42 RECONNAISSANCE IN NORTHERN ALASKA IN 1901. 



ANCIENT PLATEAU FEATURE OF BNDICOTT MOUNTAINS. 



Where best observed on this reconnaissance, principally on John and Anaktuvuk 

 rivers, a view across the top of the range presents the general appearance of an 

 ancient plateau or peneplain from which, by deep dissection, the mountains have 

 been carved. The former surface of the plateau is evidenced by numerous closely 

 crowded peaks, rising- generally to an elevation of 6,000 feet, where they present an 

 even sky line, as shown in PI. VII, A and B. For this plateau feature of the range 

 the name Endicott Plateau is proposed. About 4,000 feet below this level lie the 

 floors of the main valleys, at an elevation of about 2,000 feet; and the open Anaktuvuk 

 Pass, near the northern edge of the range, between John and Anaktuvuk rivers, is 

 at an altitude of scarcely 2,500 feet. 



Since for geologic purposes the accompanying geologic section (see section 

 on PI. Ill) is confined to the line of traverse along the vallej's, where the elevation 

 has been much reduced by erosion, the profile of the section does not express the pla- 

 teau character of the range. This feature is probably best shown in the illustrations 

 forming PI. VII, which are reproduced from photographs taken on the upper part 

 of John River, near the top of the range, at an elevation of about 6,000 feet. 



It seems to the writer not improbable that, as our knowledge of the physical 

 geography of Alaska becomes more complete, it will be found that the Endicott 

 Plateau, including its extension to the east, possibly beyond the Davidson Moun- 

 tains, may be correlated with the Chugach Plateau, a similarly dissected plateau 

 surface, which is observed in the westward continuation of the St. Elias Range, at 

 an elevation of about 6,000 feet/' 



The interstream areas, which in general rise to the surface of the Endicott Plateau, 

 are rarely flat topped, but consist of a network of peaks connected by irregular and 

 often sharp-crested ridges. Onty occasionally does an isolated peak rise a little 

 above the general level of the plateau. None that could be observed are monadnocks. 



The relation of the Endicott Plateau to the supposed Yukon and Koj'ukuk 

 plateau features, to be considered later, is diagrammatically illustrated in fig. 2 (p. 44). 

 So far as known, no rocks younger than Lower Carboniferous have been found in 

 the Endicott Plateau. But as it seems not improbable that Upper Carboniferous 

 and possibly even Lower Mesozoic rocks may be present in the Fickett series, it 

 does not seem safe to suggest for the plateau an age earlier than Mesozoic. It seems 

 undoubtedly older than the supposed Yukon Plateau, which in turn is considerably 

 older than the Koyukuk Plateau, as the latter lies at a much lower level and is com- 

 posed of rocks which are in part Cretaceous, and some possibly younger. 



a Schrader, F. C, and Spencer, A. C, Geology and Mineral Resources of a Portion of the Copper River District, Alaska; 

 a special publication of the U. S. Geol. Survey, 1901. 



See also Schrader, F.C., A reconnaissance of a part of Prince William Sound and the Copper River district, Alaska: 

 Twentieth Ann. Rept. U. S. Geol. Survey, pt. 7, 1900, p. 375. 



