Any advice on some good hikes in these areas? Also, I was wanting to get some bouldering in while at Joshua Tree. Any advice on a good area? or a campsite next to some good bouldering? I'm only starting to get back into rock climbing after a break so Ive only been doing V1 stuff, V2 at the most. So nothing too gnarley.
In JT there are peak hikes, some with trails like Ryan Mtn. I liked Queen and Quail if soloing is your dish. You may run into some people, though, the L.A. HPS is big on peaks. I sure liked the free camping at Jumbo Rocks (2002 or so)! Fine eats in the towns to the north.
You do have to watch it in Mojave NP, there's very little rangers about, so you can get into big trouble. No trails or signs to say which way to go. Teutonia Peak was a nice class 3-4 scramble to the top, there's an official trail to about there. You ought to be O.K. on Clark Mtn., finding the right route (cl. 3) is critical, though. I know the way on most all else, but since I am an aging peaker, and that I've done many such peaks a couple times, I refrain from repeats unless I can take a partner. Kelso Dunes is safe enough.
In DV there's Panamint and Eureka Dunes, I solo'ed Eagle Mountain (3,806'), class 3, and DV Buttes was good for a couple hours. I also solo'ed Coffin Peak, a safe enough hour hike, and if somehow Telescope was safe enough, you might see others to lend a hand should some freak emergency come about.
There's plenty more peaks everywhere, but as I do not solo many of them, I advise the same. Pretty much no one will come to get you. You can try asking the rangers to check it out when you do not report back, if agreed previously, but the desert nights are cold. No water sources to sustain you. I've had some close calls, so be careful.