Yosemite National Park and USGS scientists, in collaboration with academic geologists, recently completed a comprehensive study of rockfall hazard and risk in Yosemite Valley. This internationally peer-reviewed study utilized new data and technologies to map the cliffs and talus slopes, date ancient rockfalls, and perform computer simulations of potential future rockfalls. This information was used to identify a rockfall hazard line on the valley floor. Existing structures within this line were evaluated using a numerical “risk metric” that quantifies the risk posed to human life and safety. This study represents the first time that rockfall risk has been quantitatively assessed in Yosemite Valley. https://www.nps.gov/yose/learn/news/rockfallrisk2012.htm