20-year-old Grace Rohloff was hiking the Half Dome Mountain at Yosemite with her father Jonathan. The weather forecast had said there would be clear that day, but as they approached the peak, it started to rain.

So they started to descend the mountain, but it's very steep and became slippery because of the rain. Grace slipped off and fell to her death.

https://www.sfgate.com/california-parks/article/college-student-death-half-dome-yosemite-19591633.php