The Colorado River's Journey: Seven U.S. States and Two Mexican States

The Colorado River is a 2,330-km (1,450-mi) lifeline of the arid Southwest. Its basin touches seven U.S. states and two Mexican states, but the river itself flows through or forms borders of them in a specific sequence.

U.S. States (in downstream order)

1. Colorado — Headwaters in Rocky Mountain National Park (La Poudre Pass, ~3,100m). Flows west across Western Slope.
2. Utah — Enters via Westwater Canyon, carves Cataract Canyon (Canyonlands NP), fills Lake Powell (Glen Canyon Dam).
3. Arizona — Marble Canyon, Grand Canyon (277 miles in NP), Lake Mead (Hoover Dam). Forms AZ/NV border.
4. Nevada — Lake Mead shoreline only (river forms border).
5. California — River forms AZ/CA border from Lake Mead to Mexico. Imperial Dam diverts to All-American Canal (Imperial Valley) and Gila Gravity Main.
6. New Mexico — Only via tributaries (San Juan River, a major tributary, flows through NW NM). Mainstem does not enter NM.
7. Wyoming — Only via tributaries (Green River, the largest tributary by volume, rises in Wind River Range, WY). Mainstem does not enter WY.

Mexican States

1. Sonora — River forms border with Baja California after Morelos Dam. Delta begins.
2. Baja California — River forms border with Sonora, then turns south into Baja (historically) to Gulf of California (Sea of Cortez). Note: Since ~1960, the river rarely reaches the sea due to total allocation.

Key Distinction: Basin vs. Mainstem

The Colorado River Basin (637,000 km² / 246,000 mi²) includes parts of all 7 US states + 2 MX states. But the mainstem river channel only flows through/along 5 US states (CO, UT, AZ, NV, CA) and 2 MX states (Sonora, BC). NM and WY contribute massive water (Green, San Juan) but the main river doesn't enter them.

The Compact & The Crisis

The 1922 Colorado River Compact divided the basin into Upper (CO, UT, WY, NM) and Lower (AZ, NV, CA) basins, allocating 7.5 MAF/yr each + 1.5 MAF to Mexico (1944 Treaty). Total allocated (16.5 MAF) exceeds long-term average flow (~12.5 MAF, now ~11 MAF with climate change). The river is overallocated, overused, and its delta is a shadow of its former self. Renegotiation of operating guidelines (post-2026) is the defining water challenge of the Southwest.