Natural Resources
Conservation Service
Ecological site FX053A99X022
Loamy Gravel (LoGr)
Last updated: 11/22/2023
Accessed: 11/13/2024
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): 053A–Northern Dark Brown Glaciated Plains
The Northern Dark Brown Glaciated Plains, MLRA 53A, is a large, agriculturally and ecologically significant area. It consists of approximately 6.1 million acres and stretches 140 miles from east to west and 120 miles from north to south, encompassing portions of 8 counties in northeastern Montana and northwestern North Dakota. This region represents part of the southern edge of the Laurentide Ice Sheet during maximum glaciation. It is one of the driest and westernmost areas within the vast network of glacially derived prairie pothole landforms of the Northern Great Plains and falls roughly between the Missouri Coteau to the east and the Brown Glaciated Plains to the west. Elevation ranges from 1,800 feet (550 meters) to 3,300 feet (1,005 meters).
Soils are primarily Mollisols, but Inceptisols and Entisols 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 (Soller, 2001). Underlying the till is sedimentary bedrock largely consisting of Cretaceous shale, sandstone, and mudstone (Vuke et al., 2007). The bedrock is commonly exposed on hillslopes, particularly along drainageways. Significant alluvial deposits occur in glacial outwash channels and along major drainages, including portions of the Missouri, Poplar, and Big Muddy Rivers. Large eolian deposits of sand occur in the vicinity of the ancestral Missouri River channel east of Medicine Lake (Fullerton et al., 2004). The northwestern portion of the MLRA contains a large unglaciated area containing paleoterraces and large deposits of sand and gravel known as the Flaxville gravel.
Much of this MLRA was glaciated towards the end of the Wisconsin age, and the maximum glacial extent occurred approximately 20,000 years ago (Fullerton and Colton, 1986; Fullerton et al., 2004). Subsequent erosion from major stream and river systems has created numerous drainageways throughout much of the MLRA. The result is a geologically young landscape that is predominantly a dissected till plain interspersed with alluvial deposits and dominated by soils in the Mollisol and Inceptisol orders. Much of this area is typic ustic, making these soils very productive and generally well suited to production agriculture.
Dryland farming is the predominant land use, and approximately 50 percent of the land area is used for cultivated crops. Winter, spring, and durum varieties of wheat are the major crops, with over 48 million bushels produced annually (USDA-NASS, 2017). Areas of rangeland typically are on steep hillslopes along drainages. The rangeland is mostly native mixed-grass prairie similar to the Stipa-Agropyron, Stipa-Bouteloua-Agropyron, and Stipa-Bouteloua faciations (Coupland, 1950, 1961). Cool-season grasses dominate and include rhizomatous wheatgrasses, needle and thread, western porcupine grass, and green needlegrass. Woody species are generally rare; however, many of the steeper drainages support stands of trees and shrubs, such as green ash and chokecherry. Seasonally ponded, prairie pothole wetlands may occur throughout the MLRA, but the greatest concentrations are in the east and northeast where receding glaciers stagnated and formed disintegration moraines with hummocky topography and numerous areas of poorly drained soils.
Classification relationships
NRCS Soil Geography Hierarchy
• Land Resource Region: Northern Great Plains
• Major Land Resource Area (MLRA): 053A Northern Dark Brown Glaciated Plains
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: Glaciated Northern Grasslands Section 331L
• Subsection: Glaciated Northern Grasslands Subsection 331La
• 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 and Shrubland Formation (2.B.2)
• Division: Central North American and Shrubland Division (2.B.2.Nb)
• Macrogroup: Hesperostipa comata - Pascopyrum smithii - Festuca hallii Grassland Macrogroup (2.B.2.Nb.2)
o Group: Hesperostipa comata - Bouteloua gracilis Dry Mixedgrass Prairie Group (2.B.2.Nb.2.b)
EPA Ecoregions
• Level 1: Great Plains (9)
• Level 2: West-Central Semi-Arid Prairies (9.3)
• Level 3: Northwestern Glaciated Plains (42)
• Level 4: Glaciated Dark Brown Prairie (42i)
Glaciated Northern Grasslands (42j)
Ecological site concept
Loamy Gravel is a common ecological site occurring on outwash fans, terraces, and kames that have been overtopped with glacial till. The distinguishing characteristic of this site is that the upper 20 inches of soil is predominantly loamy skeletal, meaning that it contains 35 percent or more coarse fragments, has a texture class finer than loamy fine sand, and contains less than 35 percent clay (Soil Survey Staff, 2014). Soils for this ecological site are typically deep to very deep (more than 40 inches), excessively drained, and derived from gravelly alluvium or glacial outwash. Characteristic vegetation is cool-season rhizomatous grasses and mid-statured, cool-season bunchgrasses.
Associated sites
FX053A99X032 |
Loamy (Lo) The Loamy Dry ecological site is on similar landscapes and slope positions as the Loamy Gravel ecological site. It is adjacent to the Loamy Gravel ecological site but only occurs where slopes are less than 15 percent and coarse fragment content is less than 35 percent. |
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FX053A99X021 |
Sandy Gravel (SyGr) The Sandy Gravel ecological site is on similar landscapes and slope positions as the Loamy Gravel ecological site. It is adjacent to the Loamy Gravel ecological site, but only occurs where fine-earth textures are loamy fine sand or coarser. |
FX053A99X062 |
Swale (Se) The Swale ecological site is downslope from the Loamy Gravel ecological site. It is on similar landscapes but in swales that receive additional moisture. |
Similar sites
FX053A99X032 |
Loamy (Lo) This site differs from Loamy Gravel ecological site in that it contains less than 35 percent coarse fragments in the upper 20 inches of soil. |
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FX053A99X021 |
Sandy Gravel (SyGr) This site differs from Loamy Gravel ecological site in that its soils are sandy skeletal rather than loamy skeletal, meaning that fine-earth textures are loamy fine sand or coarser. Percent clay in the fine-earth fraction is typically less than 18 percent. |
Table 1. Dominant plant species
Tree |
Not specified |
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Shrub |
Not specified |
Herbaceous |
(1) Pascopyrum smithii |
Legacy ID
R053AY707MT
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Ecosystem states
States 2 and 5 (additional transitions)
T1A | - | Introduction of non-native grass species, such as crested wheatgrass and Kentucky bluegrass. |
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T2A | - | Prolonged drought, improper grazing management, or a combination of these factors |
T2B | - | Displacement of native species by non-native invasive species (Crested Wheatgrass, Kentucky bluegrass, noxious weeds, etc.) |
T2C | - | Conversion to cropland |
R3A | - | Range seeding, grazing land mechanical treatment, timely moisture, proper grazing management (management intensive and costly) |
T3B | - | Conversion to cropland |
T4A | - | Conversion to cropland |
T5A | - | Cessation of annual cropping |
T6A | - | Conversion to cropland |
State 1 submodel, plant communities
State 2 submodel, plant communities
P2.1a | - | Drought, improper grazing management |
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P2.2a | - | Return to normal or above average precipitation, proper grazing management |