Design studies for Oroville Dam, a 735-ft high embankment dam now under construction, called for extensive material exploration because of the large quantities of materials required. The dam, which will contain 77 million cu yd of material, is located on the Feather River, 5 miles northeast of Oroville, Butte County, Calif. Original concrete-aggregate exploration and subsequent impervious and pervious materials exploration required procedures and techniques that would provide representative samples of material for testing and a reliable analysis of the in situ characteristics of the areas. A 7000-acre tailings deposit, which was the result of gold dredging along the Feather River downstream from Oroville, was investigated as a source for concrete aggregate and later for transition and pervious embankment material. A unique hole excavator and several types of casing were used in the very loose tailing deposit during the concrete aggregate investigation, and an elaborate field grading procedure was followed. Later exploration was accomplished by dragline, bulldozer, and backhoe. Impervious core material explorations were confined to clayey gravels adjacent to the tailing deposit. Bucket augers were used to drill 30-in. diameter uncased holes for most of the impervious borrow exploration. Field grading equipment was improved and mechanized and over 100 holes were drilled; excavated materials were logged, field graded, and sampled. Through careful analysis and control of the exploration procedures and techniques, it was concluded that samples used for laboratory testing and from which design values were obtained are adequately representative of the in situ deposits. For any extensive materials' exploration requiring field grading, mechanization of equipment is recommended.