The drive is absolutely stunning, especially the view from Sierra Buttes. You'll have to get out for a little hike to reach the lookout, but it's worth it. You'll definitely want to bring extra water as well as your camera and binoculars.
Sierra City served as an important mining town starting in the 1850s. Today, the quaint town consists of many turn-of-the-century buildings complete with boardwalks. Don't miss the Kentucky Mine Stampmill and Museum east of town.