The Saddle Mountains consists of an upfolded
anticline
In structural geology, an anticline is a type of fold that is an arch-like shape and has its oldest beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex up in which the hinge or crest is the ...
ridge of
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
in
Grant County Grant County may refer to:
Places
;Australia
* County of Grant, Victoria
;United States
*Grant County, Arkansas
*Grant County, Indiana
*Grant County, Kansas
*Grant County, Kentucky
*Grant County, Minnesota
*Grant County, Nebraska
*Grant Co ...
of central
Washington
Washington commonly refers to:
* Washington (state), United States
* Washington, D.C., the capital of the United States
** A metonym for the federal government of the United States
** Washington metropolitan area, the metropolitan area centered o ...
state. The ridge, reaching to 2,700 feet, terminates in the east south of
Othello, Washington
Othello () is a city in Adams County, Washington, United States. The population was 7,364 at the 2010 census, a 26 percent increase from 2000. It is located in the heart of the Columbia Basin Project, approximately southwest of Spokane. T ...
near the foot of the
Drumheller Channels. It continues to the west where it is broken at
Sentinel Gap
Sentinel Gap is a water gap formed by the Columbia River in the Saddle Mountains, near Mattawa, Washington, Mattawa in Washington (state), Washington state. The gap is "a water gap where erosion by the Columbia River was able to keep pace with fol ...
(a water gap through which the
Columbia River
The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...
passes) before ending in the foothills of the
Cascade Mountains
The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, ...
.
Saddle Mountains geology
The top exposed layer of
Columbia River Basalt Group
The Columbia River Basalt Group is the youngest, smallest and one of the best-preserved continental flood basalt province on Earth, covering over mainly eastern Oregon and Washington, western Idaho, and part of northern Nevada. The basalt grou ...
basalt in the Saddle Mountains is the Saddle Mountain Basalt, which ranges from 120 – 240 meters (400 – 800 feet) in thickness and is interspersed by sedimentary layers of the Ellensburg Formation. The Saddle Mountain Basalt is composed of the Umatilla Member flows, the Wilbur Creek Member flows, the Asotin Member flows (13 million years ago), the Weissenfels Ridge Member flows, the Esquatzel Member flows, the Elephant Mountain Member flows (10.5 million years ago), the Bujford Member flows, the Ice Harbor Member flows (8.5 million years ago) and the Lower Monumental Member flows (6 million years ago).
The
Cordilleran Glacier diverted the ancient route of the
Columbia River
The Columbia River (Upper Chinook: ' or '; Sahaptin: ''Nch’i-Wàna'' or ''Nchi wana''; Sinixt dialect'' '') is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, C ...
15,000 years ago, backing up water to create
Lake Spokane
A lake is an area filled with water, localized in a Depression (geology), basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the World Ocean, oce ...
. As the Okanogan lobe grew the Columbia was rerouted into the
Grand Coulee
Grand Coulee is an ancient river bed in the U.S. state of Washington. This National Natural Landmark stretches for about 60 miles (100 km) southwest from Grand Coulee Dam to Soap Lake, being bisected by Dry Falls into the Upper and Lower ...
. Flowing across the current Grand Coulee-
Dry Falls
Dry Falls is a scalloped precipice with four major alcoves, in central Washington scablands. This cataract complex is on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee, northern ...
region, the ice-age Columbia then entered the
Quincy Basin near
Quincy, Washington
Quincy is a city in Grant County, Washington, United States. The population was 7,543 at the 2020 census.
History
Geologic history
Quincy lies atop a part of the Columbia River Basalt Group which is overlain by Pleistocene outburst flood depo ...
and joined
Crab Creek
Crab Creek is a stream in the U.S. state of Washington. Named for the presence of crayfish, it is one of the few perennial streams in the Columbia Basin of central Washington, flowing from the northeastern Columbia River Plateau, roughly east o ...
at Moses Lake, following Crab Creek's course southward past the
Frenchman Hills
The Frenchman Hills are hills in Grant County, Washington, United States of America. The high point is . They are an anticlinal fold in the northeastern part of the larger Yakima Fold Belt. They likely take their name for one of the first non-na ...
and turning west to run along the north face of the Saddle Mountains, there to rejoin the previous and modern course of the Columbia River just above the main water gap in the Saddle Mountains,
Sentinel Gap
Sentinel Gap is a water gap formed by the Columbia River in the Saddle Mountains, near Mattawa, Washington, Mattawa in Washington (state), Washington state. The gap is "a water gap where erosion by the Columbia River was able to keep pace with fol ...
. It eroded the north face of the Saddle Mountains, creating the conditions for the
Corfu Slide.
[J Harlen Bretz, (1923), The Channeled Scabland of the Columbia Plateau. ''Journal of Geology'', v.31, p.617-649]
Geography
See also
*
Saddle Mountain National Wildlife Refuge
The Hanford Reach National Monument is a national monument in the U.S. state of Washington. It was created in 2000, mostly from the former security buffer surrounding the Hanford Nuclear Reservation. The area has been untouched by development or ...
*
List of mountain ranges in Washington
There are at least 64 named mountain ranges in the U.S. state of Washington. Names, elevations and coordinates from the U.S. Geological Survey, Geographic Names Information System and trail guides published by The Mountaineers. Some of the ran ...
References
External links
Washington State Park link*
{{Authority control
Mountain ranges of Washington (state)
Landforms of Grant County, Washington