Using data from alpine and subalpine watersheds in the southern and central Sierra Nevada, California, we develop the concept of representative elementary area (REA) for a hydrological variable (maximum snow depth at the beginning of the melt season), and for outflow concentrations and the annual export of a biologically important ion (nitrate) and the products of weathering (base cations and silica). Up to 1000 snow-depth measurements were taken each year since 1990 at maximum accumulation in the upper Marble Fork watershed (a 1900-ha headwater watershed of the Kaweah River, 36°36'22“N, 118°40'59”W). The random nature of snow distribution is illustrated in semivariograms, which usually have an autocorrelation range of <30 m, i.e., adjacent pixels with similar terrain and radiation inputs can have dissimilar snow depths. There is a consistent year-to-year relationship between the mean Marble Fork basin snow-depth at maximum accumulation and mean depths in the sub-basins; the REA appears to be on the order of 50 ha. Our results suggest that the REA for annual volume-weighted mean (VWM) nitrate concentration, nitrate yield, and possibly the temporal variation in outflow concentrations lies in the range of 35 to 70 ha. A similar-sized REA seems to apply to the annual export and VWM concentrations of base cations and silica.