Seigler Mountain is a 3,692-foot volcanic peak in Lake County, California, within the Cobb Mountain area of the Mayacamas Mountains. Named for Thomas Seigler, who discovered nearby Seigler Springs, it became linked to a local resort that had developed there by the 1870s and to the broader history of settlement and travel in this part of the county. The mountain was active about 600,000 years ago, and lava from it and Mount Hannah spread across about 7 square miles. Seigler Mountain is divided from Mount Hannah by Salminas Basin, and a 2020 survey found it infested by Mediterranean oak borers.