The U.S. Geological Survey (USGS) as part of the Department of Interior WaterSmart Program compiled published estimates of groundwater discharge to streams in the Upper Colorado River Basin into a dataset and developed a geospatial database. For the purpose of this compilation, groundwater discharge to streams consists of base-flow, and may include contributions from groundwater discharge from various flow paths, lateral seepage, hyporheic flow, and irrigation return flow. Stream reaches from the National Hydrography Dataset (NHD) where there was groundwater discharge estimates were delineated in the geospatial database. Attributes describing the methods used for estimating groundwater discharge were created. Feature class attributes associated with each stream reach include: groundwater discharge (acre-ft/yr), method of measurement, report reference, defined reach, base flow index estimate (acre-ft/yr), and 8-digit HUC(s) (hydrologic unit code(s) for the reach). In addition, groundwater discharge estimates were calculated using attributes from a flow characteristics dataset (Wolock, 2003), the average annual base-flow index (BFI) value and the average daily streamflow value. The calculated groundwater discharge estimates were included in the database as separate attributes and were compared to reported estimates of groundwater discharge. Groundwater discharge estimates calculated using BFI were greater than reported groundwater discharge estimates. References cited: Wolock, D., 2003, Flow Characteristics at U.S. Geological Survey Streamgages in the Conterminous United States: U.S. Geological Survey Open-File Report 2003-146, accessed July 2, 2012 at https://water.usgs.gov/GIS/metadata/usgswrd/XML/qsitesdd.xml