This metadata record describes the observed and estimated hydrologic metrics for the 1980 to 2019 period for U.S. Geological Survey streamgage locations across the Conterminous United States. The datasets are arranged in four files: (1) CONUS_Observed_Estimated_HMs_Annual_Monthly.csv, (2) CONUS_Bootstrap_Validations_for_Models.csv, (3) CONUS_Streamflow_Gages_for_Models.csv, and (4) Data_Dictionary_Flow_Metrics.csv. The CONUS_Observed_Estimated_HMs_Annual_Monthly.csv file contains the following six attributes: (1) the U.S. Geological Survey streamgage identification number, (2) calendar year, (3) observed hydrologic metric, (4) estimated hydrologic metric, (5) hydrologic metric abbreviation, and (6) aggregated level 2 ecoregion. The observed hydrologic metrics were calculated using collected streamflow daily values from U.S. Geological Survey streamflow gaging stations (U.S. Geological Survey National Water Information System, http://dx.doi.org/10.5066/F7P55KJN), and the estimated hydrologic metrics were estimated by cross-sectional time series random forest modeling methods by Miller, M.P., Carlisle, D.M., Wolock, D.M., and Wieczorek, M., 2018, A database of natural monthly streamflow estimates from 1950 to 2015 for the conterminous United States: Journal of the American Water Resources Association, 54(6), 1258-1269 [Also available at https://doi.org/10.1111/1752-1688.12685]. Forty-seven hydrologic metrics representing magnitude, frequency, duration, and timing were calculated. The hydrologic metric abbreviations, definitions, units, and citations are detailed in the Data_Dictionary_Flow_Metrics.csv file. The low- and high-flow magnitudes were calculated from the 10th and 90th percentile non-exceedence streamflows divided by the drainage area, respectively. The low- and high-flow frequencies were calculated as the number of pulses below the 10th and above the 90th percentile values, respectively. The low- and high-flow durations were calculated from the length of time (in days) that the streamflow was below the 10th percentile or above the 90th percentile, respectively. The low- and high-flow seasonality values were calculated based on frequency of occurrence in different seasons (for more details, please see Eng, K., Carlisle, D.M., Grantham, T.E., Wolock, D.M., and Eng, R.L., 2019, Severity and extent of alterations to natural streamflow regimes based on hydrologic metrics in the conterminous United States, 1980-2014: U.S. Geological Survey Scientific Investigations Report 2019-5001, 25 p. [Also available at https://doi.org/10.3133/sir20195001]. The CONUS_Streamflow_Gages_for_Models.csv file contains the U.S. Geological Survey list of streamflow gaging stations used in cross-sectional time series random forest models. The CONUS_Bootstrap_Validations_for_Models.csv file lists the U.S. Geological Survey streamflow gaging stations used in the bootstrapped validation data sets used to assess model performance. In addition, bootstrap validation also assesses model robustness by testing various calibration configurations. These bootstrap validation data sets may contain random amounts of observations that are outside the range of the observations used in the calibration, and/or observations that are not independent from one another. There are no missing values in any of the files. The three data files are in a comma separated value text format.