Its been 11 day's and they should have some clues by now. Here's a map of the trail: Link , its a single path trail alongside the hill with little room to pass without stepping off the trail, and lots of Poison Oak. Trail leads directly to previous mining activity, and the area was within an earlier fire. Trail was closed early in 2019 for a good part of the year and maintenance being done. If poisoning was a cause, I'd guess maybe some old mine tailing's were disturbed containing high amounts of Cyanide. Its a really hot trail this time a year and requires a good supply of water. Being alongside the river with access in a few places, they might have drank some contaminated water.
