In recent decades, the Rocky Mountain West has been one of the fastest growing regions in the United States. Headwater streams in mountain environments may be particularly susceptible to nitrogen enrichment from residential and resort development. We utilized stream water chemistry from six synoptic sampling campaigns combined with land use/land cover (LULC) and terrain analysis in geostatistical modeling to examine the spatial and seasonal variability of LULC impacts on stream water nitrate. Stream water nitrate was spatially correlated for longer distances during the dormant season than during the growing season, suggesting the importance of biological retention. Spatial linear models indicated that anthropogenic sources best predicted stream water nitrate in the dormant season, while variables describing biological processing were the best predictors in the growing season. This work demonstrates the importance of (1) incorporating spatial relationships into water quality modeling and (2) investigating stream water chemistry across seasons to gain a more complete understanding of development impacts on stream water quality.