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Abstract Dietrich River and hiking 5 mi (8 km) to ridges northwest of Kuyuktuvuk Creek and Trembley Creek (an elevation gain of 2,000 to 3,000 ft [600 to 900 m]), a visitor gains access to some of the major stratigraphic units exposed in the fenster and at the base of the allochthon. However, in this area, exposures are not as good, and the structure is much more complicated than in the area of Mount Doonerak and Amawk Creek to the west. Only the base of the Endicott Mountains allochthon is present in the area of the Doonerak fenster. The upper part of the Upper Devonian elastic sequence and the Mississippian to Trias-sic rocks on the allochthon are best exposed from the Brooks Range crest at Atigun Pass north to the mountain front, and are most easily reached from the Dalton Highway in the northern Endicott Mountains. The Doonerak fenster is located in the central Brooks Range about 35 mi (55 km) south of the Endicott Mountains front. It can be traced for at least 70 mi (110 km) southwest from the Dalton Highway (the Trans-Alaska Pipeline haul road) about 50 mi (80 km) north of the village of Coldfoot. The area is located on the Wiseman and Chandalar 1:250,000 quadrangle maps and the Wiseman D1 and D2 and Chandalar D6 1:63,360 quadrangle maps. The most significant stratigraphic and structural relationships in the fenster and at the base of the overlying Endicott Mountains allochthon are best exposed near Mount Doonerak and in the canyon of Amawk Creek 15 to 22 mi (24 to 35 km) west of the Dalton Highway. These areas are most easily reached by helicopter, or by bush planes, which can be landed on a gravel bar near the junction of Bombardment Creek and the North Fork of the Koyukuk River. The area is within the Gates of the Arctic National Park, and permission for helicopter access must be obtained in advance from the Superintendent, Gates of the Arctic National Park, P.O. Box 74680, Fairbanks, Alaska 99707. The eastern end of the fenster is accessible by foot from the Dalton Highway from between miles 225 and 226. By wading the Dietrich River and hiking 5 mi (8 km) to ridges northwest of Kuyuktuvuk Creek and Trembley Creek (an elevation gain of 2,000 to 3,000 ft [600 to 900 m]), a visitor gains access to some of the major stratigraphic units exposed in the fenster and at the base of the allochthon. However, in this area, exposures are not as good, and the structure is much more complicated than in the area of Mount Doonerak and Amawk Creek to the west. Only the base of the Endicott Mountains allochthon is present in the area of the Doonerak fenster. The upper part of the Upper Devonian elastic sequence and the Mississippian to Trias-sic rocks on the allochthon are best exposed from the Brooks Range crest at Atigun Pass north to the mountain front, and are most easily reached from the Dalton Highway in the northern Endicott Mountains.

Abstract Dietrich River and hiking 5 mi (8 km) to ridges northwest of Kuyuktuvuk Creek and Trembley Creek (an elevation gain of 2,000 to 3,000 ft [600 to 900 m]), a visitor gains access to some of the major stratigraphic units exposed in the fenster and at the base of the allochthon. However, in this area, exposures are not as good, and the structure is much more complicated than in the area of Mount Doonerak and Amawk Creek to the west. Only the base of the Endicott Mountains allochthon is present in the area of the Doonerak fenster. The upper part of the Upper Devonian elastic sequence and the Mississippian to Trias-sic rocks on the allochthon are best exposed from the Brooks Range crest at Atigun Pass north to the mountain front, and are most easily reached from the Dalton Highway in the northern Endicott Mountains. The Doonerak fenster is located in the central Brooks Range about 35 mi (55 km) south of the Endicott Mountains front. It can be traced for at least 70 mi (110 km) southwest from the Dalton Highway (the Trans-Alaska Pipeline haul road) about 50 mi (80 km) north of the village of Coldfoot. The area is located on the Wiseman and Chandalar 1:250,000 quadrangle maps and the Wiseman D1 and D2 and Chandalar D6 1:63,360 quadrangle maps. The most significant stratigraphic and structural relationships in the fenster and at the base of the overlying Endicott Mountains allochthon are best exposed near Mount Doonerak and in the canyon of Amawk Creek 15 to 22 mi (24 to 35 km) west of the Dalton Highway. These areas are most easily reached by helicopter, or by bush planes, which can be landed on a gravel bar near the junction of Bombardment Creek and the North Fork of the Koyukuk River. The area is within the Gates of the Arctic National Park, and permission for helicopter access must be obtained in advance from the Superintendent, Gates of the Arctic National Park, P.O. Box 74680, Fairbanks, Alaska 99707. The eastern end of the fenster is accessible by foot from the Dalton Highway from between miles 225 and 226. By wading the Dietrich River and hiking 5 mi (8 km) to ridges northwest of Kuyuktuvuk Creek and Trembley Creek (an elevation gain of 2,000 to 3,000 ft [600 to 900 m]), a visitor gains access to some of the major stratigraphic units exposed in the fenster and at the base of the allochthon. However, in this area, exposures are not as good, and the structure is much more complicated than in the area of Mount Doonerak and Amawk Creek to the west. Only the base of the Endicott Mountains allochthon is present in the area of the Doonerak fenster. The upper part of the Upper Devonian elastic sequence and the Mississippian to Trias-sic rocks on the allochthon are best exposed from the Brooks Range crest at Atigun Pass north to the mountain front, and are most easily reached from the Dalton Highway in the northern Endicott Mountains.