This series consists of photographs and maps of the Blue River Basin in Colorado, along with associated textual documents. The headwaters of Colorado's Blue River primarily originate from the Tenmile (or Ten Mile) and Gore ranges in the Rocky Mountains. From below the Fremont, Hoosier, Loveland, and Vail passes, the Blue River runs 65 miles north with inflows from 63 sub-basins to its confluence with the Colorado River near the town of Kremmling. The basin is divided into the Upper Basin, which covers the headwaters to Dillon Reservoir, and the Lower Basin, which continues down through Green Mountain Reservoir to the Colorado River. The system is largely fed by snowmelt. The big snow years of 1995-1997 produced a high amount of runoff, documented by photographs in this collection. Agriculture (ranches), domestic, municipal, and storage are the primary uses for Blue River water, along with hydroelectric power. Transmountain diversion projects, for both Denver and Colorado Springs, direct a substantial part of the river's flow into the South Platte River and Arkansas River for use along the Front Range.

The 500+ photographs here show the river and tributaries, reservoirs and tarns, headgates, flumes, spillways, dams, high-water events, snow, and surrounding mountains. Some photographs have accompanying negatives. Geographic locations within Colorado Water District 36 include the Blue River and sub-basins, Dillon Reservoir, Green Mountain Reservoir, and the counties of Grand, Summit, and Lake. Photographs were arranged geographically from the Blue River's headwaters to its outlet at the Colorado River. Folders were created based on tributaries, reservoirs, and townships. Photographs with no identified location are at the end.

The oversize materials are primarily U.S. Geological Survey and U.S. Forest Service maps along with some early township maps by the Surveyor General's Office. The maps focus on District 36 and neighboring areas but also include other places on Colorado's West Slope. Many of the maps are annotated. Also included is a set of data sheets listing diversions in Water District 36 and a straight line diagram notebook. These materials are followed by files of Hummer's letters and thank-you notes, reference materials, and publications.