The moisture‐equivalent and specific retention have been widely used as quasi‐physical constants to measure the power of a water‐bearing material or a soil to retain water against gravitative force. Comparatively little has been demonstrated, however, as to the relation of one to the other. This paper is a preliminary statement of the apparent relation between these two measures of retentive power and is based on a study of alluvial materials made in connection with an investigation by the United States Geological Survey into the ground‐water resources of the Mokelumne Area, central California.