Reliability of ephemeral montane springs in Mojave National Preserve, California

Small springs in mountainous areas provide the only source of water for numerous wildlife species over a broad expanse of the Mojave Desert. A comprehensive inventory and annual surveys over nine years indicated that many such springs occur in canyons and ravines along the slopes and near the base of mountain ranges associated with small, locally recharged, perched aquifers and are drought ephemeral. Within the 643,112 ha study area 135 spring systems consisting of 238 distinct surface water expressions were monitored. Reliability of available surface water was correlated with watershed catchment area and spring brook length. Geologic field mapping of a subset of 39 springs indicated that the area of colluvial sediment above barriers was correlated with persistence of surface water from year to year, but the area of phreatophyte vegetation supported by spring discharge and hydraulic conductivity of the sediment surface were not. Reliable spring discharge through several years of sustained drought depends upon sufficient groundwater storage. Watershed catchment area, spring brook length, and area of colluvial sediment appear to be predictors of discharge persistence during drought for certain types of montane springs.