This would be a very easy warm up for a runner. You would need to warm up again after driving further into the park to get to another trail.
For those entering Joshua Tree National Park from the south, the Bajada All-Access Nature Trail will be your first taste of the flora of the desert environment. The trail is actually several miles before the Cottonwood Spring
visitor station heading north. The run is a short 0.3 mi loop over a wide, clearly marked, hard dirt surface peppered with informational signage about each species of plant "on display." The parking area is ample for a run this size with both handicapped and large vehicle/RV spots. A Joshua Tree overview sign greets you at the trailhead which starts in the middle of the parking area.
A sign explaining what a bajada is starts you off before you cross a short but sturdy footbridge over a creek bed. You can see the entirety of the trail from the beginning so feel free to go in either direction and space yourself out from other visitors. The path winds around in a loop where you can stop and read signs describing each of the more common desert plant species you'll see many more times in the park. There are several benches to stop and sit and relax (not that you would need rest, as it's an extremely easy trail).
After reading the signs, you'll be an expert on ironwood, ocotillo, brittlebush, creosote, and mistletoe among many others! Seriously, later in the park you'll be able to answer somebody when they ask "what's this bush?" Except for Joshua trees; there are none in this area of the desert where this trail is located.
After your 20 minutes or so of meandering, return to your vehicle and get back on your way into the rest of Joshua Tree armed with just a little more plant expertise. While this is not a very fulfilling run, we definitely appreciated knowing a little more about what we were looking at throughout the rest of the park.
Brttilebush, creosote, ironwood, ocotillo, cactus, palo verde, chuparosa, indigo bush, mistletoe.