The most important thing you need to know about this trail is that it is heavily populated with hikers and dog walkers. Dogs are often off leash, and families with small children love this trail on the weekend. This is a great trail for catching speed, but watch the corners and use a bell if possible.
The southern trailhead - "Mandeville Canyon Entrance" - is located at the very end of a long residential neighborhood in the Brentwood/Santa Monica hills. There parking spots for a dozen cars, with plenty of parking spaces on streets just outside the gate. The neighbors with houses near the trailhead are surprisingly cool with cars cluttering up their street on the weekends, so pretty please be quiet and park your vehicle far from their driveways.
At the trailhead, you'll see a fire road trail and some signage on the left. On the right, you'll be able to see a narrow switchback - this is the start of the Westridge Singletrack
, which connects to the fire road several times. Ignore that for now, turn left, and start climbing up the fire road.
This gradual climb has a few minor downhill sections which give your legs a nice break. This road will take you all the way back to Mulholland Drive and the abandoned Nike Missile Control site. This is your turnaround point.
This is a great time to take a break and enjoy the views. They have restrooms, water and picnic tables. The trail is usually less crowded towards the northern end/top, but remember to keep an eye out for hikers on the way down.