Dirt Mulholland is a good beginner trail. Not very scenic, but you do see the Valley below and all it's splendor. Super easy fireroad riding. No major climbs, just gentle rolling ridge top riding. There are some loose gravel sections because the rangers pave some section with gravel for emergency vehicles.ybonics said:
The Betty Dearing trail in Studio City is easy if you stay on the main fireroads. More climbing on this trail, but the fireroads are easy to negotiate. Stay on the designated trails, many bikers have created their own single track here and it rubs the locals the wrong way.
Del Cerro in Palos Verdes is very scenic next to the ocean. Stick to the fireroads and it's an easy non technical ride. The entry from the trail head can be steep for some beginners, so just walk your bike down til you get the water tank. It's all easy on the way in because it's mostly descending. The way out is more exercise as it's a climb back to the trailhead.
A side note, many of these easy trails are also popular with dog walkers and hikers. A bell helps on these popular trails and keeps everyone happy.