In a correspondence with Dennis Paulson, he indicated there are two variations of eight-spotted skimmers - an eastern and a western. The east/west delineation is the Cascade Mountains, though occasionally they will be found in the "wrong place". I have found both here in Elkton, west of the Cascades. Typically female Eight-spotted Skimmers lack white patches on their wings west of the Cascades and have them east of the Cascades. This image is of a typical western Eight-spotted Skimmer, female.
This is an eastern Eight-spotted Skimmer