Thanks for the help, flytyer.
I went back tonight and the spinner fall was nearly as spectacular as the previous night. I collected some of the spinners for observation and they indeed have a rust brown body, long tails, and seem to be about a size 10. However, something new I did notice this time is that although the spinner wings are mostly clear, there are some blotchy, mottled, dark markings on the wings. In fact this ordered, mottled pattern looks a lot like pictures I 've seen of the spinner wings of the Brown Drake. Do both the Brown Drake and Isonychia have wings that have such markings, rather than having a completely clear wing?