Daily estimates of baseflow derived from a non-linear, baseflow separation model. The files "baseflow_huc_01_02_03.csv", "baseflow_huc_04_05.csv", "baseflow_huc_06_07_08_09_10.csv", "baseflow_huc_11_12_13_14_15.csv", and "baseflow_huc_16_17_18_19_20_21.csv" have daily baseflow estimates for the period from water year 1981 to 2020 for 11,985 sites. The file "baseflow_rsqa.csv" has daily baseflow estimates for 462 sites that were sampled as part of the US Geological Survey Regional Stream Quality Assessment (RSQA). Values are only provided for days when water samples were collected. Missing values indicate gaps in the streamflow record.