El Mirage dry lake bed riding area is one of our favorite locations to ride. There are all kinds of riding environments to choose from. There is obviously the flat and hard dry lake bed that you can top out your bike on, but there are also hard-packed trails, sandy washes, open desert riding, and hills. There are also two tracks that you can use, one for kids and one for adults. Be warned though that the adult track is not well kept.
There are also two dozen or so large camping spots that have flat open areas, picnic tables, and even vault toilets. You can also camp anywhere you want in the area except for on the dry lake bed (you are able to camp on the perimeter of the lake bed).
Here is a video of my son who found a little track near our campground that kept him busy for hours.