Ore Bin / Oregon Geology magazine / journal - Oregon Department ...
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Ore Bin / Oregon Geology magazine / journal - Oregon Department ...
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LEGEND<br />
[',TtJ<br />
_.~C ,<br />
Cascade Volcanic<br />
rocks<br />
UeU<br />
Tyee Formation and<br />
younger marine<br />
sedimentary units<br />
B<br />
Umpqua Group<br />
[(eU:b]<br />
Roseburg Basa t t<br />
[ill]]<br />
Pre-Tertiary<br />
OREGON<br />
CAL I FORN I A<br />
o 10 20 MILES<br />
L . ===::J<br />
20 40 KM<br />
W b---, ~d<br />
Figure 1, Regional geologic map of southwestern <strong>Ore</strong>gon showing Umpqua Group and adjacent<br />
major rock units (modified from Wells and Peck, 1961, and Baldwin, 1976),<br />
Lookingglass Formation: In its type area, southwest<br />
of Roseburg, Baldwin (1974) has subdivided the<br />
Lookingglass Formation into three members: basal conglomerate<br />
and sandstone, middle siltstone and sandstone,<br />
and upper sandstone and conglomerate, Further<br />
south, where the Lookingglass oversteps the pre<br />
Tertiary, the middle unit becomes coarser; locally, it<br />
pinches out and interfingers with the upper and lower<br />
members. To the north, the Lookingglass, like the Roseburg,<br />
becomes finer grained, and the basal Lookingglass<br />
conglomerate is only locally present, as at<br />
Woodruff Mountain (Figure 2),<br />
Clasts in the Lookingglass conglomerate include a<br />
variety of plutonic and metamorphic rock types apparently<br />
derived from Klamath Mountains terranes, in contrast<br />
to the predominant basalt pebbles in the Roseburg<br />
136<br />
OREGON GEOLOGY, VOL. 42, NO.8, AUGUST 1980
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