8

and gorges near their mouths. Such a gorge is best exemplified on Lay
Creek, where it has a length of 74 miles and a maximum depth in excess
of 450 feet; other good examples are found on Polaris, Pelly, and Haha
Creeks and on the south branch of Wasi Creek. Some tributary streams,
as for example Cutbank, Abraham, and Matetlo Creeks, have developed
only small canyons, but have extended their channels as much as 2 miles
out into the main valleys on large alluvial fans.

The larger lakes are confined to the lower valleys, and are dammed
chiefly by glacial deposits or alluvial fans of tributary streams. _Innumer-
able rock-basin and moraine-dammed lakes and tarns occur in cirques
and hanging valleys at and above timber-line.

The map-area at present contains glaciers only in the west and
southwest, and even within these parts perennial ice covers only about
8 per cent of the area. Drainage by ice is thus restricted to numerous,
scattered, small cirques and basins, and to a few sheltered valleys in which
glaciers reach down to timber-line.

CLIMATE

No weather records have been kept within the map-area. In general
the climate appears to be similar to that of much of the northern interior
of British Columbia, with probably a heavier precipitation than in the
Nechako Plateau to the south, the Spatsizi Plateau to the north, or the
Rocky Mountains to the east. The summers are moderate, and frosts are
rare in the main valleys between June and the latter part of August. The
winters are relatively cold, usually bright and clear, and occasionally
subject to periods of intensely cold, clear weather. The extremes of
temperature in the valleys are probably similar to those recorded by
Stanwell-Fletcher (1943) in Driftwood River Valley to the west, namely,
a maximum of about 95° F. and a minimum of about —60°F.

The precipitation appears to be fairly well distributed throughout the
year, with a slight maximum in autumn and early winter, and a minimum
in late winter. Although prolonged storms are not unknown, the area is
somewhat unique in that in both summer and winter the precipitation is
mainly from small scattered showers and flurries of short duration. On
almost every day in summer the view from a high summit will disclose
several, sometimes as many as a score, small individual rain-storms sweeping
across the country from west to east. Most of the showers appear to
originate in persistent cloud banks over the Sustut Peak and Bear Lake
districts of McConnell Creek map-area to the west (Lord, 1948, p. 5); from
them, individual cloud masses are detached and drift over Aiken Lake
map-area at elevations of 8,000 to 12,000 feet. Most of the showers end
before completely crossing the area; few reach the Rocky Mountain
Trench. During the summer of 1947, for example, rain fell in 38 out of
42 days in Ingenika River Valley, but no storm was of more than 2 hours
duration, and most lasted less than 4 hour; the days were almost without
exception warm and sunny. In this area almost all of the showers passed
over in the late afternoon. In contrast, all-day rains are not uncommon at
Croydon Creek.