The base-flow recession time constant (tau) is a hydrologic index that characterizes the ability of a ground-water system to supply flow to a stream draining from that system. The magnitude of tau indicates the degree of hydraulic conductivity of the stream to the groundwater system. Larger tau values indicate a stronger dependence on the groundwater system for streamflows, a smaller base-flow recession value indicates that the stream is not as dependent on the groundwater system for streamflows. Tau and other correlated hydrologic indices have been used as explanatory variables to greatly improve the predictive power of low-flow regression equations. Tau can also be used as an indicator of streamflow dependence on groundwater inflow to the channel. Tau values were calculated for 10 streamages in the Niobrara National Scenic River study area. This dataset contains the locations and calculated tau value at the streamgage.