This data release provides source code and an R workspace with functions comprising a non-linear baseflow separation model, calibrated values of parameters and estimates of the baseflow component of daily streamflow at selected streamflow gages. Parameter values were determined by calibration of the model. Estimates of the baseflow component include daily values and the total baseflow as a fraction of streamflow for the analysis period. The file 'run_bf_sep.zip' in the directory 'Nonlinear Baseflow Model Source Code, Functions, and Scripts" has a complete set of model functions, parameters for 13,208 USGS streamflow gages, and a script to run the model. Instructions and software requirements for running the model are described in the file README.txt