Warhorse National Wildlife Refuge 



Climatic setting. The net annual precipitation balance for 

 Warhorse Lake (from the MAPS database) is -28 inches, placing 

 Warhorse in the middle of the narrow range of evaporative intensity 

 shown by sites of the unglaciated plains, and near the evaporative 

 extreme of the range shown by the entire data set. Mean monthly 

 precipitation for the Winnett climatic station shows a pronounced 

 summer peak with a June maximum. Annual total precipitation for 

 the Winnett station is not available for recent years; regionally, 

 many stations experienced above-average precipitation in 1993 (the 

 year of sampling) and near-average precipitation in 1992. 



Geologic setting. Warhorse Lake and it's natural catchment are 

 underlain entirely by fine-grained sedimentary rocks of the 

 Colorado Group. Colorado Group shales in the Warhorse area are 

 described as bearing ubiquitous selenite (gypsum). The Warhorse 

 basin appears to be structurally controlled, lying along the axis 

 of a northwest-trending syncline. No description of surficial 

 sediments in the immediate area is available; based on the 

 underlying geology, surficial sediments are inferred to be mainly 

 fine-grained, of low permeability and gypsiferous. 



Hydrologic type. Warhorse Lake occupies a natural, structurally 

 controlled basin augmented by impoundments and formerly supplied 

 by water imports from Fords Creek, draining portions of the 

 southern Judith Mountains. Water imports have not occurred for at 

 least 10 years, and water supply to the lake is now derived only 

 from the natural surface catchment. Warhorse Lake has presently 

 unused outflow structure formerly used to control irrigation water 

 supply. 



Basin characteristics. The natural catchment of Warhorse Lake is 

 relatively small, and the catchment to wetland area ratio is the 

 lowest among sites of the unglaciated plains. Past water imports 

 from the Fords Creek drainage (no longer practiced) effectively 

 increased the contributing area many-fold. Information on water 

 depth is not available. Under current management practices, the 

 lake is reported to hold water during the autumn bird migration 

 less than 50% of the time, and low basin gradients ensure a high 

 degree of shoreline transience. 



Water chemistry. At the time of sampling, Warhorse Lake contained 

 slightly alkaline, "oligosaline" water of unusual calcium-sulf ate 

 composition. [Calcium is the proportionately highest cation but 

 does not dominate the cation field, accounting for 42% of the 

 cation equivalence.] Equilibrium calculations indicate near- 

 equilibrium with carbonate phases and undersaturation with gypsum. 

 The major-ion chemistry of Warhorse Lake is apparently influenced 

 by the (reportedly) ubiquitous occurrence of selenite (gypsum) in 

 local Colorado Group shales and derivative soils. 



