Surficial geology, Deka Lake, British Columbia

Abstract

The Deka Lake map area (92P/10) lies within the Fraser Plateau of south central British Columbia. It is a region of rolling topography with an average elevation of approximately 1200 m above sea level. Most of the region drains to the west via Bridge Creek which ultimately turns to the north and east and drains into Canim Lake, Mahood Lake, Clearwater River, and North Thompson River. The region is predominantly underlain by till which consists of a poorly sorted diamicton with clasts of all size. Bedrock outcrops are rare and limited in extent. Till is overlain in places by glaciofluvial sediments which were deposited in meltwater streams at the end of the last glaciation. Glaciolacustrine sediments, deposited in glacial lakes which formed at the end of the last glaciation, were mapped in the Bridge Creek and Deka Lake valleys as well as in the tributary valleys of Sheridan and Bridge lakes. Lacustrine sediments are present at the periphery of modern lakes throughout the map area. These were deposited at a time when the lakes occupied a higher level. Modern streams sediments (alluvium) are present in extent large enough to be mapped in some of the valleys. Colluvial deposits including a few large landslides are mapped on steep slopes throughout the map area. During the last glaciation, probably at glacial maximum, ice was dominantly moving to the south southeast as recorded by flutings, crag-and-tails and drumlins (see for instance the region north and northwest of Bridge Lake). However, an earlier phase of ice flow to the southwest is recorded from the glacial striations. During deglaciation, the drainage through Bridge Creek was dammed and a glacial lake developed in that valley and its tributaries. Part of the region drained in a subglacial setting, as indicated by the corridor of glaciofluvial sediment, including eskers, east and northeast of Sheridan Lake.