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The name Montini Volcano is applied to a much-dissected basaltic vent where Sinker Creek joins the canyon of the Snake River southwest of Boise Fig. (1). The name comes from Montini Ranch—now the Nahas Ranch—on the 1949 edition of the Sinker Butte Topographic Quadrangle (1:24,000). The Volcano is also partly with in the adjacent Wild Horse Butte Quadrangle. Downcutting by the Snake River and Sinker Creek has exposed the plug of the volcano and nearly 600 ft (180 m) of its surrounding tuff and lava.

The Montini Volcano can be reached from milepost 33 on Idaho 78 by following the road shown in Figure 1. Just before reaching Sinker Creek, a single-lane track negotiable by passenger cars leads down Sinker Creek to the central plug of the volcano Fig. (2). Although a gate has been installed at the head of the track to control livestock, the track is open to the public. From the plug, the track continues to a pumping station one mi (1.6 km) down the Snake River (NW¼Sec.6,T.3S.,R.l E.). From here, looking upstream, one has a splendid view of the dissected volcano (Fig. 3). Those wanting to see other parts of the Montin Volcano must back track to the Nahas Ranch and ask permission to use the ranch road. From the ranch headquarters, this roadleads southeast and then northeast to a point on the Snake River about 2 mi (3 km) above the mouth of Sinker Creek. A single lane track on the north

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