Part of the Montana State Library collection. "July 2006"--Cover "Agreement Number : YRCDC011" Includes bibliographical references (p.16) Two reaches of the Yellowstone River riparian corridor were mapped using the U.S. Fish and Wildlife Service (USFWS) classification systems for wetlands and Western riparian types. We used two series of aerial photography (1950 and 2001) to map all of this area and also mapped the upstream reach A16 on two additional series (1976 and 1996). We evaluated but did not map a few photos from the earliest series available (1937 and 1938) for their suitability to map wetlands. Our primary objective was to evaluate the feasibility of mapping wetlands and tracking wetland change over time on historical aerial photography. Government Land Office (GLO) notes from the original land survey in early settlement times were also reviewed to determine if they could be used as a data source. All photo series were suitable for mapping wetlands although the 1950 photos for the A16 reach near Columbus had been acquired during a date of very high water levels resulting in a probable under mapping of Palustrine wetlands. The 1950 photos were also of relatively poor quality compared to all other series and some vegetation classes could not always be reliably discriminated. Any future wetland change project should make sure that the dates of imagery are comparable. The riparian corridor is extremely dynamic, as are the associated wetlands, which are created and destroyed regularly. Evaluating wetland change requires a large enough sample or total area acreage summary to be meaningful. Created ponds have increased in both reaches but especially in the more developed reach near Glendive (D6). Wetland acreage has decreased in both reaches (-7.6%) with a greater decrease in D6 (-11%). Natural wetlands have decreased even more due to the acreage of created ponds added. The less developed A16 reach was mapped on four dates of aerial photography; wetland totals varied within about a 10% range. The Riverine type varied the most, probably due to water levels and scouring from events within a few years previous to the photo date. Large peak flows are important in creating wetland sites. There may be more wetland change downstream than upstream since peak flows have diminished more downstream. The GLO notes can be used to quantify early settlement riparian vegetation and compare it to current conditions but wetlands are not distinguished. We created a crosswalk to the USFWS wetland and riparian systems from Natural Resource Conservation Service (NRCS) land use and vegetation cover classification systems used for mapping on the river. The relationship was typically complex and the NRCS minimum mapping unit is too large to identify the small wetlands often present