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Horse Rock Ridge Research Natural AreaEugene District , BLMWest Cascades, Oregon EcoregionCell(s):
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Access by gravel surface road. The access road is gated and locked.
The 153 ha Horse Rock Ridge RNA protects the best remaining grassy bald on the western margin of the Cascade Range. The RNA lies in the Coburg Hills at the eastern edge of the Willamette Valley southeast of Brownsville, Linn County, Oregon. The rugged topography, with rock outcroppings and steep slopes, formed over basalt and basaltic andesite of the Little Butte Volcanic Series deposited during the Oligocene and Miocene. A prominent basalt dike extends from the ridge top southeast down the slope. Elevation ranges from 488 to 872 m. Soils are Kinney cobbly loam and a rock outcrop/orthent complex. About two-thirds of the area has a southern exposure and the remainder lies on a north slope. Cool, wet winters and warm, dry summers characterize the maritime climate, with 127 cm of annual precipitation, most of which falls as rain between November and April. Vegetation on Horse Rock Ridge consists of open grasslands, old growth forest, and conifer reproduction on areas previously logged. The RNA contains 230 species of vascular plants. The grass bald, which covers 34 ha and contains several seeps, contributes most of the species diversity. The forest is dominated by Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla). The transition between the forest and grassland is dominated by hairy manzanita (Arctostaphylos columbiana), poison oak (Toxicodendron diversilobum), oceanspray (Holodiscus discolor), and serviceberry (Amelanchier alnifolia). Grazing may have begun as early as the mid-1800s, when the Willamette Valley was settled and possibly continued into the early decades of the twentieth century. All of the surrounding forest as well as some inside the RNA has been logged. The 1962 Columbus Day storm caused extensive blowdown and some of the trees on the gentler slopes were salvaged. A locked gate blocks the road to a radio tower located at the highest point in the RNA and rock berms have been constructed across old logging roads to prevent ORV and bicycle damage to the meadow. The area is used by hikers, botany students, and hunters. In 2000 the Eugene BLM established transects to monitor long-term vegetation changes in the grassland and forested areas. A study in the forested area uses lichens to monitor air quality. In 2004, a description of the RNA was published in Kalmiopsis, the journal of the Native Plant Society of Oregon.| Home | About RNAs | Interagency Program | Research Use | RNA Sites | Bibliography | Links |