the dominant conifer of the coastal forests in the Pacific 

 Northwest. 



A regionally endemic plant found within the lower Clark Fork 

 drainage is Cascade reedgrass ( Calamagrostis tweedyi ), a relative 

 of the more common pinegrass (Calam agrost is r ubescens ) . The 

 Montana Rare Plants Project lists this species as rare and the 

 U.S. Fish and Wildlife Service is considering it for federal 

 protection. Cascade reedgrass is found in meadows and open 

 coniferous forest near the headwaters of Cold Creek and Little Joe 

 Creek. 



Geologic Features 



About four percent of the Class I or Class II geologic sites 

 identified in the Montana Rivers Study were found in the lower 

 Clark Fork River drainage. 



Glacial Lake Missoula left its mark in this basin. Near the 

 Montana-Idaho border, lobes of the vast Cordilleran ice sheet from 

 British Columbia dammed the Clark Fork, creating water depths of 

 about 2,000 feet behind the dam. The glacial lake covered an area 

 of roughly 2,900 square miles and extended roughly 250 miles 

 upstream at least as far as Drummond and possibly as far as 

 Garrison. The ice dam is thought to have broken several times. In 

 Montana, the most impressive features associated with draining of 

 the lake are the giant ripple marks on the Flathead Indian 

 Reservation north of Perma -- although the Montana Rivers Study 

 did not look for features on reservations. 



Exposures of sediments deposited in the glacial lake also are 

 common in this drainage. These lacustrine deposits may be 20 or 

 more feet thick. Typically, the deposits include layered, light- 

 colored silts, clays, and fine sands. Occasionally, one may find 

 a much larger rock embedded in the fine sediments. These larger 

 rocks may have been floated out into the lake on an ice raft. As 

 the ice melted, the large rocks were deposited along with the 

 other finer lake sediments. The fine-grained sediments can be 

 viewed in many places in the basin, such as the Tarkio Flats area. 

 Along Interstate 90 these Lake Missoula sediments are well exposed 

 in a road cut on Cayuse Hill between Ninemile and Alberton. 



Paralleling the north side of the St. Regis River from Taft to 

 St. Regis is the Osborn Fault, a high-angle normal fault of late 

 Cenozoic age. Evidence of the fault consists of the scarplike 

 (cliff-like) mountain front and gullies or valleys segmenting the 

 scarp into triangular facets. In several areas near the fault 

 trace, mines were opened to extract silver and other precious 

 metals from adjacent mineralized areas. 



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