1:24,000 SCALE MAPPING REVEALS DYNAMIC AND CLIMATIC LANDFORMS RIDING A KINEMATIC WAVE ALONG THE BURNT RIVER, BAKER COUNTY, NORTHEAST OREGON

Quaternary landforms along a 70 km reach of the Burnt River in northeastern Oregon were mapped at 1:24,000 scale to elucidate possible tectonic and climatic influences on fluvial processes in the region. The Burnt River cuts across Paleozoic and Mesozoic metamorphic rocks from the accreted Baker and Olds Ferry terranes. Sections of the catchment also contain Mio-Pliocene Lake Idaho sediments. Our study identified fluvial terraces formed as a result of Quaternary scale climatic oscillations, fault ruptures, or possibly larger scale dynamic topography. We gathered new data on several normal faults exposed in the region, which are responsible for local basin formation through the late Pleistocene and perhaps early Holocene. The diversity of underlying lithologies results in a morphologically diverse catchment. Several large basins and two deep gorges punctuate the length of the Burnt River. Mapping and differential GPS elevations for strath surfaces integrated with tephra chronology and optically stimulated luminescence geochronology helped establish average Quaternary incision rates along the reach of interest. Initial geochronological constraints indicate approximately 90 m of punctuated fluvial incision within the past 500,000 years. Continuing changes in the Burnt River catchment may be tied to regional dynamics of uplift and subsidence that have occurred since the Miocene emplacement of the Columbia River Basalt flows in eastern Oregon.