Located in northwest Boulder County, Colorado, in the Front Range of the Rocky Mountains, the Lefthand Creek watershed drains an area of approximately 220 km. Lefthand Creek, James Creek, and Little James Creek are the primary streams in the watershed, producing an average total discharge of about 25,000 acre-feet per year, where Lefthand Creek drains from the foothills onto the plains near Highway 36. Lefthand Creek serves as a key water supply—and the only winter water source—for the 18,000 residential customers of the Left Hand Water District. Additional water users include watershed residents, agricultural shareholders of the Left Hand Ditch Company, and Boulder County Parks and Open Space. Diverse land use and land cover in the watershed include national forest land, residential, and recreational areas in the forested mountains and foothills in the western portion of the drainage, transitioning to agriculture and semi-urban areas in the eastern plains region of the watershed. Situated in the northern tip of the Colorado Mineral Belt, a highly mineralized region that stretches northeast from the San Juan Mountains, the Lefthand Creek watershed formerly hosted wide spread hardrock mining and milling operations. Beginning in the late 1850s, mineral extraction and processing occurred at hundreds of sites in the watershed (Cobb, 1988; EPA, 2003a). The most recent mining activity ceased in the mid-1990s, and no mines or mills currently operate in the watershed.