Geology Reference
In-Depth Information
The Chalk Basin along the lower Owyhee River shows lake sediments covered by successive lava
flows (courtesy Oregon State Highway Department).
Pillars of Rome and Leslie Gulch
Approximately 4 miles northwest of the small
town of Rome in Malheur County, cliffs called the
Pillars of Rome have been cut into the deep canyon
where Jordan Creek merges with the Owyhee. Here
400 to 500 feet of Pliocene tuffaceous sediments filled
the Owyhee River valley during an alluvial period.
Since that time, erosion has cut through the beds to
create a badland topography of high, vertical pinnacles
and pillars that resemble Roman ruins.
Another outstanding feature produced by
erosion in this dry plateau are the jagged peaks and
columns at Leslie Gulch approximately 23 miles
directly south of Owyhee Dam. The narrow 10 mile
long canyon is traversed by a steep road that requires
the frequent use of brakes when descending from an
elevation of 4,600 feet to the Owyhee reservoir at 2,600
feet. Cut into Leslie Gulch ash-flow tuff, brown, cream,
and white minarets and spires extend throughout the
gorge. The stream-deposited tuffs are more than 2,000
feet thick in places and cover an area of about 100
square miles. The multi-colored volcanics were pro-
duced from eruptions of Mahogany Mountain, the
oldest caldera in the Lake Owyhee volcanic field, 15.5
million years ago.
Suggested Readings:
Allison, Ira, 1982. Geology of pluvial Lake Chewa-
ucan, Lake County, Oregon. Oregon State
University, Studies in Geology, 11, 78p.
Blackwell, David, et al., 1978. Heat flow of
Oregon. Jour. Geophys. Res., v.87, no.BlO,
pp.8735-8754.
Bowen, R.G., Peterson, N.V., and Riccio, J.F., 1978.
Low-to intermediate-temperature thermal
springs and wells in Oregon. Oregon Dept.
Geol. and Mineral Indus., Geol. Map. Ser.
GMS-10.
Castor, Stephen B., and Berry Michael R., 1981.
Geology of the Lakeview uranium district,
Oregon. In: Goodell, Philip, and Waters,
Aaron, Uranium in volcanic and volcanicla-
stic rocks. Amer. Assoc. of Petroleum Geol.,
Studies in Geology, v.13, pp.55-62.
Christiansen, Robert L, and McKee, Edwin H.,1978.
Late Cenozoic volcanic and tectonic evolu-
tion of the Great Basin and Columbia inter-
montane regions. In: Smith, Robert, and
Eaton, Gordon P., eds. Cenozoic tectonics
and regional geophysics of the western Cor-
dillera. Geol. Soc. Amer., Memoir 152,
pp.283-311.
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