The monthly streamflow distribution on four pairs of watersheds in southern Ontario was investigated. The dominant parent geological materials on the four pairs of watersheds were as follows: A, coarse-textured soils; B, moderately fine-textured soils formed on very fine sands and silts; C, medium-textured soils formed on till; D, fine-textured soils formed on till. The March–April runoff from the watersheds of fine-textured soils (D) was 56% of the annual runoff over a 9-year period, and from the watersheds of coarse-textured soils (A) it was only 34% of the annual runoff during the same time period. Larger amounts of groundwater recharge on watersheds of coarse-textured soils resulted in higher summer flows, more uniform seasonal flow, and reduced spring runoff extremes.The groundwater daily recession constant was likewise higher for the streams draining coarse-textured soils. The average estimated equivalent groundwater storage remaining when the monthly discharge was at a rate that was exceeded for 90% of the time, was as follows for the four geological classes: A, 0.267 in.; B, 0.090 in.; C, 0.035 in.; D, 0.007 in.