The Los Pinetos trail connects the Angeles National Forest to the Placerita Nature Center park. It is a very tough climb from the Placerita Nature Center so most climb the Santa Clara Truck Route from the South end of Newhall Avenue and then come down the mountain via the Los Pinetos trail.
The trail is very steep, loose, and rutted at the bottom. But near the top the trail is shaded by oak trees and very pleasant to ride ... up or down. It's a bitch to climb, but great fun to descend. 100% singletrack.
Los Pinetos is very popular with hikers and equestrians. So be very careful coming down. There are countless blind corners. It's not uncommon to find a hiker coming up around a corner when you're on your way down.