Geology Reference
In-Depth Information
around the park.
The 15 falls of the park were of more recent
origin. Whereas the large streams easily cut through
the basalts, the smaller creeks with less volume cannot
wear down through the rock as quickly. As larger
streams erode deep canyons, the smaller ones are left
high above to spill over the uncut basalt as waterfalls.
The largest cataract is South Falls, dropping 177 feet
into a beautiful, deep plunge pool. At North Falls, with
a height of 136 feet, the fossiliferous sandstone layer of
the Scotts Mills Formation under the basalt wears away
easily to create a 300 foot ampitheater behind the falls.
The chimney-like holes in the overhanging rock are
lava-cast tree molds where hot flowing lava surrounded
and engulfed standing tree trunks. Once the lava had
cooled, the tree decomposed, leaving only a mold of
the trunk.
the top on the south face. A dissected remnant of late
Miocene or early Pliocene lava flows, Table Rock is
capped by several isolated pieces of basalt. Columnar
fractures in the lava and adjacent isolated fragments on
surrounding peaks demonstrate the volcanic extrusive
nature of the features. Flow rocks here represent a
later sequence in development of the Western Cascades
that took place before the extrusion of the High
Cascades.
Suggested Readings
Allen, John E., Burns, Marjorie, and Sargent, Sam
C, 1986. Cataclysms on the Columbia. Port-
land, Oregon, Timber Press, 211p.
1982. The volcanic story of the Columbia River
gorge. Jour. Geol. Ed., v.30, p.156-162.
Allison, Ira S., 1935. Glacial erratics in Willamette
Valley. Geol. Soc. Amer., Bull., v.46, p.615-
632.
1978. Late Pleistocene sediments and floods in
the Willamette Valley. Ore Bin, v.40, no.11,
p.177-191; 193-202.
Baldwin, Ewart M., 1957. Drainage changes of the
Willamette River at Oregon City and Oswe-
go, Oregon. Northwest Sci., v.31, no.3,
pp.29-30.
Balsillie, J.H., and Benson, G.T., 1971. Evidence for
the Portland Hills fault. Ore Bin, v.33, no.6,
p.109-118.
Couch, Richard W., and Johnson, Stephen, 1968.
The Warner Valley earthquake sequence:
May and June, 1968. Ore Bin, v.30, no.10,
pp.191-204.
Freed, M., 1979. Silver Falls State Park. Oregon
Geology, v.41, no.l, p.-3-10.
Glenn, Jerry L., 1956. Late Quaternary sedimentation
and geologic history of the north Willamette
Valley, Oregon. PhD., Oregon State Univ.,
231p.
Graven, Eric P., 1990. Structure and tectonics of the
southern Willamette Valley, Oregon. Ms.,
Oregon State Univ., 119p.
Hanson, Larry G, 1986. Scenes from ancient Port-
land. Oregon Geology, v.48, no.11, p.130-
131.
Heaton, Thomas H., and Hartzell, Stephen H, 1987.
Earthquake hazards on the Cascadia subduc-
tion zone. Science, v.236, pp.119-168.
Jacobson, Randall S., et al., 1986. Map of Oregon
seismicity, 1841-1986. Oregon Dept. Geol.
and Mineral Indus., Geological Map Series,
Table Rock
Standing out on the skyline about 35 miles east
of Salem, Table Rock towers over the Western Cas-
cades. The steep cliffs of the peak, shaped like a
cardinal's hat, are easily visible and readily identified
from far out in the Willamette Valley. Reached by an
easy drive from Molalla, access to the crest of the
monolith is by a well-maintained hiking trail through
a dense forest that begins on the north face and winds
almost completely around the mountain to ascend to
Offering a panorama of the Willamette Valley, Table
Mountain east of Salem is a series of buttes
capped by basalts.
