13 



Rivers. One of the two Madison River occurrences is based 

 on a collection in 1899. 



J. Occurrences in the study area: One population was 



previously known from foothills above the Beaverhead River 

 just north of Pipe Organ Rock (002). This occurrence was 

 relocated and resurveyed in 1994, revising population 

 boundaries and adding new subpopulations . Much of the 

 population is not on BLM land. An Element Occurrence Record 

 and map showing the precise location are included in 

 Appendix C. 



HABITAT 



L. Associated vegetation: Astragalus terminalis grows in 

 grasslands, sagebrush/grasslands, and in stony and rocky 

 habitats (Barneby 1964, and Montana records). The 

 occurrence in the study area is in grasslands dominated by 

 bluebunch wheatgrass (Elymus spicatus) and needle and thread 

 (Stipa comata) , without or with sagebrush (Artemisia 

 tridentata and Artemisia tripartita) . Additional associates 

 at the site include Arenaria kingii, Astragalus adsurgens , 

 Astragalus drummundii , Astragalus miser, Castilleja 

 pallescens , Koeleria macrantha, and on south-facing slopes, 

 Opuntia polyacantha. The lower slopes of the main 

 population area are being invaded by weeds, most notably 

 sweetclover (Melilotus officinalis) and cheatgrass (Bromus 

 tectorum) . A photographic slide of the habitat is attached 

 at the end of this report. 



!. Topography: Railhead milkvetch grows on hillsides, 



ridgecrests, and river benches (Barneby 1964 and Montana 

 records). The occurrence in the study area is on steep 

 hills above the river bottom at around 5,600 feet. The 

 population is in lower slope positions with both northerly 

 and southerly aspects. 



I. Soil relations: The soils are usually derived from 



calcareous parent materials (Barneby 1964). The soil at the 

 site in the study area is stony and probably derived from 

 alluvium, but possibly downhill from a limestone outcrop. 

 The soil is extremely well drained and was dry by the survey 

 date (June 21 ) . 



POPULATION DEMOGRAPHY AND BIOLOGY 



L. Demographic details: The population in the study area was 

 originally (1983) estimated to consist of fewer than 50 

 plants confined to a small area, but, in 1994, additional 

 subpopulations were located on adjacent private land 

 (thought to be BLM at the survey date) and the total numbers 

 were estimated at 1,000-2,000, covering at least 40 acres. 



