The Lost Creek Designated Ground Water Basin (Lost Creek basin) is an important alluvial aquifer for irrigation, public supply, and domestic water uses in northeastern Colorado. Urban growth in the adjacent Front Range urban corridor has increased demand for groundwater in the basin, and potential exportation of groundwater from the basin has raised concerns about the long-term sustainability and management of the basin's groundwater resources. Beginning in 2005, the U.S. Geological Survey, in cooperation with the Lost Creek Ground Water Management District and the Colorado Water Conservation Board, collected hydrologic data and constructed a numerical groundwater flow model of the Lost Creek basin. The steady-state model builds upon the work of previous investigators to provide an updated tool for simulating the potential effects of various hydrologic stresses on groundwater flow and evaluating possible aquifer-management strategies.