Late Miocene to Pliocene sediments are widely exposed throughout northeastern Nevada. Exposures of Miocene (earliest Barstovian) to early Pliocene (Clarendonian) sediments occur along the northern flank of the Sheep Creek Range, the eastern and western flanks of the Shoshone Range, and the northern and western portions of the Toiyabe Range in Lander County, and the northern Reveille and southern Pancake Ranges in Nye County. Although not formally named, these tuffaceous sediments are very similar to the Humboldt Formation in Eureka and Elko Counties and typically consist of greenish-gray siltstone and clay, buff sandstone and conglomerate, and continuous white ash beds which are commonly less than 5 feet in thickness (Ekren and others, 1973; Stewart and McKee, 1977).

Miocene tuffaceous sediments in and along the northern Shoshone Range are about 800 feet thick. They consist of coarse pebble to cobble conglomerate with local lenses of coarse sandstone and coal, overlain by agglomerate and tuff. The uppermost units are channel conglomerates and sandstones that locally contain silicified logs, and black to dark gray siltstones that contain abundant plant debris (Gilluly and Gates, 1965).

Most of the Miocene sediments exposed in northeastern Nevada belong to the broadly exposed Humboldt Formation that is described separately below.