In 2006, a cooperative study was established to compile reliable data describing groundwater and surface-water interactions in the Elkhorn and Loup River Basins. The purpose of the study was to address state legislation that requires a sustainable balance between long term water supplies and uses of surface water and groundwater. A groundwater-flow model [hereinafter referred to as the Elkhorn-Loup Model (ELM)] was constructed as part of the first two phases of that study as a tool for understanding the effect of groundwater pumpage on stream base flow and the effects of management strategies on hydrologically connected groundwater and surface-water supplies. The third phase of the study was implemented to gain additional geologic knowledge and update the ELM with enhanced water-budget information and refined discretization of the model grid and stress periods. As part of that effort, the ELM is being reconstructed to include two vertical model layers, whereas phase-one and phase-two simulations (Peterson and others, 2008; Stanton and others, 2010) represented the aquifer system using one vertical model layer. The goal for defining the base of the upper model layer was to divide the model vertically so that the upper layer had different water transmitting and storage characteristics than the lower layer. Texture descriptions were used in most cases to identify the depth in a test-hole, water well, or surface-geophysical log at which dividing the aquifer produced contrasting texture characteristics for the upper and lower model layers. The study area covers approximately 30,000 square miles, and extends from the Niobrara River in the north to the Platte River in the south. The western boundary roughly coincides with the western boundary of the Upper Loup NRD, and the eastern boundary roughly coincides with the approximate location of the westernmost extent of glacial till in eastern Nebraska (University of Nebraska, 2005). This data release consists of a line shapefile of contours attributed with values representing the elevation of the base of the upper layer of the two-layer phase-three ELM above the vertical datum (National Geodetic Vertical Datum of 1929).