9

The net result of these daily showers that dissipate as they move east-
ward is a much heavier precipitation in the western than the eastern part
of the map-area; the effect of this can be seen in the greater abundance of
glaciers in the west. From the character and profusion of the vegetation,
the amount and distribution of perennial ice and snow, and the texture of
drainage and average size of streams, it is estimated that precipitation in
the eastern and northeastern parts of the map-area may be of the order
of 20 inches a year or less, whereas in the western and southwestern
parts it is probably more than 50 inches. The average depth of snow in
the Pelly Lake and lower Ingenika River districts is reported! to be
between 2 and 4 feet; farther east and north it is even less, and horses are
wintered regularly on open range in the Rocky Mountain Trench 100 miles
north of the map-area, where the floor of Kechika River Valley is free of
snow at intervals throughout much of the winter. In contrast, in the south-
central and western parts of the area, 12 feet of snow have remained on the
ground in April at the Vega mineral claims, elevation 4,200 feet?; and on
July 17, 1947, 8 feet of snow still covered some of the veins on the Shell
mineral claims in the Croydon Creek district. Three weeks later this snow
had disappeared. The yearly increment of the névé fields at the head of
Abraham Creek and around Ferriston Creek, as seen from the annual
stratification exposed in the highest crevasses of the glaciers proper, is
between 5 and 8 feet. Taking 0-82 as the average density at which the
transition from snow to ice takes place, this would correspond to a precipi-
tation, in excess of that lost by summer wastage, equivalent to 50 to 90
inches of water during the snow accumulation season.

The ice on the rivers and large lakes usually breaks up about the third
week in April. The high-water period in the main rivers is usually quite
long, and commonly occurs in late June and early July. In 1948, an
abnormal year, an extreme flood stage was reached in late May. Snow
banks remain in the lee of ridges throughout the summer in all parts of the
area, but as a rule the highest ridges are bare enough for effective prospect-
ing by the first week in June. About this time also, the meadows at lower
elevations contain sufficient grass to support pack animals. The prospecting
season usually lasts until about the first week of October, although at
higher elevations severe snow-storms may be encountered any time in
September. The larger rivers and lakes are usually frozen sufficiently to
enable ski-equipped aircraft to be used in early December.

SOIL

All vegetation in the area, except the lichen and moss on rock out-
crops, is growing on recently transported material. This material, con-
sisting of colluvium from the valley slopes, glacial drift, and alluvial
deposits, is still undergoing transportation, or periodic erosion and deposi-
tion, over almost the entire land surface. Consequently, areas in which a
zonal soil profile has begun to be established are very limited. The most
prolific plant growth is found on the flood-plain floors of the larger river
valleys, and on lake deposits. The material deposited on the flood plains

1 William Isaac, Indian trapper on Ingenika River, personal communication, 1947.
2 Note on cabin door, Vega mineral claims.