Unified Interior Regions

Region 9: Columbia-Pacific Northwest

Regions L2 Landing Page Tabs

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Broken Top volcano, inactive since 150 ka or longer, viewed to the ...

Broken Top volcano, inactive since 150 ka or longer, viewed to NW. ...

Radially dipping strata of the cone include subequal proportions of lava flows and flow breccias and of proximal agglutinate and scoria falls, nearly all having 54 to 56 percent SiO2. Numerous mafic dikes and sills intrude the cone, and an apron of compositionally similar mafic lavas extends far outward from the cone. Skyline crags behind buttress at right are top of a

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Topographic map, Mount St. Helens, C.E. 1919 annotated with locatio...

Topographic map, Mount St. Helens, C.E. 1919 annotated with locatio...

Due to the cataclysmic eruption of May 18, 1980, many of the locations annotated on this map are now either covered or no longer visible.