The Only U.S. Mountain Range Running East–West: The Adirondacks (New York)

The Adirondack Mountains in northern New York State are the only major mountain range in the contiguous United States with a predominant east–west orientation.

Why It's Unique

• Most NA ranges run north–south (Rockies, Appalachians, Sierra Nevada, Cascades, Wasatch, etc.) — aligned with tectonic plate boundaries.
• The Adirondacks are a dome — a circular uplift (Adirondack Dome) of ancient Precambrian rock (>1 billion years), not a linear fold belt. Erosion carved radial drainage, but the structural grain and high peaks (High Peaks region) trend northeast–southwest to east–west.
• 46 High Peaks >4,000 ft (including Mt. Marcy, 5,344 ft — NY's highest) form a rough east–west cluster.

Geological Context

Part of the Grenville Province (Canadian Shield extension). Uplifted ~10–20 Mya (recent geologically) by a mantle hotspot/plume — distinct from Appalachian orogeny. Still rising ~1.5 mm/yr.

Not the Only "East-West" Hills

• Uinta Mountains (UT) — also east–west, but Rockies sub-range, not a separate range.
• Transverse Ranges (CA) — east–west, but fault-block, coastal.
• Brooks Range (AK) — east–west, but Arctic.

The Adirondacks stand alone as a major, discrete, dome-derived east–west range in the Lower 48 — a geological anomaly and a hiker's paradise (ADK 46ers).