We see these in the yard on a regular basis throughout the summer. My first instinct is, well, clearly that's a 12-spotted something or other. But since dragonflies tend to be named for the flashy males, distinctive females like this one end up with nonsensical names. This is the female of the common whitetail Libellula lydia*, named for the male's frosty blue-white abdomen. Like the meadowhawks discussed earlier, this species wanders from from the water (where they spend their larval days) to hunt in fields and forest edges, and the suburbs that approximate such habitats.

* This name is not accepted by all (notably bugguide) but seems to rule the day on wikipedia at least. "Libellula" is coined in scientific Latin from libella, which itself refers to a very small coin. What the hell does that have to do with anything? Beats me, but was more than I could find out than I could about "lydia," which seems to always have been a woman's name, derived from the name of an ancient land in present-day Turkey.