13

CHAPTER III
PHYSIOGRAPHIC DEVELOPMENT
GENERAL STATEMENT

The landscape presented by Aiken Lake map-area is mainly one of
land forms produced or modified by glacial and glacio-fluvial processes
(Plate I). The detail of the present topography dates from the occupation
of the entire area by an ice-cover related to the Pleistocene continental
glaciers. The land surface left by the regional ice-cover has been modified
by subsequent alpine glaciation, frost action, and stream action to produce
the present land forms. All of these modifying processes are still active
within the map-area.

There are no extensive high-level erosion surfaces within the map-area.
The landscape is completely mature, in that all the upland area has been
reduced to slope, and essentially the entire area is being actively modified
by present geomorphic processes. The only evidence of a land surface
distinct from that being at present developed are a few remnants, totalling
less than 4 square mile, of the highly undulating surface vacated by the
regional ice-sheet. The surface exhibited by these small remnants may be
little different from the pre-Glacial erosion surface.

In common with many mountainous areas undergoing rapid degrada-
tion, the Omineca Mountains present a general accordance of summit
altitude, which in Aiken Lake map-area is between 6,500 and 7,200 feet
above sea-level (Plate II B). This broadly accordant summit level seems
to be due entirely to the relation between the effectiveness of erosional
agencies and the height of the peaks (Daly, 1912, pp. 631-641; von
Engeln, 1942, p. 99) rather than to any relation to a former erosion surface.

CHARACTER OF THE PRE-GLACIAL LAND SURFACE

Little direct evidence can be obtained from Aiken Lake map-area on
the character of the land surface in pre-Glacial times. Remnants of an
erosion surface older than the one being formed at present are too
fragmentary to provide any indication of the nature of the pre-Glacial
surface.

To the northwest, and to a lesser extent to the south, of the map-area,
however, the land surface vacated by the last regional ice-cover has been
much less dissected, and large areas of rolling upland, which grade into
the extensive plateaux of central and northern British Columbia, remain.
The physiographic history, as reconstructed in these areas (Dawson, 1891,
pp. 3-74; Lay, 1941, p. 68; Holland, 1940, p. 19; Hedley and Holland,
1941, p. 25; Watson and Mathews, 1944, p. 34; Lord, 1948, p. 4) suggests
that by late Tertiary time stream dissection had produced a mature
topography of moderate relief with a well-organized drainage system.
Holland (1940) and Lay (1941) have presented evidence for a late Tertiary
rejuvenation of stream action, and a period of canyon cutting immediately
preceding the advance of Pleistocene ice.