I'm not an expert on dragonfly identification and am not totally sure about the identification of this one.   I'm fairly sure it's a female red rock skimmer, based on the fairly intricate abdominal pattern on a grayish background (and the species' distribution), but anyone who does know their dragonflies is more than welcome to correct me.   Red rock skimmers, as their name implies, tend to sit on rocks in streams, but this one was perched on some vegetation at the bank of a large pond at the San Jacinto Wildlife Area near Riverside, California.