By Michael Cohen and Emilio Mateo
September 1, 2026
This night sky image (from the NASA Earth Observatory) shows artificial lighting – a rough proxy for population – in the Colorado River Basin and adjacent areas. A close look reveals how few people actually live in the Upper Colorado River Basin. Grand Junction, Colorado, and Farmington, New Mexico, are apparent, and Rock Springs, Wyoming, is faintly visible, but the real takeaway from this image is how uninhabited the Upper Basin really is. In fact, more people live in Mexico’s portion of the Colorado River Basin than live in the Upper Basin, despite being less than 1/20th the size.
The image also shows the limited number of people and lights along the river itself. Grand Junction, Colorado; Laughlin, Nevada, and Bullhead City, Arizona; Lake Havasu City, Arizona; Yuma, Arizona; and San Luis Rio Colorado, Sonora, are the few cities and towns located along the Colorado River that appear in this image. Of these, Yuma is the largest, with slightly more than 105,000 people in 2025.
Colorado, New Mexico, Utah, and Wyoming are often described as the Upper Basin states and Arizona, California, and Nevada as the Lower Basin states. They’re officially known as the Upper Division and Lower Division states, respectively, because, as shown in the image, basin boundaries don’t follow state lines. An analysis using the Lincoln Institute map’s Colorado River Basin boundaries and US Census Block Groups reveals that, for example, more people live in Utah’s portion of the Lower Basin (mainly in St. George) than in Utah’s portion of the Upper Basin, and more people live in New Mexico’s portion of the Lower Basin than live in Wyoming’s portion of the Upper Basin.
The table below shows Census Block Group populations (in 2022) for various geographies within the Colorado River Basin; this includes about 300,000 Native Americans living on reservations within the basin. People living in the basin rely on water from Colorado River tributaries (such as the Salt River) or groundwater pumped from within the basin or on water diverted from the Colorado River itself. The Upper Basin population shown in the table is about 7% higher than the Upper Basin population Reclamation reports in its most recent Provisional Upper Colorado River System Consumptive Uses and Losses report (Table 5.4). Technical Appendix 17 (“Population and Land Use”) reports different numbers in the July 2026 Post-2026 Colorado River Reservoir Operations Final EIS. It uses county and state populations, rather than Census Block Groups, and does not account for areas within these counties that lack physical access to water from the basin.
Table 1. In-Basin Populations
| Upper Basin | 2022 Population, 1000s | |
| Arizona | 55 | |
| Colorado | 611 | |
| New Mexico | 147 | |
| Utah | 131 | |
| Wyoming | 73 | |
| 1,016 | 8% | |
| Lower Basin | ||
| Arizona | 7,266 | |
| California | 730 | |
| Nevada | 2,329 | |
| New Mexico | 75 | |
| Utah | 205 | |
| 10,605 | 82% | |
| Basin in Mexico | 1,249 | 10% |
| Total | 12,870 |
Sources: US Census Block Groups, INEGI (2020 populations in Mexico)
Adjacent Areas
This night sky image also shows heavily populated areas adjacent to – and importing water from – the Colorado River Basin, such as the Wasatch Front in Utah (including Salt Lake City and Provo), the Front Range in Colorado (including Denver, Fort Collins, and Colorado Springs), and the Metropolitan Water District of Southern California’s massive service area along the coast.
Fewer than 20 million people in Adjacent Areas use water from the basin to meet some of their needs, but in most cases they also – or mainly – use water from other sources. Combining the in-basin population that depends on basin water for all of their needs with adjacent area populations only partly reliant on basin water yields an inflated and misleading number.
The table below shows the estimated populations in these adjacent areas; please see our Municipal Deliveries report for a detailed discussion of the mixed water sources in these adjacent areas and the challenges of quantifying such populations.
Table 2. Estimated Adjacent Area Populations.
| Adjacent Areas | 2022 Populations, 1000s |
| Southern California | 12,300 |
| Front Range* | ~3,500 |
| Tijuana/Rosarito | 2,050 |
| Wasatch Front** | ~800 |
| Albuquerque/Santa Fe | 740 |
| Cheyenne, Wyoming | 70 |
| Total (rounded) | ~19,500 |
Sources: *extrapolated from Municipal Deliveries data, **calculated from
Colorado River Authority of Utah less in-basin population, and respective hyperlinks.
The Night Sky
This compelling night sky image highlights the stark differences in the numbers of people living in the Upper and Lower Basins, raising controversial questions about water allocations, reductions, equity, and privileging development aspirations over current needs.