The unit‐source watershed is an intermediate step between plots, in which certain runoff generative processes can be isolated, and large watersheds, the yields of which are controlled by the hydraulics of their complex channel systems. Several unit‐source watersheds have been instrumented within the Walnut Gulch experimental watershed in southeastern Arizona. Their comparative data indicate some basic hydrologic relationships between net runoff and size of drainage area, the significance of storm patterns, the relation of runoff and sediment yield to vegetational cover, and hydrograph characteristics.