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The Pliocene to Late Neogene Bidahochi Formation, lies at an elevation of about to at the southeast of the Colorado Plateau; the deposits are from Bidahochi Lake, (also called Hopi Lake), and the deposits extend southwards to the region at the north perimeter of the White Mountains of central-east Arizona. Bidahochi Lake is thought to have been a single "large lake, or several shallow, and ephemeral ones."〔Lucchitta, 2001. ''Hiking Arizona's Geology'', Hike 11, ''Coliseum Diatreme'', pp. 116-119, p. 117.〕 Various fossil types are found; also bird trackways. The Bidahochi Formation is a cliff-former unit, and exists on the Colorado Plateau as a protecting unit above the highly erodable Chinle Formation. Locally it immediately overlies other rock units. The Bidahochi Formation extends approximately 112-mi〔Chronic, Halka, 1983. ''Roadside Geology of Arizona,'' roadtrip: ''Interstate 40 – Petrified Forest to New Mexico,'' pp. 210-212, p. 210.〕 north-south, or north-northwest by south-southeast; the length is approximately equivalent to today's Great Salt Lake of Utah. The presence of the Bidahochi Formation is a result of two factors. First it lies upon the major water divide of the (south perimeters) Chinle Wash (Chinle Valley) which flows north into the Colorado River watershed; it contrasts with the watershed to the west and south, the Little Colorado River, and the Puerco River tributary from New Mexico; the Defiance Plateau bordering the east of the Bidahochi, sheds water north, west, and south. The second is the timeframe of the Colorado River drainage through Grand Canyon, known to be about 5.5 Ma, where 5.5 Ma marks the beginning of the last deposits in the Bidahochi. The Bidahochi contains, Lower, Middle, and Upper sections, thus the drainages at the beginning of the Colorado River through Grand Canyon is coeval with the end of Bidahochi Lake deposition. ==Neogene Colorado Plateau geology== The present geologic status of most of the Colorado Plateau is in a sequence of erosion, caused by wind, water, and time; it is termed an unconformity, since river drainages are removing erosion products from the landscape. Late Paleogene geologic activity continued on the Colorado Plateau (Henry, Abajo, and La Sal Mountains);〔Blakey, Ranney, 2008. ''Ancient Landscapes of the Colorado Plateau'', pp. 118-119.〕 it continued into the Early Neogene at the San Juan Mountains of southwest Colorado.〔Blakey, Ranney, 2008. ''Ancient Landscapes of the Colorado Plateau'', p. 119.〕 Neogene volcanic activity was active on the Colorado Plateau. It ranged from the entire perimeter around the plateau, but also Kaibab Plateau at Grand Canyon, San Francisco Peaks (still active, Sunset Crater), and extended southeast to the Mogollon-Datil volcanic field. Besides alluvial deposits, or Quaternary sand dune deposits, the Bidahochi is possibly the sole geologic formation, that is non-volcanic in origin, during the Neogene, on the Colorado Plateau; it is at least one of the largest, non-volcanic in the Neogene on the plateau. 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「Bidahochi Formation」の詳細全文を読む スポンサード リンク
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