| Over 50% of the global stream network currently dries each year and drying is expected to increase. Climatic, land use and geologic controls on drying vary spatiotemporally, but geologic controls remain poorly understood because practical constraints limit subsurface data collection. I measured subsurface saturated hydraulic conductivity (Ksat), a key geological control on stream drying, throughout the ~16-km2 Gibson Jack Creek, Idaho. I characterized the spatial structure of Ksat along both Euclidean and hydrologic distances along the stream network based on 194 measurements following an unbalanced nested sampling design at 50-70cm below the channel surface. Ksat varied by ~1000x and was autocorrelated over single-meter distances; it was significantly higher in perennial than non-perennial reaches (p-value = 3e-6) and varied significantly with underlying lithologic or soil textural class (p-value = 0.001, 0.03), but not other landscape metrics. Thus, accurate predictions of fine-scale drying patterns may require detailed Ksat measurements. Keywords: Saturated hydraulic conductivity, subsurface controls, flow permanence, regulation, Clean Water Rule, intermittency, stream drying, intermittent streams, headwater stream networks, hydrology, Idaho |