I came across these unfortunate people in Peters Canyon. A rider was descending and collided into a female hiker. I don't know what lead up to the crash, but everybody was in good spirits. The female hiker complained of neck pain and was airlifted out of Peters by OCFA. The male rider suffered either a broken or dislocated collarbone.
If you ride in Peters, take extra precautions. Most hikers share the trail, but I've come across groups of hikers that will just not move even after I politely say, "Rider on your left."
I tend to stay away from Peters and ride in Santiago Oaks. It's a bigger park and way less hikers to deal with.