About the site:
"The U.S. Geological Survey Denver Library maintains a collection of over 400,000 photographs taken during geologic studies of the United States and its territories from 1868 to the present.
These images provide a visual history of the discovery, development, and sciences of the United States and its Geological Survey. Some photographs have been used in USGS publications, but most have never been published.
Currently, this website represents less than 10 percent of the Library's images with approximately 30,000 photographs on-line."
Here are a couple examples of the photos hosted there. These were taken after the San Francisco Earthquake of 1906: