Terrific rockfall resource

The Colorado Geological Survey publishes a terrific quarterly newsletter on "all aspects of geology throughout the state of Colorado. The latest edition, which is available online for free from here, focuses on rockfalls. It is a terrific read, with some very interesting articles on how and why rockfalls happen; how they can be detected; mitigation approaches; and a number of case studies. It is illustrated with some great photos as well. My favourite two, showing the range of scales of hazardous rockfalls:


And this "spot the difference" is rather nice too. The images were taken about 120 years apart: