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now a conspicuous through valley, not well shown on the topographic map,
that lies about 2 miles west of Uslika Lake and includes parts of the valleys
of Vega Creek and the south branches of Tenakihi Creek, and that joins
the upper Osilinka-Discovery Creek trough near Chudelatsa Lake. To
the north, the next major pre-Glacial valley was the smooth trough now
occupied by the lower section of Osilinka River and the main part of
Tenakihi Creek, with tributaries that probably included the large stream,
now flowing to Tutizika River, west of Tenakihi Creek. At some earlier
date this drainage system may also have included the present Tutizzi Lake
Valley, but the available evidence suggests that Tutizika River had
established its connection with Mesilinka River considerably prior to the
beginning of glaciation.

The mouth of Tenakihi Creek is 315 feet below the level of Osilinka
River at the Aiken Lake winter road crossing, which is the lowest point
in the section of the upper Osilinka-Discovery Creek trough here under
consideration. The amount of glacial overdeepening, or the depth of fill, in
this trough and in the Tenakihi Creek-lower Osilinka trough is not known,
but it seems probable that the latter was already the lower valley in pre-
Glacial time. If this were so, conditions would be favourable for north-
flowing tributaries of the Tenakihi Creek-lower Osilinka Valley system to
advance headward and capture parts of the upper Osilinka-Discovery Creek
system. A stream in what is now Wasi Lake Valley made the greatest
headway, and it appears that, whether or not actual capture of the river
had been effected, a connection had been established, through this valley,
between the valleys of the upper and lower parts of Osilinka River before
occupation of the area by ice. A smaller tributary stream eroding south-
ward from what is now the mouth of Tenakihi Creek apparently had not
at this time cut through to the part of the valley now occupied by Uslika
Lake.

During a period of glaciation prior to the last advance of ice in this
area, the trunk glacier in the upper Osilinka-Discovery Creek trough sent
a distributary to the lower Osilinka Valley through Wasi Lake Valley,
which was smoothed and widened.

During retreat of the ice from this first advance, an extensive reces-
sional moraine was deposited in the upper Osilinka-Discovery Creek trough,
from the south end of Conglomerate Mountain to about 5 miles south of
the map-area. This moraine dammed Discovery Creek Valley, and to a
lesser extent Wasi Lake Valley, forming a lake that, apparently, drained
over the moraine dam into Wasi Lake Valley. The shore of this lake is
marked by the terraces on Conglomerate Mountain and southwest of
Uslika Lake. Vigorous stream erosion was resumed in the postulated inter-
Glacial period (or periods), and eventually a stream eroding southward
from the present mouth of Tenakihi Creek tapped the moraine-dammed
lake in what was then the upper Osilinka-Wasi Lake Valley drainage
system. Rapid down-cutting by the north-flowing pirate stream lowered the
lake to about its present level (Uslika Lake), and enabled small east-
flowing tributaries of the pirate stream, together with independent pirate
streams from what is now Tenakihi Creek, to capture segments of the
relatively large south-flowing stream in the valley 2 miles west of Uslika