July 1993 - Oregon Department of Geology and Mineral Industries

locks of sill that would have resulted when pieces of
the rim broke off were not present. Scattered rounded
boulders were present throughout the material. Sills in
the Coast Range are quite stable, and at no place in the
study area could the rounded heads of streams be attributed
to sliding of sizable masses of gabbro. The writer
now has assigned the unconsolidated material to glacial
delivery and not to landslides.
LAUREL MOUNTAIN
Laurel Mountain is in the northern part of the Valsetz
quadrangle (Figure 3). It is the slightly upturned edge of
a large sill that extends southward to Fanno Ridge overlooking
Valsetz and westward from the vicinity of Riley
Peak into the Euchre Mountain quadrangle. In many
places, the sill is 400 or 500 ft thick but even thicker at
Fanno Ridge. The area is accessible by private road that
extends westward from Black Rock on the Little Luckiamute
River and utilizes an abandoned railroad grade past
Riley Peak to Boulder Camp. an abandoned logging camp.
Figure 2. Cirques (outlined) in SE corner of the Marys Peak quadrangle. A road continues through Boulder Pass and on down Mill
Creek to Buell in the broad Yamhill
River valley.
One of the best developed cirques
lies east of Boulder Camp, in the
SEY4 sec. 19, R. 7 w., T. 7 S. This is
the only cirque where some relatively
well-developed lateral moraines were
seen. The road down Mill Creek cuts
through the lower end of one of the
lateral moraines at about one mile
from Boulder Pass. The moraine on
the northwestern edge of the cirque is
better developed. The presence oflateral
moraines points to the movement
of glacial ice. Since the cirque basins
are short, seldom reaching half a mile
in length, the ice should have been
pushed over the edge, tumbled down
the steeper parts of the stream gradient,
and melted at the foot of the
slope. One would expect to find glacial
morainal material at the lower
levels. Although boulders of gabbro a
foot or two in diameter are common,
appreciable morainal material at the
lower levels is present only on the
lower slopes of Marys Peak.
Figure 3. Cirques (outlined) in north-central part of the Valsetz quadrangle.
Figure 4. Cirques (outlined) in southernmost part of the Grand Ronde and Hebo quadrangles.
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OREGON GEOLOGY, VOLUME 55, NUMBER 4, JULY 1993