Which States Are in the Great Basin Region?

The **Great Basin** (hydrographic definition: internal drainage) includes **whole or parts of six states**:

Core States (Majority of Area)

• Nevada – ~85% of state; **heart of the Basin**.
• Utah – ~35% (western half: Great Salt Lake, Bonneville, Sevier basins).

Peripheral States (Significant Basins)

• Oregon – SE corner: Alvord, Catlow, Warner, Goose Lake basins (~15% of state).
• Idaho – South-central: Curlew, Raft River, Goose Creek, Bear River (upper) basins (~10%).
• California – East Sierra: Owens, Mono, Adobe, Death Valley (northern Mojave) basins (~5%).
• Wyoming – Tiny SW corner: Bear River headwaters (Great Salt Lake tributary) (<2%).

States NOT in the Great Basin

• Arizona – Colorado River drainage (except tiny Virgin River corner—disputed).
• Colorado – Green/Colorado River → Pacific.
• New Mexico – Rio Grande/Pecos → Gulf of Mexico.
• Washington – Columbia River → Pacific.

Alternative Definitions

• Physiographic (Basin & Range Province): Adds S. AZ, S. NM, W. TX, N. Mexico—**tectonic**, not hydrologic.
• Ecological (Great Basin Desert): Similar to hydrographic but excludes high mountains (Wasatch, Sierra) and Mojave transition.
• Cultural (Numic homeland): NV, UT, E CA, S OR, S ID—language family map.

**For water, law, and ecology: use the hydrographic definition (6 states). For geology: Basin & Range (wider). For culture: Numic core.**