The northern part of the Southeast Three Sisters quadrangle straddles
the crest of the central High Cascades of Oregon. The area is
covered by Pleistocene and Holocene volcanic and volcaniclastic rocks
that were extruded from a number of composite cones, shield volcanoes,
and cinder cones. The principal eruptive centers include...
The Summer Coon intrusive center is located seven miles
north of Del Norte, Colorado, on the eastern edge of the San Juan
Mountains. The intrusive center is the core of a dissected calcalkaline
composite volcano of middle Oligocene age. The Summer
Coon rocks belong to the Conejos Formation which is...
The thesis area is located southwest of Portland, Oregon, in the
Western Cascades. In the area are volcaniclastic rocks and lava flows
that range in composition from basaltic andesite to dacite. The dominant
volcaniclastic rock type is thin intracanyon ash-flow tuff. The
dominant lava flows are a thick sequence of...
During the Pleistocene, an andesitic volcano named Mount
Mazama grew to a probable elevation of 3000 meters in south-
central Oregon. Near the end of the Pleistocene, three diverse
magma types appeared in the eruptive products associated with Mount
Mazama: l)High-alumina basaltic andesite magma associated with an
early plateau and...
Castle Rocks is 12 miles east of Mt. Jefferson, in the central
Cascades of Oregon. The area contains volcanic rocks ranging from
mid-Miocene to Holocene in age. These rocks record alternating
periods of tholeiitic and calc-alkaline volcanism.
The oldest rocks in the area range from basaltic andesite lava
flows to...
