Water is the West's essential resource, and managing it well depends on accurate, timely information. Documenting the Colorado River Basin's water began with John Wesley Powell's exploration of the Colorado and its tributaries in the summer of 1869. The U.S. Geological Survey was created in 1879, and its first systematic streamflow measurements began in 1889 at its first streamgage, 08279500 Rio Grande at Embudo, New Mexico.
*Figure 3.U.S. Geological Survey staff making a streamflow measurement using an acoustic Doppler
current profiler at U.S. Geological Survey 09076000 Maroon Creek near Aspen, Colorado
streamgage. Photograph by U.S. Geological Survey.*
Across its 146 years, USGS has gathered water data at strategic places in the West to support water management, flood forecasting and response, transfers between basins, hydropower, city and farm supplies, food security, recreation, habitat, treaty and river-compact obligations, and major reservoirs such as Lake Powell, on the Utah–Arizona border, and Lake Mead, on the Nevada–Arizona border.
The USGS 09188500 Green River at Warren Bridge streamgage near Daniel, Wyoming, in 1961. USGS photo.
*Figure 2.High flow at U.S. Geological Survey 09379500 San Juan River near Bluff, Utah streamgage.
Photograph by U.S. Geological Survey.*
The hardest-working river
The Colorado River has been called the hardest-working river in the West. Its 240,000-square-mile drainage supplies water to about 40 million people, 29 Tribes, 7 States and 2 countries, and irrigates about 4.5 million acres. The basin takes in parts of Arizona, California, Colorado, Nevada, New Mexico, Utah and Wyoming, and extends into Mexico.
The Upper Colorado River Basin is everything upstream of streamgage 09380000, Colorado River at Lees Ferry, Arizona, including the Paria River basin. At approximately 130,000 square miles, it produces about 92 percent of the whole basin's streamflow. A yearly supply shortfall and a drought of more than 20 years have strained reservoir storage and water security, so managers need comprehensive, accurate, impartial data in real time.
The Upper Colorado River Basin, with 352 USGS streamgages (33 of them "Centennial"), 71 precipitation gages and 10 offices that maintain the network. USGS.
The network
- The oldest gages, 09315000 Green River at Green River, Utah, and 09152500 Gunnison River near Grand Junction, Colorado, began work in 1894 and have recorded for 130 years.
- 352 streamgages operated in the Upper Basin as of July 30, 2025; 33 are "Centennial" gages with more than 100 years of records. The network has grown substantially in recent years and may keep growing.
- 71 precipitation gages, many at streamgages, were running as of March 2025. Precipitation data are central to flood warning and to modeling the water balance of mountain terrain.
- Beyond streamflow, USGS is adding snowpack, soil moisture, water quality, groundwater and atmospheric sensors, which help with emerging problems such as variable snowpack, wildfire effects and salinity. The fine-scale data feed the USGS National Water Monitoring Network and are available through its databases and online tools.
(A) Downloading data at the Andrews Creek meteorological station in Rocky Mountain National Park, Colorado. (B) A precipitation gage in a wildfire burn scar, used for flood warning. USGS photos.
New tools
Gages now also measure precipitation, surface velocity, water temperature, specific conductance, dissolved oxygen, turbidity, pH and nitrate. Field crews carry noncontact velocity sensors, real-time cameras, under-ice sensors, submersible velocity meters, lidar and uncrewed aircraft. Together with better software, these give more accurate measurements, better data in floods, droughts and ice, and more efficient field work, with extra data streams used to decide where crews go first.
Calibrating the streamgage, surface velocity radar and camera at 09132095 Anthracite Creek above mouth near Somerset, Colorado, with an acoustic Doppler current profiler during snowmelt. USGS photo.
(A) Programming sensors on an uncrewed aircraft system. (B) Servicing water-quality sensors at 09359020 Animas River below Silverton, Colorado. USGS photos.
Who pays for it
The network runs on a mix of congressionally appropriated USGS funds and money from more than 75 Federal, Tribal, State and local partners. Pooling the two widens what is measured and gives water managers the data they need to protect life, property, the environment and the economy.
Measuring from a cableway with an acoustic Doppler current profiler at 09211200 Green River below Fontenelle Reservoir, Wyoming. USGS photo.
Sources
Rewritten from the U.S. Geological Survey Fact Sheet 2025–3039, "U.S. Geological Survey streamgage network in the Upper Colorado River Basin—Recording the hydrologic history of the West" (public domain), in hubnx's own words. The fact sheet calls the Upper Basin's approximately 130,000 square miles "less than half" of a 240,000-square-mile basin; that comparison is left out. Pictures an earlier version of this page left out were restored on 2026-09-26.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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