Downwind of Silicon Valley, flower-filled grasslands on nutrient-poor soils weathered from serpentinite support the threatened Bay checkerspot butterfly and numerous imperiled plant taxa. This biodiversity hotspot is at risk from exotic annual grasses that vigorously invade under elevated N-deposition, which was the primary nexus for the Santa Clara Valley Habitat Plan, a regional Habitat Conservation/Natural Communities Conservation Plan approved in 2013. Tracking local and regional N-deposition for this plan is a challenge. Starting in 2016, samples of late dry-season (Sep.-Oct.) baseflow from springs revealed highly elevated nitrate, up to 5.5 ppm NO₃-N, demonstrating high rates of leaching excess nitrate. Spatial patterns in 2016-2018 showed higher nitrate closer to urban Silicon Valley, and at low elevations closer to large highways and (often) below the inversion layer. In 2024, samples from 35 springs across a broader geographic range showed spatial gradients congruent with known pollution gradients and the elevation effect, allowing production of an interpolated map. Springs in the southwest part of the study area, outside the main pollution plume, have little or no nitrate. A 10-year time series (2016-2025) from 8 springs showed that the interannual ranges for sites were 0.3 to 1.1 ppm, compared with site means of 1.9 to 5.1 ppm. Much of that temporal variability could be explained by a positive effect of annual precipitation (Oct.- Sep., p = 0.001), with a residual downward trend of -0.016 ppm/year (p = 0.016). The hydrogeology of these springs indicates that the nitrate concentrations represent a 2-4 year average. Both TDEP and NO_x measurements in San Jose show downward trends over this period, but of greater proportional magnitude in TDEP (11%) than the nitrate data (3% on average). This method is simple and inexpensive - 1 or 2 days of sample collection followed with analysis by a local certified laboratory and it provides invaluable spatial and temporal data on integrated N-deposition.