184 W. N. THAVER 
deformed region, somewhat modified by glaciation. Some of the 
higher peaks are estimated to measure 8,000 feet, but the general 
vertical relief is from 3,000 to 4,500 feet. 
The eastern or newer range displays a marked difference in 
topography. Its structure is due to fracturing, buckling, and 
faulting, which has resulted in a more rugged and compact range of 
crumpled and tilted blocks. The highest peaks are roughly pyramid- 
shaped masses that reach elevations of 6,500 to 7,500 feet. Erosion 
has not reached such an advanced stage as in the western range. 
Keele’ regards the Mackenzie Mountains as closely related in 
both geology and structure to the Boundary Group, and, applying 
the various criteria used by physiographers, it would seem that this 
group may be definitely placed in the same classification as the 
Rocky Mountains. 
Just beyond the boundary between Yukon Territory and Alaska 
another mountain group rises and extends westward toward Bering 
Sea. The name Endicott Mountains, originally applied to a single 
range of this group, is now made to include the whole.? Brooks? 
correlates these mountains as an orographic continuation of the 
Mackenzie group and as a part of the great physiographic division 
of the Rocky Mountain System. 
The Endicott Mountains are sharply defined. They are 
bounded on the south by the Yukon Plateau and on the north by 
the Anatuvuk Plateau, a part of the Great Plains province. The 
southern slope rises rather abruptly from the uplands of the Yukon 
Plateau, though the line between the uplands and the mountains 
is irregular, at one point bending southward to include a spur, at 
another forming a deep re-entrant into the front of the range. On 
the Arctic slope the descent is still more abrupt. For long stretches 
the mountains present a bold escarpment to the north, and the 
sharp transition from the smooth, moss-covered (Anatuvuk) 
plateau to the bold, rugged mountains is very striking. 
So far as is known, the Endicott Mountains embrace at least 
two distinct ranges. ‘The topography is rugged and the transverse 
t Jos. Keele, Geol. Survey Canada, Pub. 1097, pp. 13-18 and pl. 3. 
2 F. C. Schrader, U.S. Geol. Survey, Prof. Paper 20. 
3 A. H. Brooks, of. cit., pp. 42-46. 
