This dataset contains cross-section geometry and sediment-size distribution data collected in the fall of 2018 from Muddy Creek and North Fork Gunnison River below Paonia Reservoir, western Colorado. Six cross-sections were surveyed using Real-Time Kinematic Global Navigation Satellite System (RTK-GNSS) methods to document channel geometry below the reservoir in 2015. Those same cross-sections were re-surveyed using the same methods in 2018 to document any changes. 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. 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.