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i ~ _. <br />14 <br />approach, we will assume (because of the scarcity of information) that it is somewhat <br />rare. This will allow us to prioritize information collection regarding this community. <br />We suspect that this, as with other foothills and western Great Plains communities, is <br />highly impacted throughout its range. <br />Vegetation communities associated with seeps are in some cases similar to other <br />wetlands at the site supporting sedges, rushes, and cattails (U. S. Army Corps of <br />Engineers 1994), and in some cases very different, supposing an unusual mixture of <br />shrubs including hawthorn (Crataegus ervthropoda), chokecherry (Prunus virQirtiana), <br />and snowberry (Symphoricarpos occidentalis). This shrub community is unusual and <br />may be restricted to the local area. <br />A unique shrubland community associated with the seeps at the Site is tentatively <br />classified as CrataeQUS erythrovoda-Prunus virginiana-Prunus americana seep shrubland. <br />This plant association is ranked GU/SU by the Natural Heritage Network indicating its <br />poorly known status. This plant association is similar to one described in Montana but <br />Crataegus ervthropoda is the dominant species in the Colorado community and <br />Crataegus succulenta is the dominant species in the Montana community (Hansen et <br />al. 1991). These small patches of shrublands are scattered throughout the Rock Creek <br />drainage where seeps form ar the contact of the relatively permeable Rocky Flats <br />Alluvium and the less permeable Arapahoe Formation. This community is not well <br />documented in the literature. Special effort should be undertaken to protect and to <br />be[ter understand the biodiversiry sigrtificance of this corrtmuniry. <br />Other portions of the Rock Creek Site are occupied by the shortgrass prairie plant <br />association, AQro~yron smithii-Bouteloua acilis (U. S. Department of Energy 1994a). <br />This plant association is believed to remain common, but is also highly impacted <br />throughout its range. The season of study for CNHP was not appropriate to assess the <br />ecological status of this plant association. Follow-up work will occur in the field season <br />of 1995. <br />The Preble's meadowjumping mouse (Zaous hudsonius ~reblei) occurs only in Colorado <br />and Wyoming. The mouse is known from Colorado on the basis of fewer than SO <br />specimens from Latimer, Weld, Boulder, Jefferson, Denver, Adams, and Arapahoe <br />counties (Armstrong 1972). Judging from its limited ecological and geographic <br />distribution in Colorado, the mouse probably is a Pleistocene relict, perhaps once <br />widespread in a tallgrass prairie across the eastern plains, but now restricted to <br />scattered localities on the Colorado Piedmont (Fitzgerald et al. in press). <br />Preble's meadow jumping mouse may be one of North America's rarest mammals. This <br />subspecies is isolated from its nearest relatives and was naturally rare (relatively) due <br />to its restricted habitat. The Preble's meadow jumping mouse habitat appears to be <br />restricted to relatively short distances from the riparian vegetation (Fred Harrington - <br />personal communication; C. A. Pagve -personal observation). <br />