This paper presents the results of analyses of ground‐water conditions and water‐supplies underlying lands adjacent to San Joaquin River between Friant and Gravelly Ford Canal and their present utilization and sources of replenishment, based on an intensive field‐investigation initiated in the fall of 1936 and continued through the fall of 1938. The investigation was made under the direction of the Water Project Authority of the State of California, by the state Division of Water Resources, under the provisions of a cooperative contract with the United States Bureau of Reclamation, for the purpose of collecting data to be used in the determination of present rights to the use of San Joaquin River water inhering in lands between Friant and Gravelly Ford Canal, which would be affected by the construction and operation of the Central Valley Project. The field‐investigation included hydrographic, hydrologic, and topographic surveys and the collection and correlation of available data and information appropriate for use in a determination of the extent of present irrigation‐development and sources and amounts of available surface and underground water