If you are interested in the wide variety of plants found in Joshua Tree National Park, then a hike to Pine City is a must-do. I consider this to be the park's best kept secret when it comes to hikes, and anyone will appreciate this moderate stroll to a very cool rock canyon.
The trailhead for Pine City also serves as the start to the short hike to Desert Queen Mine, which is a nice addition if you have some time. From the parking lot, head north on the well established path (1). The trail parallels a large wash on it's eastern side which breaks away just before you reach the Pine City site about 1.5 miles into the hike. This is a very mellow hike; the distance is short, the path is good, and there is very little elevation gain. Take your time moving through here and really look around at the fantastic flora that surrounds this trail. I think this is one of the best places to see the full range of plant species in the park. Along the way you'll see joshua trees (2), yucca, barrel cactus, silver cholla (3), pinyon pine, creosote, and juniper (just to name a few).
You'll know Pine City when you see it. A small rise overlooks the maze of rocks and dense vegetation below. The trail forks and it's up to you to explore at this point. Traces of human impact from the past can be found in the form of a small well and scattered log cabins, but this area is largely nature that is fully intact. Explore this rock labyrinth (4) and pay attention to how water loving plants thrive in this region (5) protected by the shady rocks and fed by seasonal rains.
You can continue north for another 0.5 miles to a really nice overlook of Twentynine Palms to the north. Though this is a relatively short hike, you can easily spend an entire day here exploring and resting in the shade. When you are done, head back the way you came in (6).