Orientation of the Rocky Mountains vs. Appalachian Mountains

These two great North American ranges run perpendicular to each other — shaping continental climate, ecology, and history.

Rocky Mountains

• Trend: North–South (NNW–SSE).
• Extent: ~4,800 km from Liard River (BC/YT) to Sacramento Mountains (NM).
• Structure: Multiple sub-ranges (Front, Park, Sawatch, San Juan, Sangre de Cristo, Bighorn, Wind River, Tetons, Canadian Rockies).
• Plate boundary: Laramide orogeny (flat-slab subduction) — far inland from Pacific margin.

Appalachian Mountains

• Trend: Northeast–Southwest (NE–SW).
• Extent: ~3,200 km from Newfoundland (Long Range Mts) to Alabama (Talladega).
• Structure: Long, parallel ridges (Ridge-and-Valley) + Blue Ridge + Piedmont + Plateau provinces.
• Plate boundary: Ancient collisional orogenies (Taconic, Acadian, Alleghenian) — Pangea assembly.

Why Orientation Matters

• Climate: Rockies block Pacific moisture → rain shadow (Great Plains, Intermontane basins). Appalachians intercept Gulf/Atlantic moisture → orographic rain on windward slopes.
• Migration corridors: N–S Rockies = north-south wildlife highways. NE–SW Appalachians = diagonal corridors; east-west barriers.
• Human history: Rockies = barrier to westering (South Pass key). Appalachians = barrier to interior (Cumberland Gap key).

Together, they form the backbone and ribs of the continent.