Map of Timber Hill basalt in the context of the Yellowstone hotspot track

Map of the northwestern U.S., showing the approximate locations of the Yellowstone hotspot volcanic fields (orange) and Columbia River Basalts (gray).  Boundary of Yellowstone National Park is shown in yellow.  Inset shows physiographic map of southwest Montana and central Idaho.  Major extensional faults are shown by black lines with balls-and-bars on down dropped block.  The Heise Volcanic Field and outcrops of the Timber Hill basalt are shown in red.  The interpreted flow path of the basalt is shown by the orange arrow.  Base figure by Zack Lifton (Idaho Geological Survey), with physiographic map by Jesse Mosolf (Montana Bureau of Mines and Geology).