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t, J iz ROCK CREEK SIZE: approx. 1500 acres within the RFETS C.OCATION: Louisville Quadrangle (3910582) T2S, R69W, Sects: 2,3,4,9,10 BIODIVER.STTY RANK: B3 PROTECTION URGENCY: Pl MANAGEMENT URGENCY: M2 C:ENERAL DESCRIPTION: The Rock Creek Site occurs on the northern edge of the F:ocky Flats alluvial mesa. Near the line separating Boulder and Jefferson counties, the site is approximately 2-3 miles east of the foothills and on the far western edge of the Great Plains. The flora is the typical natural flora of the surrounding mesas and grasslands. Most of the site was part of a livestock ranch (The Lindsay Ranch) before rze property was purchased by DOE in 1974. The fauna is greatly changed from prehistoric periods with the losses or reduced populations of most of the large herbivores (e.g. bison, bighorn sheep, pronghorn and ells) and losses of the major carnivores (wolves) and omnivores (grizzly and black bears). The Rock Creek Site is bounded on the north by State Road 128, on the west by State Road 93 and on the south and east by other portions of the Rocky Flats Environmental Technology Site. Numerous roads, diversion ditches, and gravel mines are found within or adjacent to the site. Boulder City Open Space adjoins the site to [he north of State Road 128. i\fATURAL HERITAGE RESOURCE SIGNIFICANCE: When the first pioneers came to the region, grasslands extended easi<vard from the base of the mountains for hundreds of miles (Mutel and Emerick 1984). Herds of pronghorn and bison were hunted by gray wolves and Indians. Today much of the natural vegetation has been replaced by croplands, cattle pastures, and human developments. Along the Front Range, extensive urbanization has dramatically changed the character of the grasslands. Due to the great loss of grasslands throughout the United States we feel special effort should.be made to maintain any remaining significant grasslands. The Rock Creek area was found to have remnants of good quality grasslands. However, signs of disturbance and potential tltreats abound and the integrity of the area is considered highly threatened. The Rock Creek Site contains a good example of a xeric tallgrass prairie community v<•ith a rich grass flora, a Great Plains riparian ecosystem supporting a population (or subpopulation) of Preble's meadow jumping mouse and several unusual plant communities associated with seeps. The dominant species on the xeric grassland (xeric tallgrass prairie - AndronoQOn g=rardii-Schizachyrium scoparium fAndropoQOn scopariusl. Bourgeron and Engelking 1994) are big and little bluestem (Andro~gon eg rardu and A. scoparius), but other .-.fin-~.. .. ..•m~.~ -.~IfTT!^nT~R.. .. .~. .:r.. .. ...~ '. -. ~. .:.._ .-- .. _: _... .. n i f>: ~. ..-T- S'/-'9~