The sedimentary rocks of the Pasco Basin include glaciofluviatile deposits and the Ringold Formation. They may also include sedimentary rocks interbedded with the basalts. In terms of the ground-water flow continuum these rocks are divided into the unsaturated zone, the upper dominantly coarse-clastic part of the zone of saturation and the lower dominantly fine-grained part of the zone of saturation. The effective porosity of the glaciofluviatile deposits that make up the upper coarse-clastic zone is no more than 3 or 4 percent. The effective porosity of the Ringold coarse clastics and fine clastics of the lower part has not been adequately measured--but is undoubtedly smaller. Drillers' logs combined with pumping tests were used as shown on this report to estimate and map the transmissivity and mean hydraulic conductivity of the saturated sedimentary rocks. They show that the largest values of transmissivity and mean hydraulic conductivity in the unconfined aquifer occur where the saturated thickness of the Pasco Gravels is largest. Intermediate values occur where the Pasco Gravels are thinnest and the Middle Ringold Conglomerates are thick. Low values occur where the Middle Ringold Conglomerate is thin, the Pasco Gravels are non-existent, and the Lower Ringold makes up the bulk ofmore » the saturated section.« less