Joshua Tree National Park, located in the Mojave Desert, is over 2.5 hours away from LA, so it's not exactly in the Los Angeles area, but plenty of people from the city still unsurprisingly make the trip on a regular basis. Not only is this National Park a world-class climbing destination, featuring hard granite and lots of routes, but it's also a really great place to spend a weekend backpacking and camping.
What Makes It Great
There are several campgrounds spread throughout the park. "Hidden Valley" campground is perhaps the most popular for climbers, as it's surrounded by plenty of routes only steps away from your tent. Backcountry camping is allowed, but permits must be attained at the Park's Headquarters. Be aware that summer months can often be unbearably hot, so maybe consider a fall, spring, or winter camping trip.
Now let's get to the good stuff... the climbing opportunities at Joshua Tree! There are literally thousands of routes, which make this destination a central hub for climbers from all over the world. The rock here features slabs, faces, cracks, and mixed climbing routes of all shapes and sizes. There are endless amounts of traditional style climbing opportunities. The sport routes are generally classically bolted, which means there are a minimum amount of bolts for protection of the rock, but this is one of the special characteristics of J-Tree.
And the bouldering options go on forever, and it's quite feasible that you could spend multiple lifetimes trying to attempt them all. There are some 2 to 3 pitch routes, but most fall around the 1 pitch spectrum. One thing to keep in mind is that Joshua Tree is known for being under-graded for travelers from afar, primarily due to the classic style routes and hard-to-climb granite.