This data set contains cross-section geometry and sediment-size distribution data collected in the fall of 2015 from Muddy Creek and North Fork Gunnison River below Paonia Reservoir, Colorado. Six cross-sections were surveyed using Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) methods to document channel geometry below the reservoir. One cross-section was surveyed on Muddy Creek below Paonia Reservoir, and five cross-sections were surveyed from North Fork Gunnison River below Paonia Reservoir. All six cross-sections are incorporated in this data release within one shapefile. Pebble-counts were performed at each of the six cross-sections to document sediment-size distributions downstream from the reservoir. Four transects were located in the vicinity of each cross-section, where sediment size was measured and recorded. Transect locations were based on bankfull channel width; with transect 1 located one bankfull channel width upstream from the surveyed cross-section, transect 2 at the surveyed cross-section, and transects 3 and 4 located one and two bankfull channel widths downstream from the surveyed cross-section, respectively. All of the sediment-size distribution data are presented in .CSV files, with one file for each cross-section location incorporating all of the data for each of the four transects at that location.