This dataset contains input parameter and data files, as well as output files for simulations prior to the distribution of parameters from near-native subbasins to uncalibrated hydrologic response units (HRUs) (pre-distribution) and after parameters are distributed to HRUs (post-distribution). Simulated and observed streamflow for sites along the mainstem of the Rio Grande River are included for parts of the Upper Rio Grande Basin in Colorado, New Mexico, Texas, and northern Mexico using the Precipitation-Runoff Modeling System (PRMS). Input data include pre-distribution input parameters for the entire Upper Rio Grande Basin. Pre-distribution parameters used as input to PRMS for step 3 are the post-calibration parameters in Step 2-Calibration Near-Native subbasins. Post-distribution model parameters include interpolated parameters from the calibrated near-native subbasins. Output files include daily PRMS simulated streamflow (seg_outflow) and observed streamflow (runoff) at five USGS streamgages along the mainstem Rio Grande. These PRMS model input and output data are intended to accompany a U.S. Geological Survey Scientific Investigations Report (Chavarria and others, 2020).