State Route 121 is a state highway located in the northern part of California. It runs approximately 25 miles, connecting the cities of Napa and Sonoma. The route primarily serves as a vital link for local traffic and provides access to various attractions in the region, including vineyards and parks. The highway features scenic views of the surrounding countryside and is often used by tourists exploring the Napa Valley wine region. State Route 121 intersects with several other major roads, facilitating travel to nearby areas and enhancing connectivity within Sonoma County.