Nechako River Map-Area

The till grooves appear to be shallow linear grooves in an otherwise fea-
tureless till surface. They occur in areas of thick glacial debris or wherever the
bedrock surface does not have a controlling influence on the developed glacial
features. They are widely spaced and the intervening area bears no resemblance
to drumlins. These grooves may be compared to scratches in a till surface formed
by a few major irregularities in the base of the ice, which, for reasons unknown,
were maintained during glacier flow, or they may be vestiges of drumlins or rock
drumlin areas that have been almost obliterated by subsequent deposits.

All features mentioned point to a general ice movement in a direction vary-
ing from N40°E to east, and most drumlins, rock drumlins, and many glacial striae
‘clearly indicate a southwestern source of ice. Air photographs of the area show
that on some of the higher hills and in some protected areas another set of glacial
| grooves exists, indicating earlier ice movement quite different from that sug-
| gested for the last movement. On Uncha Mountain, near Grassy Plains, on Mount
Hobson, on Tatelkuz Mountain, and at several other places in the area linear
grooves vary in direction from N30°W to N10°E, but at no place is there con-
clusive evidence to show whether this ice moved northward or southward. A
recent study by the writer of the distribution of erratics near Alexis Creek, south-
feast of Nechako River area, has shown that an earlier north-to-south movement
of ice occurred in that area.

Eskers

Eskers are abundant throughout the area, more particularly in the south-
eastern half. For purposes of mapping they have been shown as two types: (1)
single eskers, the typical sinuous gravel ridge; and (2) esker complexes, reticulate
networks of ridges completely enclosing kettle-like depressions. The first type is
not unusual, the second is similar in most respects to the ‘compound eskers’ of
Carp Lake map-area to the northeast (Armstrong and Tipper, 1949). The term
esker complex is however more descriptive than compound esker, suggesting not

, only complexity of pattern but also complexity of origin.

The only esker complex of importance extends from the east end of Natal-
kuz Lake along Nechako River for 6 to 7 miles (see Pl. III). This network of
ridges is made up of porous and permeable gravel and sand, and rises as much as
275 to 300 feet above the river level, as it existed in 1950. The Aluminum Com-
pany reported a depth of about 300 feet of gravel and sand below the river level,
which means a total thickness, in places, of 600 feet. However, the drilling may
have penetrated relatively unconsolidated Tertiary gravel and sand similar to the
materials of the eskers but unrelated to them. The sides of the esker ridges are
steep, close to the maximum angle of repose for unconsolidated materials, and the
crests of the ridges are sharp and narrow. The depressions are round or elongated
parallel with the ridges, which in this instance parallel Nechako River. Although
the complex is in the Nechako River valley it cannot be considered as confined

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