From the Westridge Trailhead, go up the fire road a little way before turning on a narrow trail and dropping into Sullivan Canyon. Take it slow on this descent, because the surface is unstable in places. This slight up and steep down is the introduction to the run, and next comes the long but gradual ascent of the canyon. It’s an even-surfaced dirt path under shady deciduous trees, following a small creek that flows seasonally.
After about 3.5 miles of this gentle climb, the track turns sharply uphill and makes a few switchbacks in a side canyon to meet with Sullivan Fire Road on the ridgeline. There you have the option of taking the road or the singletrack undulating beside it, which is favored by mountain bikers. Both options lead to the same place–an even higher dirt road, which is the unpaved extension of Mulholland Drive.
There, you’ll get a view off the other side of the big ridge, toward Encino Reservoir and the San Gabriel Mountains beyond. Mulholland stays mostly level as it traces the ridgeline to San Vicente Mountain Park. This small summit park is often crowded because it’s accessible by car, but if you haven’t been, it’s worth a stop to see the historic missile site and to climb the radar tower.
From there, it’s downhill on the Mandeville/Westridge Fire Road, where you again have the option of taking the wide road or the tougher but more scenic mountain bike trail. All along this descent, you’ll look straight down the ridgeline at Santa Monica and the ocean. It puts you right back at the trailhead where you started, to complete a full-value run in the Santa Monica Mountains.