Napa River marsh

Photo looking north at the Napa River marsh where USGS scientists collected sediment in 2019.

In October 2017, the Atlas and Nuns wildfires each burned over 20,000 hectares in the Napa River and Sonoma Creek watersheds in the north San Francisco Bay area of California. Contaminants in wildfire runoff can originate from anthropogenic activities, from geologic sources, or be created by fire itself, such as polycyclic aromatic hydrocarbons (PAHs). The USGS developed a linked terrestrial and marine sediment geochemical study in Napa River and Sonoma Creek watersheds and in receiving waters of San Francisco Bay to explore sources and dispersal of sediment and contaminants in runoff from the Atlas and Nuns wildfires, and their potential impacts on downstream ecosystems.