Chapter 1: Tectonic History of British Columbia: Historical and Current Influences on the Chilko-Chilcotin-Fraser River System

Abstract
The modern landscape of British Columbia is the result of hundreds of millions of years of tectonic processes, such as the prolonged subduction of oceanic lithosphere and subduction- related volcanism, the accretion of various microplates and terranes, and rapid uplift. Each of these forces has exacted long-term effects on the topography and morphology of the landscape, as is currently seen in the five “morphogeologic” belts of B.C. (e.g., Gabrielse et al, 1991; Figure 1a). The influence of tectonic processes on the Chilko-Chilcotin-Fraser River (CCR) system of British Columbia is particularly pronounced: as the landscape evolved, various paleo-drainages switched directions, rapidly incised and infilled older valleys, experienced rapid uplift, and interacted with voluminous volcanic and glacial deposits. Here, I analyze how the (1) large-scale and long-term tectonics and (2) smaller-scale regional geologic and geomorphologic drivers have influenced the development of the CCR system in the last 100-1 Ma. Though these processes may have only an indirect effect on local ecosystems along the modern rivers, they ultimately control the geomorphic and hydrologic landscapes of southern British Columbia. Therefore, they exert a major influence on the long-term evolution of the entire river system and the biotic systems within it.