We are interested in incorporating the effects of soils on streamflow generation in mountainous terrain into a water supply model. Our study site is a small headwater watershed in the Owyhee Mountains of southern Idaho. Two critical issues that must be addressed are the high degree of spatial variability of soil water content and the characterization of the lower boundary. In terms of spatial variability of soil water, extensive surveys using time domain reflectometry and neutron probe in combination with aerial photography have shown that: (i) a large amount of the spatial variability is strongly correlated with vegetation and soil type and (ii) there is a strong degree of temporal stability. These results provide a basis for capturing a large amount of the spatial variability while integrating the overall seasonal dynamics throughout the watershed. In terms of the lower boundary condition, shallow soils are common within the watershed but there is little evidence that the rock imposes a water flow restriction. In fact, streamflow appears to be highly responsive to inputs. Soil dielectric sensors profiles have shown that the vertical transmission of water is very rapid. Electromagnetic induction surveys have revealed likely high conductivity subsurface zones that may be responsible for transmitting water inputs that are removed from the stream. Recent groundwater data have confirmed that the subsurface, below the soils, is in fact, very highly conductive. These data illustrate the synergistic effect of combining different types of data to better understand and model watershed dynamics.