The So Cal mountains area good options, albeit it takes a concerted effort to leave the crowds behind, and such areas are not large land tracts. You will find minimal human presence, however, if you commit to the effort required to leave the day hikers and PCT hikers behind. The good news about the drought is it has discouraged camping in areas that previously had water resources, but now are dry hikes. The bad news is they
are dry hikes. The ones listed below all have water if you know where to look; understanding the regional hydrology and a geology map indicating local stratigraphy is a great help in that endeavor. For example: the maps indicate numerous water sources originating at the 4600 - 4800' elevation all along the south facing slopes of the front range of the San Gabriel Mountains. But in a sustained drought many of these once dependable year round water sources have been reduced to seasonal flows, due to less annual precipitation. This season may break the trend, due a superlative, wet season.
- Wiki "East Fork San Dimas Canyon", or "San Dimas Experiment Forest" or Glendora Ridge Road Experimental Forest". They are the same place with variations on the name. This area is all below 6K' elevation, and faces south onto metro So Cal. On clear days the Channel Islands are visible, and at night the city lights are spectacular! There are some trails, and some water (if you know how to find it). The main appeal is in the upper part of the canyon; it gets very few visitors and is mostly XC bushwhacking. If you like coastal scrub ecology, this as a gem. Black flies and ticks may be a seasonal nemesis.
- The San Gabriel Wilderness has very few trails, and very rugged XC terrain. The wilderness area was designated as part of a program to re-establish the black bear in the region. The wilderness covers the area west of Hwy 39, east of Short Cut Picnic Grounds, north of the West Fork San Gabriel River, with the wilderness area's the northern boundary straddling Hwy 2. It has a jagged, meandering boundary and excludes certain lands located within its interior (e.g. Crystal Lake), all to accommodate previous development. The wilderness parkland itself has very little trail access, which makes moving around in this extremely rugged terrain very challenging. Black flies and ticks may be a seasonal problem.
- The Idyllwild side of Mt San Jacinto. This side of the mountain receives a mere fraction of the total visitors to the mountain. With exception given to the Humbler Park trailhead, the other trailhead heads of the area receive light traffic. Most of the hiking done in this region is along the PCT.
There are a several web sites focusing on So Cal back country activities, in addition to official gov web pages, for example
http://perryscanlon.com/ focuses on the San Jacinto area, while
https://www.simpsoncity.com/hiking/y has mostly San Gabriel Mountain content. Similar sites exist for the San Bernardino Forest and other parklands of So Cal.
Ed"
edit: "Hwy 36" corrected to "Hwy 39"and other minor changes
I like soloing with friends.