Erwin Raisz’s landform map of the United States.

Raisz hand-drew landform maps of most of the Earth’s surface. The detail is amazing. We will use this to review the physiographic provinces of the United States.

Atlantic and Gulf Coastal Plains

Lowland topography underlain by (mostly) poorly lithified sedimentary rocks, dipping very gently (<0.5° mostly) toward the nearest sea. Drainage is typically dendritic, though limestone karst regions may have angular drainage. Note that the province extends up the Mississippi Embayment to southern Illinois and continues into Mexico.

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Piedmont

Rolling lowland topography underlain by deeply weathered crystalline rocks. Deep weathering and erosion usually masks underlying structure, but some very hard rocks produce pronounced ridges – Pine Mountain, GA, for example. Drainage is typically dendritic, though angular drainage is not uncommon on faulted and jointed rocks.

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Blue Ridge

Mountainous topography underlain by crystalline rocks. Lithologically similar to the Piedmont, so the cause of the extreme topographic difference is unclear. Toward the south there is a single massif, vaguely separable into eastern and western halves. North of southern VA there are two distinct high ridges and some smaller ones. Drainage is typically dendritic, though angular drainage is not uncommon, and a few areas have local trellis drainage.

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Valley and Ridge

Classic valley and ridge topography underlain by folded, well-lithified sedimentary rocks. North of southern VA this province is mort mountainous than the Blue Ridge. Drainage is typically trellis, though dendritic drainage is not uncommon in broad valleys, and a few areas have local angular drainage. Karst is found in limestone valleys.

Appalachian Plateaus (Allegheny and Cumberland)

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Upland, but not very montainous, topography underlain by well-lithified Carboniferous sedimentary rocks. North of southern VA the high Appalachians are in this province and not the Blue Ridge. Drainage is typically dendritic, though some angular drainage occurs as well. Karst is common in (Mississippian) limestone valleys.

Adirondack Mountains

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An extension of the crystalline rocks of the Canadian Shield showing less intense glacial erosion than the surrounding areas. Presumably the ice cap advances were diverted into two lobes straddling this region of high mountain peaks, like those of the southern Blue Ridge, but with features of alpine glaciation. Drainage is typically dendritic, though some angular drainage occurs as well.

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New England

Rocks as in the provinces to the south – Plateaus, Valley and Ridge, Blue Ridge/Piedmont – but with intensely glaciated lowland topography. High peaks (monadnocks) are mostly Nunataks. Drainage is typically dendritic, though some angular drainage occurs as well.

Canadian Shield (a.k.a. Laurentian Upland)

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Subdued topography on intensely (ice cap) glaciated crystalline rocks. Drainage is typically deranged, dendritic, or angular.

St Lawrence Valley

The rocks underlying this region are relatively soft shales and were more deeply gouged by the advancing ice sheets. Landforms are similar to those of the surrounding regions, but the general elevation is distinctly lower.

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Central Lowlands

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Flatland topography developed on hard, nearly horizontal Paleozoic sedimentary rocks. Weathering/erosional history varies from south to north – humid temperate weathering and fluvial erosion to the south, ice-cap glaciation to the north. Drainage is typically dendritic, though deranged drainage is common in the drift-covered areas to the north.

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Ozark Plateau

Essentially the same as the Appalachian Plateaus, but erosionally separated from that province by the Interior Lowlands and Coastal Plain (Mississippi Embayment) provinces.

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Ouachita Mountains

Essentially the same as the Valley and Ridge, but erosionally separated from that province by the Interior Lowlands and Coastal Plain (Mississippi Embayment) provinces.

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Great Plains

Flatland topography developed on soft, nearly horizontal Mesozoic and Cenozoic sedimentary rocks. Weathering/erosional history varies from south to north – humid temperate weathering and fluvial erosion to the south, ice-cap glaciation to the north. Drainage is typically dendritic, though deranged drainage occurs in the drift-covered areas to the north.

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Northern Rockies

High mountains developed on structurally deformed crystalline and hard sedimentary rocks. (Thrust) fault-line scarps predominate the structural landforms, but some folding is evident. The province is intensely glaciated by alpine glaciers.

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Southern Rockies

High mountains developed on structurally deformed crystalline and hard sedimentary rocks. (Thrust) fault-line scarps predominate the structural landforms, but some folding is evident. The province is not as intensely glaciated as the northern Rockies, but glacial features are common nevertheless.

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Wyoming Basin

A relatively low, flat area with few peaks separating the northern and southern Rockies. The region is largely underlain by young sediment derived from the adjacent mountainous areas. This has buried the original rugged topography beneath.

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Colorado Plateau

A high, flat area underlain by hard sedimentary rocks that are not structurally deformed. This is curious, since the province is completely surrounded by other provinces dominated by deformed rocks. Isostatic uplift has allowed development of deep canyons in stream systems that are typically dendritic or angular.

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Basin and Range

Typical Basin and Range topography developed on (normal or listric) fault-block structures. The “ranges” are the upthrown footwalls, the “basins” are (young) sediment fill on the downthrown hanging wall blocks. The climate is very arid, so desert landforms are common. Most of the basins are closed, so there is centripetal drainage. Some are lower than sea-level.

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Cascade and Sierra Nevada Mountains

Both of these ranges are developed on granitic batholiths exposed on the upthrown blocks of normal faults. The steeper eastern faces are the fault-line scarps. Alpine glaciers have created most of the erosional topography on these consistently hard rocks. The Cascades are the northern ranges, the Sierra Nevada the southern.

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Coast Range Mountains

The coast Ranges are tectonically uplifted areas bordering the Pacific coast. In southern California (south Marin County just north of San Francisco) the uplift is clearly and simply associated with the San Andreas Fault; farther north the pattern and causes of uplift are not as simple nor as obvious. The Olympic Mountains (northwestern Washington) have seen alpine glaciation, most of the remaining parts of the ranges have been eroded primarily by streams.

Great Valley (CA) and Willamette-Puget Lowlands (WA/OR)

These lowland areas, completely surrounded by mountains except at their river outlets, are young sedimentary fill on the down-tilted sides of the Sierra and Cascade fault blocks which has not been affected by the deformation of the Coast Ranges.