to return to the Walnut Canyon Reservoir.
There's a trickle of water across the trail about two-thirds of the way down Deer Canyon Trail. It can be slippery - slow down before, go straight across, and don't brake while in the water.
Park on the dirt at Walnut Canyon Reservoir on East Canyon Rim Rd across from E. Nightingale Circle or at Canyon Rim Park. The Deer Canyon Trail trailhead is adjacent to the driveway at the corner of East Canyon Rim and The Highlands Rds.
Plunge down Deer Canyon, bombing down to the Canyon Mist Ln./East Hollow Road Entrance. Cross the road to the Four Corners Trail
. Climb (gently) through the ravine (between the backyards) to the corner of Sunset Ridge and Canyon Creek (to the right of the guardhouse). Cross Sunset Ridge to the horse trail on the other side.
Make a sharp right and then a quick left, which marks the beginning of a tough-ish climb towards a large water tank off to the left. Take a left at the top of the climb and head towards the water tank. Continue down the stairs. (Stairs are rideable for higher "intermediate" riders when trail is in good condition. [RIDE AT YOUR OWN RISK!] Watch out for sandbags and, if you do ride, aim for the shallower drops). Continue past the apartments parking on the horse trail, then take a sharp right up (usually well pine coned) hill to the Serrano Avenue crossing. This is a busy street with fast traffic - wait for a break.
As you cross, stay to the left of the horse trail, ride downhill, and then stay sharply to the right. There's a short, steep climb followed by a longer less steep climb. Stay on the main trail (there's a left that takes you over to Ronald Reagan [formerly Toyon] Park, skip it) and head towards the tunnel under Oak Canyon Drive. The tunnel is a little dark and creepy, but there are usually no obstacles in it. On the other side there's some singletrack up and down and one very steep climb up to a bridge. Continue until you come out on Blue Sky.
Take a right on Blue Sky, climb past Silver Star and go right on Night Star. Halfway down, take a left on East Marblehead which will take you back across Serrano. Turn left on Serrano up to Sunset Ridge, right on Sunset Ridge, and then left on The Highlands, which takes you back to the start for a total of just under six miles.
You can extend the ride with a circle around Walnut Canyon Reservoir (1.7 miles) or many other options in Deer Canyon, Ronald Reagan/Toyon Park, Weir Canyon, and Oak Canyon Nature Center.