Abstract
The rise of the Yellowstone plume coincided with a shift from orogenic collapse of the Cordillera to Basin and Range extension in the northern Rocky Mountains, yet its impact on regional uplift, sediment dispersal, and drainage patterns remains largely unexplored. Here, we present rock magnetic analyses from eight Oligo-Miocene sedimentary sections in southwestern Montana. Using two complementary datasets, we identify a sharp increase in magnetic mineral concentration immediately after the early Miocene unconformity [~20 million years ago (Ma)], concurrent with a shift in detrital zircon ages, indicating a major provenance shift. We identify bimodal volcanism of the Columbia River Basalt Group as the dominant Miocene source, requiring that the early Miocene Continental Divide lay ~400 kilometers west of its present position. This reorganization, driven by Yellowstone plume-induced uplift, persisted until at least 10 Ma. Our study provides geologically based, temporal, and spatial constraints on dynamic topography previously only estimated from modeling.