Braided fluvial tufa system in upper Las Vegas Wash

A "carbonate river frozen in time." In the upper Las Vegas Wash, a braided fluvial tufa system that is unique in North America preserves rivers and streams that last flowed more than 12,000 years ago. This tufa system is just one of many of the geological wonders that make up the new national monument. (Photograph courtesy of Craig Manker.)