Shallow soil conductivity was mapped in the San Luis Valley, Colorado, using the DualEM421 electromagnetic sensor in March 2020. Data were acquired by towing the DualEM421 sensor on a wheeled cart behind an all-terrain vehicle, with the sensor at a height of 0.457 m above the ground surface. Approximately 62 line-kilometers of data were acquired over an area of nearly 1.5 square kilometers, with 20 m separation between survey lines. Data were manually edited for noise sources (powerlines, pipelines, or other buried structures), and averaged to regular output soundings every 1 m along survey lines. Data were corrected for offset between the recorded GPS location and data locations for each coil pair, but were not corrected for pitch and roll of the sensor. The processed data were inverted to recover models of electrical resistivity structure as a function of depth at each sounding location using a spatially constrained inversion. This data release contains the raw data, processed data, and inverted resistivity models. Digital data of the laterally constrained inversions are provided and fields are defined in the data dictionary. Model results show typical depth of investigation of about 4 – 6 m.