The data are from soil salinity surveys conducted on California irrigated farmland between 1991 and 2017. The data consist of: (i.) geolocated field survey measurements of bulk soil electrical conductivity (ECa) and (ii.) laboratory determinations of soil salinity (ECe) and saturation percentage (SP) made on soil core sections extracted from the surveyed fields. The data comprise 277,624 ECa measurements and 8,575 ECe and SP determinations.