A primary goal of conservation tillage production systems has historically been to preserve residues on the soil surface as a means to reduce soil erosion losses . Residues increase surface roughness and create physical barriers that decrease erosive losses by wind and water. Early research on relationships between surface residues and soil erosion mitigation indicated that conditions in which 30% or more of the soil surface is covered by residue would result in effective soil erosion control and this threshold value for % residue became a fundamental defining characteristic of conservation tillage by the USDA Soil Conservation Service, and drove to a large extent soil conservation programs in the US for several decades. In California, where very diverse, high value cropping systems are dominant, and where soil erosion has traditionally not been as much of a management issue as in other regions, clean cultivation systems prevail and very little residue is usually found on the soil surface. With the introduction of conservation tillage (CT) systems in California in recent years, we have monitored residue cover in a variety of CT fields. In a CT tomato/corn rotation in Davis, CA, 2 – 6 times more residue was found in the CT system at planting time than under standard tillage. In a tomato/cotton study in Five Points, CA, greater than 80% cover has been determined in CT systems with cover crops. Residue management strategies and potential benefits and problems of these residues are now being investigated.