John Smart Photo(Taken from the Final Sweet Grass Hills Amendment and Environmental Impact Statement, April, 1996)
The Sweet Grass Hills provide for unique and limited soils developed on igneous bedrock in mountainous and forested areas.
John Smart PhotoThe East Butte area is steep and dissected by deep drainages. Most of the Butte (about 80%) is on slopes greater than 25 percent, with most slopes between 40 and 60 percent. Elevations range from 5,100 to about 6,400 feet.
The area is dominated by steep and very steep barren areas with more than 90 percent of the surface occupied by stones and boulders of igneous (syenite) origin. These igneous scree or talus areas are virtually free of vegetation except for lichens. Elve, very cobbly loam soils on North slopes produce forest vegetation with a limited grassed understory and are adjacent to and within the talus slopes. These deep, excessively well-drained, cobbly soils have 35 to 60 percent rock fragments by volume. The water erosion hazard, when bare, is high due to steep slopes, and excessive cobbles and stones.
Adjacent to the igneous laccolith material are the shallow Winspect cobbly loam and moderately deep, Winspect, cool phase cobbly loam soils over limestone on ridges and convex slopes associated with the limestone bedrock outcrops. This soil produces sparse grass and forest vegetation of lesser quality.
The surrounding footslopes below East Butte are dominated by Roy and Barkof clay soils formed on sedimentary clay shales. These deep, well-drained soils have a high risk to water erosion, due to slopes and clay texture. The surrounding glacial till plain is represented by Vida-Williams-Bearpaw soils formed in glacial till. These deep, well-drained clayey soils have erosion hazard to both water and wind, when bare. These soils are easily compacted when moist.
John Smart PhotoThe Middle Butte area is steep and dissected by deep drainages. Most of the land is on slopes greater than 25 percent, with most slopes between 40 and 70 percent. Elevations range from 5,100 to about 6,400 feet.
The area is dominated by steep and very steep barren areas with more than 90 percent of the surface occupied by igneous (syenite) stones and boulders. These igneous scree or talus areas are virtually free of vegetation except for lichens. Most of the Middle Butte area is occupied by Perma and Whitlash cobbly loam soils on the 25 to 70 percent slopes which produce limited grass and shrub vegetation and are adjacent to and within the talus slopes. Perma cobbly loam soils are deep, somewhat excessively well-drained, and have 35 to 60 percent cobbles and stones by volume. The water erosion hazard, when bare, is high due to steep slopes, and excessive cobbles and stones. Whitlash cobbly loam soils are shallow, well-drained soils over shattered igneous bedrock, have 35 to 60 percent cobbles and stones by volume. The water erosion hazard, when bare, is high due to steep slopes, and excessive cobbles and stones. The large adjacent areas on the 8 to 25 percent slopes are dominated by the Perma gravelly loam soils.
The surrounding footslopes below Middle Butte are dominated by Roy and Barkof clay soils formed on sedimentary clay shales. These deep, well-drained soils have a high risk to water erosion, due to slopes and clay texture. The surrounding glacial till plain is represented by Zahil-Zahl soils formed in glacial till. These deep, well-drained clayey soils have erosion hazard to both water and wind, when bare. These soils are easily compacted when moist.
The West Butte area is steep and dissected by deep drainages. Most of the land is on slopes greater than 25 percent, with most slopes between 40 and 70 percent. Elevations range from 5,100 to about 6,400 feet.
The area is dominated by steep and very steep barren areas with a large percentage of the surface occupied by igneous (syenite) stones and boulders. These igneous scree or talus areas are virtually free of vegetation except for lichens. Areas of Stemple soils on north facing slopes produce forest vegetation with a limited grass understory. Stemple soils are very deep, well-drained, have 35 to 60 percent cobbles and stones by volume. The erosion hazard, when bare, is high due to steep slopes and excessive cobbles and stones. Most of the West Butte area is occupied by Perma and Whitlash cobbly loam soils on the 25 to 70 percent slopes which produce limited grass and shrub vegetation, are adjacent to and within the talus slopes. Perma soils are deep, somewhat excessively well-drained, and have 35 to 60 percent cobbles and stones by volume. The water erosion hazard, when bare, is high due to steep slopes, and excessive cobbles and stones. Whitlash soils are shallow, well-drained soils over shattered igneous bedrock, have 35 to 60 percent cobbles and stones by volume. The water erosion hazard, when bare, is high due to steep slopes, and excessive cobbles and stones. Adjacent areas on the 8 to 25 percent slopes are dominated by the Perma soils.
The surrounding glacial till plain below West Butte are dominated by Vida-Williams-Bearpaw-zahl soils formed in glacial till. These deep, well-drained clayey soils have a high risk to water erosion, due to slopes and clay texture. These soils also have a soil blowing hazard from wind, when bare. These soils are easily compacted when moist.