They found the final body from the Keyhole team today. The combined loss of life in Hillsdale and Zion is supposedly the largest of any natural weather event in Utah history. its bigger than the infamous flood in Antelope canyon almost 20 years ago.
Third, it is important to remember that the return intervals (or better put the odds of an event in any given year) are for a point. Monsoon convection is highly localized. Precipitation rates like those above might be rare at any given location, but they are quite likely to happen somewhere in southern Utah in any given monsoon season. For this reason, I don't consider the Hildale precipitation intensities to be all that unusual, even if they led to an unusual flood by recent human experience in the Hildale area.
Compelling reason to understand Utah weather and our decision making. I presented at a conference a decade ago about the broader lessons to the outdoor community from the "heuristics" analysis in avalanche studies. More and more we see evidence that the "human dynamics" are undervalued and under analyzed in the field. The short lesson is be aware of how and why we make decisions in the field as they have direct affects on risk and outcomes. Not sure there is a more specific lesson from the Zion deaths other than that and know what monsoonal storms can mean for the region.
Be safe out there as we have another couple weeks of the monsoon.