BackgroundVolcanism began approximately 3.2 million years ago with eruption of at least 650 meters of high-silica rhyolite tuff, which is exposed on the east flank of the subsequent Goat Rocks volcano.
Goat Ricks volcano itself was probably build between ca 2.5 - 0.5 million years ago. It produced large volume lava flows, most notably the 1.0 million-year-old Tieton Andesite, which reached ca. 80 kilometers eastward. It is the longest known andesite flow on Earth.
Source: Wood and Kienle, (eds.), 1990, Volcanoes of North America - United States and Canada: Cambridge University Press., cited on CVO website.
See also: Sentinel hub | Landsat 8