Tuffaceous sedimentary rocks, tuffs, pumicites, and silicic flows (Miocene) at surface, covers 1 % of this area. Moderately well indurated lacustrine and fluvial (flood-plain) deposits of tuff, pumicite, palagonite tuff, and lesser siltstone, arkosic sandstone, and pebble and cobble conglomerate. Locally contains some lignite beds.Web