Twin Sisters is the twin-peaked highest summit in Northern California’s Howell Mountains, standing on the ridge between Suisun Valley and Napa Valley and serving as a prominent regional landmark. Its north and south summits give it a distinctive identity, and the name was already in use by 1879. The south summit is associated with a fatal Army Air Corps bomber crash on October 24, 1941, in which all five crew members died, with some wreckage still remaining. In the twenty-first century, the south summit drew attention as a privately owned peak where a large house near the crash site prompted debate over ridge-top development before it was destroyed in the 2017 Atlas Fire.