Lithological, geophysical, paleontological and geochemical methods were used in order to define the contact relationship between the Keasey and the Cowlitz formations in northwestern Oregon. Drill cuttings from six wells located in Columbia County were analyzed by the Instrumental Neutron Activation Analysis (INAA) method. The concentrations of K, Th, Rb and Sc/Co ratio in the samples established four different groups: 1) High K, Rb, and TH, with low Sc/Co ratio typical of Cowlitz sediments. 2) Low K, Th and Rb and high Sc/Co ratio, more characteristics of the Keasey Formation. 3) Very low concentrations of Rb and high Sc, which is indicative of basaltic volcanism. 4) vertically varying K, Th and Rb concentrations. The provenance of group four is uncertain, but it may represent reworked sediments or the interfingering of the Keasey and the Cowlitz formations. Plots of these elements vs. depth define the geochemical contacts between the formations.