| Summary: | An area of transition between mountain and continental glaciation in the western United States lies near the Boulder Mountains of Montana. A relatively low altitude ice mass called the Boulder Mountain ice cap, or BMIC, developed in the Boulder Mountains during the last glacial maximum, or LGM, in the Pleistocene Epoch about 17,000 year ago. The development of the BMIC has not been studied in this area since initial descriptions by Ruppel (1962), and limited new mapping by my mentor. Using Geographic Information Systems, or GIS, I have digitized Ruppel’s maps and portions of other maps. The digitized data were updated by field checking the pre-existing data and new mapping in areas of incomplete data. Mapping was carried out in the difficult terrain with the use of GPS units, topographic maps, and digitized versions of Ruppel’s map. In several areas ice boundaries were checked by identifying presence of glacial features including glacial sediment and debris at ice boundaries and striations on bedrock indicating ice movement. Upon returning from the field, the data underwent GIS analysis and spreadsheet modeling in collaboration with Ryan Bleess. These results helped determine a more accurate area and thickness of the BMIC. Results were then used to compute the equilibrium line altitudes, or ELAs, of the BMIC. Above the ELA the glacier is resistant to melting in all seasons. Our study determined lower ELA’s than those previously calculated in the area around the BMIC, suggesting a colder climate in this area during the LGM.
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