Thanks for your insect question. I'm afraid I can't see the individuals clearly enough to identify them (but they are not bees), so will assume they are yellow jacket wasps. (You might use the photos in this link to identify them.)
Here's another link to an OSU Extension article about yellow jackets. As you can read, "By fall, yellow jacket nests have produced a crop of new queens and males. By the first frost, most workers and queens leave the nest to find a protected spot to spend the winter. They emerge in spring to begin the cycle again. Only new queens survive the winter, however, and they almost never reuse the previous year's nest." I'm assuming this is why you found so many of them in one place.
Why they all died at the same time and in the same place would suggest either that they were 'treated' to an insecticide or that they are the males which, having mated, died off, as described in this article. It does seem a bit premature for them to be dying due to the temperature, but, depending on where you are in Multnomah County, it has gotten as low as 46 degrees (9/22/17).
In answer to your question, there really is no one to notify, and you are at no risk. You might want to keep track of other similar events, though, to see if you can establish a pattern. Since the forecast is to be warmer this week, night time temperatures should be warmer as well, and this 'trend' may be averted until later in the fall.
Hope this is helpful!
Thank you for your response. I'm including another photo, closer than the last. These are not yellow jackets. From what I found, it looks like bald faced hornets. So my question is, does the information about yellow jackets hold true for hornets? There was no one around our home that used a spray, so if they had been sprayed, how far could they fly until they die?
Thanks. Yes; with a closeup photo, you can see the distinctive yellow and black lines on the abdomen. Interestingly, they, too are a species in the yellow jacket wasp family. So, the information I previously linked you to is the same for this type of wasp. But, here's another link to information about this species. Were they sprayed with an insecticide, death would occur almost instantaneously.
I really think this is just the onset of fall cooling, and the inevitable progression into their next life stage.