Natural Resources
Conservation Service
Ecological site FX052X01X010
Dense Clay (DC) Dry Grassland
Last updated: 12/28/2022
Accessed: 11/23/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 052X–Brown Glaciated Plains
The Brown Glaciated Plains, MLRA 52, is an expansive and agriculturally and ecologically significant area. It consists of around 14.5 million acres and stretches across 350 miles from east to west, encompassing portions of 15 counties in north-central Montana. This region represents the southwestern limit of the Laurentide Ice Sheet and is considered to be the driest and westernmost area within the vast network of glacially derived prairie pothole landforms of the northern Great Plains. Elevation ranges from 2,000 feet (610 meters) to 4,600 feet (1,400 meters).
Soils are primarily Mollisols, but Entisols, Inceptisols, Alfisols and Vertisols are also common. Till from continental glaciation is the predominant parent material, but alluvium and bedrock are also common. Till deposits are typically less than 50 feet thick, and in some areas glacially deformed bedrock occurs at or near the soil surface (Soller, 2001). Underlying the till is sedimentary bedrock largely consisting of Cretaceous shale, sandstone, and mudstone (Vuke et al., 2007). Bedrock is commonly exposed on hillslopes, particularly along drainageways. Significant alluvial deposits occur along glacial outwash channels and major drainages, including portions of the Missouri, Teton, Marias, Milk, and Frenchman Rivers. Large glacial lakes, particularly in the western half of the MLRA, deposited clayey and silty lacustrine sediments (Fullerton et al., 2013).
Much of the western portion of this MLRA was glaciated towards the end of the Wisconsin age, and the maximum glacial extent occurred approximately 20,000 years ago (Fullerton et al., 2004). The result is a geologically young landscape that is predominantly a level till plain interspersed with lake plains and dominated by soils in the Mollisol and Vertisol orders. These soils are very productive and generally are well suited to dryland farming. Much of this area is aridic-ustic. Crop-fallow dryland wheat farming is the predominant land use. Areas of rangeland typically are on steep hillslopes along drainages.
The rangeland, much of which is native mixed grass prairie, increases in abundance in the eastern half of the MLRA. The Wisconsin-age till in the north-central part of this area typically formed large disintegration moraines with steep slopes and numerous poorly drained potholes. A large portion of Wisconsin-age till occurring on the type of level terrain that would typically be optimal for farming has large amounts of less-suitable sodium-affected Natrustalfs. Significant portions of Blaine, Phillips, and Valley Counties were glaciated approximately 150,000 years ago during the Illinoisan age. Due to erosion and dissection of the landscape, many of these areas have steeper slopes and more exposed bedrock than areas glaciated during the Wisconsin age (Fullerton and Colton, 1986).
While much of the rangeland in the aridic-ustic portion of MLRA 52 is classified as belonging to the “dry grassland” climatic zone, sites in portions of southern MLRA 52 may belong to the “dry shrubland” climatic zone. The dry shrubland zone represents the northernmost extent of the big sagebrush (Artemisia tridentata) steppe on the Great Plains. Because similar soils occur in both southern and northern portions of the MLRA, it is currently hypothesized that climate is the primary driving factor affecting big sagebrush distribution in this area. However, the precise factors are not fully understood at this time.
Sizeable tracts of largely unbroken rangeland in the eastern half of the MLRA and adjacent southern Saskatchewan are home to the Northern Montana population of greater sage-grouse (Centrocercus urophasianus), and large portions of this area are considered to be a Priority Area for Conservation (PAC) by the U.S. Fish and Wildlife Service (U.S. Fish and Wildlife Service, 2013). This population is unique among sage grouse populations because many individuals overwinter in the big sagebrush steppe (dry shrubland) in the southern portion of the MLRA and then migrate to the northern portion of the MLRA, which lacks big sagebrush (dry grassland), to live the rest of the year (Smith, 2013).
Areas of the till plain near the Bearpaw and Highwood Mountains as well as the Sweetgrass Hills and Rocky Mountain foothills are at higher elevations, receive higher amounts of precipitation, and have a typic-ustic moisture regime. These areas have significantly more rangeland production than the drier aridic-ustic portions of the MLRA and have enough moisture to produce crops annually rather than just bi-annually, as in the drier areas. Ecological sites in this higher precipitation area are classified as the moist grassland climatic zone.
