US Forest Service 048 (US Forest Service 48), Clackamas Co., Oregon, USA

Age: Neogene (2.588 - 23.03 Ma)

Stratigraphic Name: Columbia River Basalt

Comments: Columbia Plateau

Lithology: Flood basalt(s); mafic volcanic rocks; basalt

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Age: Miocene (5.333 - 23.03 Ma)

Stratigraphic Name: Rhododendron Formation

Description: Tertiary andesitic rocks; andesite

Lithology: Major:: {pyroclastic rocks}; Major:: {volcanic diamictite}; Major:: {mudflow}; Major:: {debris-flow deposits}; Major:: {landslide}; Major:: {ash-flow ash}; Major:: {tuff breccia}; Major:: {na}; Major:: {andesite breccia} Minor:: {andesite flows}

Reference: R.L. Smith, W.P. Roe (compilers). Oregon Geologic Data Compilation, release 6. State of Oregon Department of Geology and Mineral Industries. [20]

Age: Miocene (7.246 - 20.44 Ma)

Description: Lava flows and flow breccia of hypersthene and olivine andesite, basaltic andesite containing plagioclase and pyroxene phenocrysts, and basalt; many flows contain phenocrysts of both hypersthene and augite. Includes interbedded volcaniclastic and epiclastic rocks mostly of andesitic composition, but partly of dacitic or rhyodacitic composition. Includes really restricted flows of silicic andesite or dacite. Upper part of unit mostly unaltered, although olivine crystals are locally altered to clay minerals. Lower parts commonly altered; secondary minerals include nontronite and saponite, chalcedony, calcite, and zeolites. Older parts of this unit locally are propylitically altered adjacent to larger intrusions. Erupted mostly from widespread, northwest- and north-trending dikes and dike swarms and related plugs and lava cones. Potassium-argon ages range from about 10 Ma to about 17 Ma. Much of this unit was previously assigned to the Sardine Formation (Peck and others, 1964), although the type locality of the Sardine Formation ("Sardine Series" as mapped by Thayer, 1939) may be older. Includes Elk Lake Formation (White, 1980a, 1980b), part of the Rhododendron Formation (Trimble, 1963; Wise, 1969), and andesite of Nohorn Creek of Hammond and others (1982)

Lithology: Major:{basalt,andesite,basaltic andesite}, Incidental:{dacite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]