Layered tuff, lapilli tuff, bedded agglomerate, tuff breccia, autobreccia, and lava, chiefly basaltic. Jurassic mafic volcanic rocks are present in the Stillwater Range in Churchill County, with smaller exposures in the West Humboldt Range. In the Stillwater Range they are intimately associated with gabbroic intrusive rocks (Jgb). They conformably overlie and locally are interbedded with quartz arenite (Jcg). The lavas are homogeneous basalts that contain microphenocrysts of labradorite, diopsidic augite, and talc-hematite after olivine. The groundmass is plagioclase-clinopyroxene-iron oxide (Willden and Speed, 1974). They are believed to be Middle Jurassic because they are thought to be comagmatic with the gabbro (Jgb). This unit is included within the 1978 State map unit Jgb.