Classification relationships
NRCS Soil Geography Hierarchy
• Land Resource Region: Northern Great Plains
• Major Land Resource Area (MLRA): 052 Brown Glaciated Plains
• Climate Zone: Dry Grassland
National Hierarchical Framework of Ecological Units (Cleland et al., 1997; McNab et al., 2007)
• Domain: Dry
• Division: Temperate Steppe
• Province: Great Plains-Palouse Dry Steppe Province 331
• Section: Northwestern Glaciated Plains 331D
• Subsection: Montana Glaciated Plains 331Dh
• Landtype association/Landtype phase: N/A
National Vegetation Classification Standard (Federal Geographic Data Committee, 2008)
• Class: Mesomorphic Shrub and Herb Vegetation Class (2)
• Subclass: Temperate and Boreal Grassland and Shrubland Subclass (2.B)
• Formation: Temperate Grassland, Meadow, and Shrubland Formation (2.B.2)
• Division: Great Plains Grassland and Shrubland Division (2.b.2.Nb)
• Macrogroup: Hesperostipa comata – Pascopyrum smithii – Festuca hallii Grassland Macrogroup (2.B.2.Nb.2)
• Group: Pascopyrum smithii – Hesperostipa comata – Schizachyrium scoparium Mixedgrass Prairie Group (2.B.2.Nb.2.c)
• Alliance: Pascopyrum smithii – Nassella viridula Northwestern Great Plains Herbaceous Alliance
• Association: No existing correlation
EPA Ecoregions
• Level 1: Great Plains (9)
• Level 2: West-Central Semi-Arid Prairies (9.3)
• Level 3: Northwestern Glaciated Plains (42)
• Level 4: North Central Brown Glaciated Plains (42o) & Glaciated Northern Grasslands (42j)
Ecological site concept
This provisional ecological site occurs in the Dry Grassland climatic zone of MLRA 52. Figure 1 illustrates the distribution of this ecological site based on current data. This map is approximate, is not intended to be definitive, and may be subject to change. Dense Clay Dry Grassland is a moderately extensive ecological site occurring on alluvial landscapes throughout MLRA 52. It occurs on fans, drainageways, and terraces.
The distinguishing characteristic of this site is that soils contain more than 45 percent clay in the upper 4 inches. Soils in this ecological site are typically very deep (more than 60 inches to bedrock) and derived from clayey glaciolacustrine or outwash deposits. Soil textures in the upper 4 inches are typically clay, or silty clay. The soils commonly have an ochric epipedon and weakly developed underlying horizons. Characteristic vegetation is western wheatgrass (Pascopyrum smithii), prairie Junegrass (Koeleria macrantha), and green needlegrass (Nassella viridula). The principal sagebrush species on this site is silver sagebrush (Artemisia cana), which typically only occurs at low cover.
Associated sites
FX052X01X001 |
Clayey (Cy) Dry Grassland Clayey Dry Grassland is on similar landscapes as Dense Clay Dry Grassland but is typically upslope where clay content is less. On lake plains, the Clayey site is around the perimeters whereas the Dense Clay site is closer to the center. |
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FX052X01X012 |
Dense Clay Sodic (Dcsd) Dry Grassland Dense Clay Sodic Dry Grassland is on similar landscapes as Dense Clay Dry Grassland but typically occupies the lowest position on the landscape where salts have accumulated. |
FX052X01X005 |
Clayey-Steep (Cystp) Dry Grassland Clayey Steep Dry Grassland is adjacent to Dense Clay Dry Grassland where terraces or lake plains have been dissected by streams or drainageways. The Clayey Steep site is on sideslopes whereas the Dense Clay site is on summits or toeslopes. |
Similar sites
FX052X01X012 |
Dense Clay Sodic (Dcsd) Dry Grassland This site differs from Dense Clay Dry Grassland in that soils contain accumulated salts in the upper 20 inches. This is evidenced by sodium-tolerant shrubs such as greasewood and a lack of mid-statured bunchgrasses. |
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FX052X01X001 |
Clayey (Cy) Dry Grassland This site differs from Dense Clay Dry Grassland in that clay content is greater than 35 percent but not more than 45 percent. |
FX052X99X003 |
Alkali Flat (Af) This site differs from Dense Clay Dry Grassland in that it receives additional moisture and contains accumulated salts in the upper 20 inches of soil. This site is normally on active playas that experience frequent long-duration ponding. |
FX052X03X010 |
Dense Clay (DC) Dry Shrubland This site differs from Dense Clay Dry Grassland in that it has slightly warmer annual temperatures and can support big sagebrush. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
Not specified |
Herbaceous |
Not specified |
Legacy ID
R052XY010MT
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