This series consists of over 4,500 images documenting the Irrigation Investigations Unit. The employees captured and collected these images to visually document their varied and extensive scientific research. They organized the set by their own category outline, and that intellecutual arrangement was maintained here. Each category has a three-digit number, often followed by one or two letters representing subcategories, followed by further numerical identification for each unique image. Phyically, materials are housed by format, with all prints together (Boxes 47-55), followed by glass plate negatives (Boxes 56-61), then safety film negatives (Boxes 61-62). Nitrate negatives were scanned and discarded, so exist only digitally, though some sample envelopes were saved (Box 46). Images in any given category could be in multiple formats, as specified below.

Some of the categorized subjects include dams and dam failures, flumes, snow surveys, machinery, and well drilling. There are also images taken at the Hydraulics Laboratory on the campus of the Colorado Agricultural College (now Colorado State University) and at the Bellvue laboratory on the Cache la Poudre River. Images were captured by many different individuals, including Carl Rohwer, Victor M. Cone, William E. Code, and Ralph Parshall, although most do not have an identified photographer and some were sent from other institutions. Although the majority of the photographs do not have identified locations, the geographical scope includes Colorado, Wyoming, South Dakota, North Dakota, Nebraska, Idaho, Arizona, New Mexico, and California. Beyond the categorization system, the series ends with a set of 1903 glass plate negatives of a seepage measurement trip in the Cache la Poudre River canyon and a set of about 700 snow pictures, most undated and unidentified, but some being from the Poudre Basin. A separate item-level inventory of the series can be provided on request.