Timber Butte obsidian

Timber Butte is the most heavily used obsidian source in western and central Idaho. It sits about 65 km north of Boise, west of the Payette River near Gardena, where the Idaho Batholith meets the Columbia River Basalt Group. At about 14.5 million years it is the oldest obsidian-bearing rhyolite dome in southern Idaho. It is a small intrusive dome, formed when the heat of rising Columbia River basalt magma partly melted the granite crust of the Idaho Batholith. The Nevada highway department's source catalog describes a band of obsidian outcrop and float in the Squaw Creek Valley, in Boise and Gem counties. The glass has distinctly low strontium, yttrium, niobium, zirconium and barium, which helps a lab separate it from other Idaho sources.

An intrusive rhyolite dome about 14.5 million years old, formed by melting of shallow granitic crust of the Idaho Batholith when the parent magma of the Columbia River Basalt Group upwelled. It lies west of the Payette River near Gardena, at the western contact between the Idaho Batholith and the Columbia River Basalt Group.