PROJECT AREA AND SAMPLING SITES 



The project area is located in Fergus County near the city 

 of Lewistown in central Montana. Big Springs, a few miles 

 southeast of Lewistown, is the source of Big Spring Creek and 

 generates most of its streamflow. Major tributaries of Big 

 Spring Creek, including Casino Creek, head on the north flanks of 

 the Big Snowy Mountains, an outlier of the Middle Rockies 

 Ecoregion. Study sites are located in the Montana Valley and 

 Foothill Prairies Ecoregion (Omernik and Gallant 1987) . 



The surface geology of the Big Snowy Mountains consists of 

 limestones and dolomites of Paleozoic age (Taylor and Ashley, 

 undated) . Lower in the watershed, where the study sites are 

 located. Cretaceous shales of the Colorado Group are exposed 

 (Taylor and Ashley, undated) . 



Natural vegegation in the study area is mixed grassland 

 dominated by rough fescue, Idaho fescue, and bluebunch wheatgrass 

 (USDA 1976) . The main land uses in the Big Spring Creek 

 watershed are agriculture, recreation, and urban development. 



Periphyton samples were collected at one site on Casino 

 Creek and 3 sites on Big Spring Creek (Table 1) . One sample was 

 collected from Big Spring' Creek just above Casino Creek and two 

 samples were collected at a distance of 1 mile and several miles 

 below Casino Creek. Only one sample was collected from Casino 

 Creek- -below the spill - -because of problems with access (Carol 

 Endicott, MDEQ, personal communication) . 



Elevations at the sampling sites range from about 4,000 feet 

 at the sites above Lewi'stown to about 3,900 feet at the lowest 

 site on Big Spring Creek below Lewistown. Casino Creek and the 

 upper 2 sites on Big Spring Creek are classified B-1 in the 

 Montana Surface Water Quality Standards,- Big Spring Creek below . 



