There's also the Santa Monica Mountains national rec area. Wildwood park in Thousand Oaks (it is a bit on the smallish side but is cool for short day rides). ANY of the fire roads in the Los Padres National Forest. (Hint, the fire roads in north Santa Barbara county are longer than those in Ventura County and are more like the 3rd pic you posted.)

There are literally miles and miles of fire roads and single track trails out there to ride on.

One of these days I'm gonna get to Limestone canyon.