INTRODUCTION 



This report describes a sensitive species botanical survey 

 of Bureau of Land Management (BLM) holdings in the drainage of 

 Horse Prairie Creek. The study area lies in a high intermountain 

 basin in Beaverhead County, in southwestern Montana. The main 

 purpose of this work was to locate and survey populations of 

 sensitive and watch plant species as proposed by the BLM for 

 Montana (USDI Bureau of Land Management 1993) and prospective 

 sensitive and watch species currently tracked by the Montana 

 Natural Heritage Program (MTNHP) as plant species of special 

 concern (Heidel 1994). 



Surveys to determine the location and size of populations of 

 rare species are being conducted throughout the west in response 

 to the Endangered Species Act of 1973 and subsequent conservation 

 initiatives by the BLM and other agencies. These surveys 

 represent a botanical baseline to aid in identifying conservation 

 priorities and developing protection and compatible management 

 strategies. Area surveys have recently been conducted by MTNHP 

 on surrounding BLM lands in Beaverhead County in the Tendoy 

 Mountains and upper Big Sheep Creek drainage (Vanderhorst and 

 Lesica 1994), on Dutchman Mountain (Vanderhorst 1994a), and m 

 the vicinity of Lemhi Pass (Vanderhorst 1994b). 



THE STUDY AREA 



Horse Prairie Creek flows from its headwaters near Deadman 

 Pass on the Continental Divide to Clark Canyon Reservoir, where 

 it joins Red Rock Creek to form the Beaverhead River. The 

 designated study area included, in its western part, all BLM 

 lands in the upper drainage of Horse Prairie Creek, including its 

 tributaries, Bloody Dick and Trail Creeks. The eastern part of 

 the study area was designated as BLM lands within Townships 9 

 South and 10 South extending east to Interstate Highway 15. 

 Defined as such, the drainage of Medicine Lodge Creek was 

 excluded, and part of the upper drainage of the Beaverhead River 

 was included. Maps of the complete study area are included in 

 the results section (Figures 1 and 2) and in Appendix A. 



The study area lies mostly in the broad Horse Prairie Basin 

 and includes foothills of the surrounding Beaverhead, Pioneer, 

 and Tendoy ranges. The geology of most of the area is mapped as 

 Tertiary basin sediments and Quaternary alluvial deposits, but 

 smaller units of Tertiary volcanics and Paleozoic and Precambrian 

 sediments are also included (Ross et al. 1955, Geach 1972). The 

 Paleozoics lie in a belt to the north and south of Clark Canyon 

 Reservoir and include limestones of the Madison Group which 

 support a unique flora. The soils of the study area are broadly 

 mapped as aridisols, inceptisols, and mollisols with ustic-cryic 



