5. Ignimbrite of the climactic eruption (unit cf) at Godfrey Glen (left center) on Munson Creek where it meets Annie Creek (below photograph), viewed from turnout on Highway 62. Deposit (~100 m thick) is compositionally zoned: juvenile blocks are uniform rhyodacite pumice in lower part, andesitic and gabbroic scoria in upper part, with a mixed zone in between. Color reflects emplacement temperature and compositional zonation of particulate matrix; stratigraphically higher and hotter material is dark gray. Thin, light-colored layer at top is the pyroclastic-flow deposit where it has been bleached by fumarolic alteration beneath a 1- to 2-m-thick layer of fine ash. Pinnacle landforms in middle portion of ignimbrite are relatively erosion resistant tuff indurated by precipitation of silica and other minerals in pore spaces near gas-escape fractures and chimneys during cooling. High points on skyline are Garfield (left) and Applegate (right) Peaks on south caldera rim 6 km north-northeast of photographer.
Photograph by Charles R. Bacon.