Knowledge of agronomic practices across the landscape, including crops grown and conservation practices employed, is a critical requirement for success of the Conservation Effects Assessment Program (CEAP). To help achieve the goals of the Calapooia River Sub-Basin competitive grant CEAP project in western Oregon, we are developing a multi-year GIS of cropping system practices in this region dominated by grass seed production. A drive-by census of current crop production, stand establishment status, and conservation practice employment has been conducted for three consecutive growing seasons on approximately 3,000 fields in the Calapooia Sub-Basin and adjoining areas of Linn County, Oregon. Primary disturbance factors likely affecting water quality and indicator species biology are tillage, non-selective herbicide treatment, and choice of rotational crops or fallow methods between destruction of one grass seed stand and establishment of another. Although perennial grasses are grown on the majority of fields, yearly tillage of many of the fields producing Italian ryegrass seed may represent the most significant source of nitrate nitrogen in the Calapooia Sub-Basin. Classification of Landsat images into categories defined by crop species, stand age/establishment status, and conservation practice from the multi-year GIS is being used to extend our knowledge of cropping system practices across the entire Willamette River Basin. Current classification accuracy within the Calapooia Sub-Basin is approximately 75%, while accuracy is slightly lower in other randomly sampled fields in western Oregon. The greater diversity of crops produced across the entire Willamette Basin compared to the Calapooia Sub-Basin is the primary factor limiting classification accuracy in the larger area.