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Runoff processes in Mongolian drainage basins have received little study. The present work clarifies differences in runoff characteristics between granite (G-basin) and sandstone (S-basin) drainage basins near Ulaanbaatar. The drainage area of the G- and S-basins studied is 1.675 and 2.695 km2 and the maximum relief is 450 and 500 m, respectively. These hydrological measurements reveal clear differences in runoff characteristics. First, the constant small discharge in the G-basin implies that the dominant runoff process is infiltration into bedrock or weathered mantle and that only baseflow occurs; quickflow and through-flow are not dominant. Second, clear peak discharges and rapid response of discharge to rainfall in the S-basin implies that surface flow occurs. Finally, the slow recession rate after peak discharge suggests that through-flow is more significant in the S-basin than in the G-basin. [ABSTRACT FROM AUTHOR]