The danger presented by cliffs is obvious. Be extremely careful and watch small children around cliff edges. Falls from 3000 feet will kill you. Do not swim in pools above waterfalls. This again may seem obvious but every year people die by being swept over waterfalls in Yosemite. Do not climb on boulders below waterfalls. Wet boulders are extremely slippery. Also always stay on established trails. As employees, we constantly heard stories of someone who wandered off trail and had rocks crumble beneath their feet causing them to fall, sometimes just several feet but more often several hundred feet.
I didn't realize I was afraid of height until I visited Yosemite. If you are into hiking like me, watch out for slippery spots. Given the dramatic elevation change in the Park, any slip can be life-threatening.
The attached photo was taken from the top of Yosemite Falls. The bird's-eye view was brilliant. Just don't fall off the edge or you will travel 2,425 feet in the air and return to the Valley in seconds.
While visiting the rivers and waterfalls, do NOT scramble about on top of the rocks. They are slippery, often unstable, and very treacherous. Far too many people have been injured, and sometimes killed, due to carelessness of this kind. Rather than become a candidate for a Darwin Award, just stay on the trails. Heed the signs!
This lovely little sign warns of the dangers at the top of Ilillouette Falls. We filled our water bottles here, but had to be extra careful. The wet part of the rock was like glass and if we had put our weight on it, down we would have went. It would be like a giant natural waterslide with no traction whatsover.
Yosemite is surprisingly touristy and surprisingly untouristy. As in, I was surprised by the number of people that go, and how crowded the valley floor is, but I was also surprised that, for a place with so many tourists, the park had nondescript trailmaps, few rangers around and a general sense of danger. When we got back to camp, we learned that someone died while climbing up half dome right before our friends got there. But then again, I find that people who are used to the outdoors have no idea how clueless to this stuff city kids are. City kids know about other things, but there's just no need to learn how to wear mud boots, how to put on snow chains or that poison oak even exists. Especially in paternalistic San Francisco, where the solution to suicide is a fence. I guess what I'm getting at is that there are few fences in Yosemite.
Spring and Summer rivers are overflowing from melted snow. Stay away from rivers during high waters. No rock hopping since rocks can get slippery.
Always be careful crossing natural bridges.