The diffusive and nonspecific nature of nonpoint source contaminants such as sediment makes their management and mitigation challenging. Conventional source‐based tracing techniques for sediment simply apportion downstream sediment load to diffuse upstream sources classified by a limited number of source types including underlying rock type, land cover, and/or erosion process. Here, we develop a grid‐based sediment tracing technique that improves the precision of source contribution estimates and enhances the granularity of sediment source maps. We test the proposed technique using source and suspended sediment samples collected from the Emu Creek Catchment (911 km2), south‐east Queensland, Australia. Geochemical tracers were employed to distinguish sediments derived from the heterogenous and complex underlying rock types. Importantly, the proposed technique provided a greater spatial resolution of the sediment sources by assigning sediment contributions into grid sources rather than the area‐specific source types.