I just learned that Boulder County has a "wear a mask" rule when exercising on trails. I tried to google the source of this guidance that when running outdoors, for a few seconds, that COVID infection is even possible. NOTHING. The only guidance I could find is this saying that it is NOT a good idea, so long as you can stay 1 m apart. What drives me crazy is these guys love to tout "science" when it reinforces their narrative, but when that's not the case it's just "our judgement"
CDC says "if unable to wear face covering, exercise outdoors in a rural area".