Geology Reference
In-Depth Information
Basin and Range
Physiography
The elongate Basin and Range physiographic
province can be traced into Utah, Nevada, Idaho,
Oregon, Arizona, California, New Mexico, and Mexico
encompassing an area of 300,000 square miles and
comprising approximately 8% of the United States. Of
this vast province, only the northern, butterfly-shaped
area, primarily covering Nevada with small projections
into Utah, Idaho, California, and Oregon, forms the
Great Basin. The northwest extension of the Basin and
Range province into southern Oregon is bordered on
the west by the Cascade Mountains, on the north by
the High Lava Plains, and on the east by the Idaho
border, although the characteristic topography contin-
ues into Idaho. This region, which includes the stratigr-
aphically similar Owyhee Uplands on the east, forms
the southeast quadrant of the state and figures impor-
tantly in Oregon's geologic history.
As the name implies, the Basin and Range is
a series of long and narrow, north-south trending fault-
block mountain ranges alternating with broad basins.
Prominent physiographic features from west to east
across the province are Klamath Lake basin, Goose
Lake valley, Winter Rim, Summer Lake, Chewaucan
Basin, Abert Lake basin, Abert Rim, Warner Valley
basin, Warner Peak and Poker Jim Ridge, Hart Moun-
tain, Catlow Valley, the Steens and Pueblo mountains,
the Alvord basin, and the broad Owyhee Valley. Most
of the province is more than 4,000 feet in elevation.
The crest of Steens Mountain, at 9,670 feet above sea
level, is the highest and most scenic of Oregon's fault-
block peaks. Extending northwesterly for 50 miles, the
Steens merges to the south with the Pueblo Mountains.
East of Warner Valley, Warner Peak rises to 8,065 feet,
while Hart Mountain, the best defined fault-block
mountain in the United States, is 7,710 feet high. To
the west the sheer escarpments of Abert Rim and
Winter Rim rise dramatically more than 2,000 feet
above the valley floor.
The Great Basin, that portion of the Basin and
Range which includes Oregon, was first named in 1844
by explorer John Fremont who recognized that the
basin had no direct outlets to the sea, ending 20 years
of speculation on the course of waterways in the
region. In what is called the Oregon Great Basin, only
the Klamath and Owyhee rivers indirectly reach the
sea, although Goose Lake has been known to overflow
into the Pit River during historic times. In the western
portion of the Great Basin, the Klamath River origi-
nates in Upper Klamath Lake to flow from the extreme
southwestern edge of the province into California.
The Owyhee Uplands lies in the northwest
corner of the Great Basin. This region differs from the
rest of the province in that it is a flat deeply dissected
plateau with little interior drainage where fault-block
topography is less pronounced. The drainage basin of
the Owyhee River encompasses the uplands. Originat-
ing in Nevada, the Owyhee River flows northerly
through Idaho and Oregon to join the Snake River
near Adrian, Oregon. In spite of low rainfall in the
area, steep gradients give the the river and its tributar-
ies well-defined drainage patterns and deep canyons.
Cutting through the uplands over 6,000 feet above sea
level, the river drops to approximately 2,000 feet where
it joins the Snake. Small streams flowing in from the
hills are largely intermittent.
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