Upper Red Rock Lake 



Climatic setting. The net annual precipitation balance for Upper 

 Red Rock Lake is -5 inches, at the less evaporative extreme of the 

 range shown by sample sites of the intermontane valleys. Mean 

 monthly precipitation for the Lakeview climatic station shows 

 relatively even seasonal distribution with a maximum in June. 

 Annual precipitation totals for the Lakeview station shows an 

 apparent periodicity, with peaks in the 3-year running average 

 occurring every 5 to 7 years. During the late 1980s and early 

 1990s, the station recorded an unusually deep and extended period 

 of precipitation deficit with respect to the average for the period 

 of record. Precipitation during 1993 (the year of sampling) 

 exceeded the average by about 3 inches. 



Geologic setting. The WET71 site is underlain by lacustrine 

 deposits of undescribed thickness and character. Alluvial fan 

 deposits shed from the Centennial Mountain scarp immediately to the 

 south may interfinger with lacustrine deposits. Bedrock exposed 

 within the Upper Red Rock catchment includes a wide variety of 

 lithologies and ages; Paleozoic and Mesozoic-aged sediments 

 comprise much of the Centennial Mountains, while uplands to the 

 north of the lake expose large areas of Quaternary-aged volcanic 

 rocks . 



Major faults underlie the Centennial Valley and exert controls on 

 topography, sedimentation and ground-water flow. Geochemical and 

 thermal evidence indicate the discharge of deeply circulating 

 ground water into shallow aquifers north of the lake and into the 

 northern side of Upper Red Rock Lake itself. 



Hydrologic type. Upper Red Rock Lake is a natural structurally 

 controlled(?) basin modified by outlet controls designed to 

 stabilize lake water levels. The lake has surface water inflow and 

 outflow and also receives some ground-water inflow from a deeply 

 circulating geothermal system. 



Basin characteristics. Upper Red Rock Lake has a large high- 

 elevation catchment and a catchment to wetland area ratio which 

 ranks mid-range among intermontane valley sampling sites. Lake 

 depth and volume are not available. Diversions both for irrigation 

 (in the Alaska Basin upstream) and for fish and wildlife management 

 purposes occur within the catchment. 



Water chemistry. Upper Red Rock Lake at the WET71 sampling point 

 contains dilute, moderately alkaline calcium-bicarbonate water. 

 Mineral equilibria indicate slight over-saturation with carbonate 

 phases. Nitrate was reported at a concentration slightly above 

 reporting limits, while ammonium was below reporting limits. The 

 orthophosphate and total organic carbon concentrations ranked 

 toward the lower end of the range shown by sites in this class. 



