The CABY region consists of four watersheds (Cosumnes, American, Bear, and Yuba) and 12 subwatersheds situated within the north central Sierra Nevada in California.
The IRWM area extends from the northern parts of the Yuba River watershed in Yuba, Nevada, and Sierra Counties to the southern part of the Cosumnes River watershed in Amador County. The CABY region land area comprises 4,351 square miles, or about 30 percent of the Mountain Counties Area as defined in the State of California Department of Water Resources (DWR) Water Plan Update (DWR 2009). All four watersheds include headwaters that drain large volumes of water into the Sacramento and Mokelumne Rivers, ultimately serving the Sacramento Delta ecosystems. The CABY region encompasses only 2.4 percent of California’s total land base and is home to a small fraction of California’s population, but its significance both ecologically and economically cannot be measured by its size or number of residents.
The American, Bear, and Yuba Rivers provide 24 percent of the total Sacramento River flow as measured at Freeport. The Cosumnes River, southernmost watershed in the CABY region, provides flows into the Mokelumne River that then drains directly into the San Francisco Bay-Delta. Combined, these watersheds produce water supplies for the Greater Sacramento Region – a population center of over one million people – and greatly contribute to water flowing through the Bay-Delta, helping with environmental needs, salinity concerns, and water quality issues.
The CABY region also provides significant economic resources to the entire state, serving as the source headwaters and contributing a significant portion to California’s water supply, including flows for the Bay-Delta system, the Central Valley Project, and the State Water Project. Moreover, the CABY watersheds generate thousands of megawatts of hydroelectric energy serving communities far beyond the region through California’s electrical grid system.