Years ago I burned up my clutch on Berdoo Canyon Road in my stock 1984 Toyota pickup! Joshua Tree also has a big area north of the park with many miles of dirt roads, the Dale Mining District. I had a flat tire on 3 of 4 trips there a few years ago. The Mojave National Preserve has many miles of dirt, including the Mojave Road, I’ve spent plenty of time there exploring old mines and such. The best National Park for exploring dirt roads though, is Death Valley. Lots of great trails. I haven’t come close to doing them all, but I have done the racetrack road to the Lippencott grade to Saline Valley, and Warm Springs Canyon to Mengel Pass, and out Goler Canyon. I did that one November when the Death Valley 49ers has a big gathering and watched a group of about 40 people on horseback coming up the opposite way. They were amazed that I was doing the trail in a stock Toyota, and I was amazed that they were doing it on horseback! I plan on doing Steele Pass sometime this winter.