STUDY AREA AND METHODS 



The study area is in the Beaverhead Section ecological unit of the U.S. Forest Service 

 Northern Region (Nesser et al. 1997). This section has a cold continental climate characterized 

 by a warm, dry summer and a cold, dry winter; mean annual precipitation ranges from 9-20 

 inches (23-51 cm), with about 10% falling as snow. Large gravel filled valleys, surrounded by 

 steep fault block mountains of a variety of bedrock types, dominate the topography. Valley 

 elevation ranges from 4700-7600 feet, potential natural vegetation is largely sagebrush-steppe. 

 The majority of mines surveyed were in this Southwest Montana Intermontane Basins and 

 Valleys subsection. 



Lists and location of mine sites and workings to be visited were obtained from the Dillon 

 and Headwaters Resource Areas - BLM (= Dillon and Butte Field Offices, respectively), from 

 databases developed by the Montana Bureau of Mines and Geology, and directly from 

 topographic maps. Areas of focus tended to be at and near mines on the BLM lists, and 

 particularly in mining districts (Ermont, Rochester, Tidal Wave) scheduled first for mine 

 reclamation activities. The majority of mine workings surveyed were located in southwestern 

 Montana, in Beaverhead and Madison counties, with a handful of sites in extreme southern 

 Silver Bow County. 



Precise location of 52 sites was recorded on a differentially-correctable Trimble 

 Geoexplorer II GPS unit, but some sites were never recorded and some files were inadvertently 

 lost. Thus the record of GPS locations in Table 1 is incomplete because of missing data, and the 

 production of maps from the available data seemed pointless. Nevertheless, all mines surveyed 

 were recorded to quarter-quarter section precision (see Table 1 ), and photographs, where taken, 

 were filed for future reference with original field data sheets at the Montana Natural Heritage 

 Program Helena office. 



Mine workings represent a continuum of types, but were classified into three basic 

 categories: adits (horizontal slender workings), shafts (vertical slender workings), and pits 

 (vertical broad workings). Some workings fell somewhere between adits and shafts, and are 

 more accurately termed "inclines"; inclines usually appear on topographic maps (if portrayed at 

 all) as shafts. Most often, inclined workings were angled > 30°, and contained remains of 

 ladders in the main passage to aid movement. In this report inclined workings steep enough for 

 ladders to be helpful are categorized as shafts and those of lesser angle are termed adits, for 

 reasons of simplicity and lack of clear criteria for demarcation between adits, inclines, and 

 shafts. 



For each mine site visited, the presence or absence of open portals was the first variable 

 noted. If a mine working had not collapsed, then the dimensions of each opening were measured 

 or estimated, any obstructions (grating, cable netting, fallen timbers or rock, etc.) noted, and if 

 accessible the entrance was inspected for bat spoor (primarily droppings). Temperature of 

 outward air flow, if present, was also measured. Dominant cover-type of the surrounding habitat 

 at mines was classified following a standardized scheme used by Montana Partners-In-Flight for 

 point-count monitoring of birds (Hutto and Young 1999). 



A small subset of mine workings was examined internally for bats and to install 

 electronic data loggers (HOBO; Onset Computer Corporation, Bourne, MA) Data loggers were 

 set to record mine air temperature and relative humidity every 6 h, put in the selected mines in 

 September 1998, and left in situ during winter 1998-1999. The underground climate data 

 captured by the data loggers are not available for this report. Underground workings were 



