Pine Butte Fen 



Clinatic setting. The net annual precipitation balance for Pine 

 Butte fen (from the MAPS database) is -20 inches, at the humid end 

 of the range shown by Great Plains sites. Mean monthly 

 precipitation for the Blackleaf Canyon climatic station shows a 

 broad summertime peak with a June maximum. Total annual 

 precipitation records at the Blackleaf Canyon station are 

 incomplete for recent years; reported totals since 1990 were above 

 the long-term average for the station, with total precipitation in 

 1993 (the year of sampling) exceeding the long-term average by more 

 than 7 inches. 



Geologic setting. Pine Butte Fen occupies a broad area of ground- 

 water discharge from shallow aquifers recharged largely by seepage 

 from the channel of the Teton River. The unconsolidated aquifer 

 supporting the fen is composed of calcareous outwash and alluvivun 

 of late Pleistocene age, deposited near the terminus of an alpine 

 glacier flowing out of the Teton River canyon (nearby to the 

 northwest.) Reduced aquifer cross-sectional area and upward 

 potent iometric gradients drive ground-water discharge to the fen. 



The outwash gravel and other surficial sediments overlie shale, 

 siltstone and minor sandstone of the late Cretaceous-aged Two 

 Medicine and Telegraph Creek Formations. Cretaceous rocks are 

 believed to behave mainly as boundaries to ground-water flow 

 through surficial materials. 



Hydrologic type. Pine Butte Fen is an area of perennial ground- 

 water discharge from calcareous unconsolidated aquifers deposited 

 as outwash immediately beyond the local limits of alpine 

 glaciation. Surface water inflow from the small surface catchment 

 is a minor component of the fen water budget; ground-water 

 discharge supports perennial surface water outflow from the fen. 



Basin characteristics. Low topographic divides describe a surface 

 catchment only slightly larger than the fen itself; ground-water 

 supporting the fen originates as recharge outside the local surface 

 catchment. Most of the fen is vegetated; up-welling ground-water 

 maintains limited open-water pools of undescribed(?) depth. The 

 underlying aquifer narrows and probably thins to the southeast, 

 generating the ground-water discharge which supports the fen and 

 perennial outflow by two spring creeks to the North Fork of Willow 

 Creek. 



Water chemistry. Water sampled at WET60 is dilute, slightly 

 alkaline and calcium-bicarbonate in composition. Mineral 

 equilibria indicate oversaturation with carbonate phases. Trace 

 element concentrations generally are low; iron and zinc were 

 reported at intermediate concentrations and most other trace 

 element concentrations were below reporting limits. 



Chemical history. No other chemical data for WET60 were found. 



