A long time ago, in 1996, something really big and kind of scary happened in Yosemite Valley. There was a big hill, or cliff, called Glacier Point that started to move and crumble. It was like a giant puzzle piece was coming apart and sliding down the hill.
A lot of rocks and dirt started falling really quickly, kind of like when you pour sand out of a bucket really fast. The falling rocks and dirt caused a lot of damage to the area around the hill, like a big game of dominos. Trees got knocked over, rocks blocked off roads, and parts of buildings got destroyed.
People who were in the area had to be very careful and move to safer places, because the landslide was really powerful and could hurt or crush them. It was kind of like a really, really big earthquake.
Eventually, the landslide stopped and people started to clean up the mess it made. They had to fix roads, remove big boulders, and make sure people were safe. It took a long time, but eventually everything got back to normal.
Now, people who visit Yosemite Valley can still see the big cliff where the landslide happened, but they also know that nature is really powerful and can sometimes be a little scary too.