|
The Oregon high desert is a region of the U.S. state of Oregon, located east of the Cascade Range and south of the Blue Mountains, in the central and eastern parts of the state. Divided into a southern region and a northern region, the desert covers most of five Oregon counties and averages above sea level. The southwest region is part of the Great Basin and the southeast is the lower Owyhee River watershed. The northern region is part of the Columbia Plateau, where somewhat more rainfall allows the largest industry on private land to be the cultivation of alfalfa and hay. Public land within the region is owned primarily by the Bureau of Land Management (BLM), which manages more than , including five rivers designated as Wild and Scenic. While the high desert is somewhat dry, it is only arid relative to Western Oregon. The region averages of annual rainfall; the Alvord Desert, however, gets only of rain each year. Contrary to its name, most of the high desert is not dry enough to truly qualify as desert, and biologically, most of the region is classified as scrubland or steppe. At above sea level, the summit of Steens Mountain is the highest point in the high desert. The broad fault-block mountain is characteristic of the basin and range plate tectonics of the high desert. About 16 million years ago, during the early Miocene epoch, lava flows from volcanic eruptions covered about half the surface area of Oregon. The Earth's crust then began stretching, giving way to further volcanic activity from 15 million to 2 million years ago. Several ice ages over this time formed the large lakes in the high desert. The climate of the high desert provides habitat for mammals such as pronghorn, coyote, mule deer, black-tailed jackrabbit, and cougar. Birds common in the region include sage grouse, California quail, and prairie falcon. The western juniper is the most common tree in the region, and big sagebrush and common woolly sunflower are the region's most widespread plants. ==Geography== The high desert of Oregon is located in the central and southeastern part of the state. It covers approximately , extending approximately from central Oregon east to the Idaho border and from central Oregon to the Nevada border to the south. Most of the region is located in Crook, Deschutes, Harney, Lake, and Malheur counties.〔〔〔Jackman and Long, p. 2〕 The high desert gets its name from its generally high elevation, averaging about across the region. It is bordered by the eastern foothills of the Cascade Range to the west. The Blue Mountains are the geographical boundary to the north, marking the northern end of the high desert's semi-arid plateau. The southern high desert is part of North America's Basin and Range Province, which extends south through Nevada and Arizona, into Mexico. It contains large alkali lakes and tall cliffs, some with a prominence of more than . Steens Mountain, in Harney County, is the highest point within the region; its summit is above sea level.〔〔McArthur, p. 912〕〔(【引用サイトリンク】title=Basin and Range province )〕〔(【引用サイトリンク】title=Columbia Plateau province )〕〔"Pluvial Lakes: Oregon's Inland Seas", ''Oregon: A Geologic History''〕 To the east, the high desert country of the Columbia Plateau extends across the Snake River and into Idaho.〔 A number of rivers flow through the high desert region. These include the Deschutes River and its tributary the Crooked River, as well as the Malheur, Owyhee, and John Day rivers, which are all within the Columbia River watershed. Since the high desert encompasses the portion of the hydrographic Great Basin located in Oregon,〔(【引用サイトリンク】title=High Desert )〕 smaller rivers in the high desert flow into closed basins. The Chewaucan River, the Donner und Blitzen River, and the Silvies River each flow into some of the high desert's salt lakes.〔〔Brogan, pp. 14–15〕〔(【引用サイトリンク】title=Owyhee Wild and Scenic River )〕〔Jackman and Long, p. 347〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High Desert (Oregon)」の詳細全文を読む スポンサード リンク
|