>> reporter: toni's friends at work couldn't believe it either. >> i got a call from christy at our office and all she said is, tammi, toni fell >> reporter: what did you think when she said she fell >> i just said, is she okay? no, she died and i fell to my knees and my husband said, oh, my gosh, what's going on? and i said, dr. henthorn fell off a cliff. >> reporter: everyone was heartbroken for toni harold and, most of all, the henthorns' 7-year-old daughter haley. >> i put myself on the mountain and at the moment that she probably knew, well, this is it, you know i know her thoughts were of haley. >> reporter: about 150 people die in national parks each year. in rocky mountain national park, the leading cause of death is falling. >> before i wrote this book, i didn't know that the national park had investigators